Basic Programming Guide
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Reference Manual
Volume I
Basic Programming Guide
Version 6.30
March 17th 2015
CLIPS Reference Manual
CLIPS Basic Programming Guide
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CLIPS Basic Programming Guide
Version 6.30 March 17th 2015
CONTENTS
License Information ....................................................................................................................... i!
Preface ........................................................................................................................................... iii!
Acknowledgements ...................................................................................................................... vii!
Section 1: Introduction .................................................................................................................. 1!
Section 2: CLIPS Overview .......................................................................................................... 3!
2.1 Interacting with CLIPS ........................................................................................................ 3!
2.1.1 Top Level Commands ................................................................................................ 3!
2.1.2 Automated Command Entry and Loading .................................................................. 4!
2.1.3 Integration with Other Programming Languages ....................................................... 5!
2.2 Reference Manual Syntax .................................................................................................... 5!
2.3 Basic Programming Elements ............................................................................................. 6!
2.3.1 Data Types .................................................................................................................. 6!
2.3.2 Functions .................................................................................................................... 9!
2.3.3 Constructs ................................................................................................................. 10!
2.4 Data Abstraction ................................................................................................................ 11!
2.4.1 Facts .......................................................................................................................... 11!
2.4.2 Objects ...................................................................................................................... 13!
2.4.3 Global Variables ....................................................................................................... 15!
2.5 Knowledge Representation ................................................................................................ 15!
2.5.1 Heuristic Knowledge – Rules ................................................................................... 15!
2.5.2 Procedural Knowledge ............................................................................................. 16!
2.6 CLIPS Object-Oriented Language .................................................................................... 18!
2.6.1 COOL Deviations from a Pure OOP Paradigm ........................................................ 18!
2.6.2 Primary OOP Features .............................................................................................. 18!
2.6.3 Instance-set Queries and Distributed Actions .......................................................... 19!
Section 3: Deftemplate Construct ............................................................................................. 21!
3.1 Slot Default Values ............................................................................................................ 22!
3.2 Slot Default Constraints for Pattern-Matching .................................................................. 23!
3.3 Slot Value Constraint Attributes ....................................................................................... 23!
3.4 Implied Deftemplates ........................................................................................................ 23!
Section 4: Deffacts Construct .................................................................................................... 25!
Section 5: Defrule Construct ..................................................................................................... 27!
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5.1 Defining Rules ................................................................................................................... 27!
5.2 Basic Cycle Of Rule Execution ......................................................................................... 28!
5.3 Conflict Resolution Strategies ........................................................................................... 29!
5.3.1 Depth Strategy .......................................................................................................... 29!
5.3.2 Breadth Strategy ....................................................................................................... 29!
5.3.3 Simplicity Strategy ................................................................................................... 29!
5.3.4 Complexity Strategy ................................................................................................. 30!
5.3.5 LEX Strategy ............................................................................................................ 30!
5.3.6 MEA Strategy ........................................................................................................... 31!
5.3.7 Random Strategy ...................................................................................................... 32!
5.4 LHS Syntax ....................................................................................................................... 33!
5.4.1 Pattern Conditional Element ..................................................................................... 34!
5.4.2 Test Conditional Element ......................................................................................... 51!
5.4.3 Or Conditional Element ............................................................................................ 52!
5.4.4 And Conditional Element ......................................................................................... 53!
5.4.5 Not Conditional Element .......................................................................................... 54!
5.4.6 Exists Conditional Element ...................................................................................... 55!
5.4.7 Forall Conditional Element ...................................................................................... 56!
5.4.8 Logical Conditional Element .................................................................................... 58!
5.4.9 Automatic Replacement of LHS CEs ....................................................................... 61!
5.4.10 Declaring Rule Properties ....................................................................................... 62!
Section 6: Defglobal Construct .................................................................................................. 65!
Section 7: Deffunction Construct .............................................................................................. 71!
Section 8: Generic Functions ..................................................................................................... 75!
8.1 Note on the Use of the Term Method ................................................................................ 75!
8.2 Performance Penalty of Generic Functions ....................................................................... 76!
8.3 Order Dependence of Generic Function Definitions ......................................................... 76!
8.4 Defining a New Generic Function ..................................................................................... 76!
8.4.1 Generic Function Headers ........................................................................................ 77!
8.4.2 Method Indices ......................................................................................................... 77!
8.4.3 Method Parameter Restrictions ................................................................................ 78!
8.4.4 Method Wildcard Parameter ..................................................................................... 79!
8.5 Generic Dispatch ............................................................................................................... 81!
8.5.1 Applicability of Methods Summary ......................................................................... 82!
8.5.2 Method Precedence .................................................................................................. 84!
8.5.3 Shadowed Methods .................................................................................................. 86!
8.5.4 Method Execution Errors ......................................................................................... 86!
8.5.5 Generic Function Return Value ................................................................................ 87!
Section 9: CLIPS Object Oriented Language .......................................................................... 89!
9.1 Background ........................................................................................................................ 89!
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9.2 Predefined System Classes ................................................................................................ 89!
9.3 Defclass Construct ............................................................................................................. 91!
9.3.1 Multiple Inheritance ................................................................................................. 92!
9.3.2 Class Specifiers ........................................................................................................ 95!
9.3.3 Slots .......................................................................................................................... 95!
9.3.4 Message-handler Documentation ........................................................................... 105!
9.4 Defmessage-handler Construct ........................................................................................ 106!
9.4.1 Message-handler Parameters .................................................................................. 108!
9.4.2 Message-handler Actions ....................................................................................... 109!
9.4.3 Daemons ................................................................................................................. 111!
9.4.4 Predefined System Message-handlers .................................................................... 112!
9.5 Message Dispatch ............................................................................................................ 116!
9.5.1 Applicability of Message-handlers ......................................................................... 118!
9.5.2 Message-handler Precedence .................................................................................. 118!
9.5.3 Shadowed Message-handlers .................................................................................. 118!
9.5.4 Message Execution Errors ...................................................................................... 119!
9.5.5 Message Return Value ............................................................................................ 120!
9.6 Manipulating Instances .................................................................................................... 120!
9.6.1 Creating Instances .................................................................................................. 120!
9.6.2 Reinitializing Existing Instances ............................................................................ 124!
9.6.3 Reading Slots .......................................................................................................... 125!
9.6.4 Setting Slots ............................................................................................................ 125!
9.6.5 Deleting Instances .................................................................................................. 126!
9.6.6 Delayed Pattern-Matching When Manipulating Instances ..................................... 126!
9.6.7 Modifying Instances ............................................................................................... 127!
9.6.8 Duplicating Instances ............................................................................................. 129!
9.7 Instance-set Queries and Distributed Actions ................................................................. 132!
9.7.1 Instance-set Definition ............................................................................................ 135!
9.7.2 Instance-set Determination ..................................................................................... 135!
9.7.3 Query Definition ..................................................................................................... 137!
9.7.4 Distributed Action Definition ................................................................................. 137!
9.7.5 Scope in Instance-set Query Functions .................................................................. 138!
9.7.6 Errors during Instance-set Query Functions ........................................................... 139!
9.7.7 Halting and Returning Values from Query Functions ............................................ 139!
9.7.8 Instance-set Query Functions ................................................................................. 139!
Section 10: Defmodule Construct ............................................................................................ 145!
10.1 Defining Modules .......................................................................................................... 145!
10.2 Specifying a Construct’s Module .................................................................................. 146!
10.3 Specifying Modules ....................................................................................................... 147!
10.4 Importing and Exporting Constructs ............................................................................. 147!
10.4.1 Exporting Constructs ............................................................................................ 148!
10.4.2 Importing Constructs ............................................................................................ 149!
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10.5 Importing and Exporting Facts and Instances ............................................................... 150!
10.5.1 Specifying Instance-Names .................................................................................. 150!
10.6 Modules and Rule Execution ......................................................................................... 151!
Section 11: Constraint Attributes ........................................................................................... 153!
11.1 Type Attribute ............................................................................................................... 153!
11.2 Allowed Constant Attributes ......................................................................................... 154!
11.3 Range Attribute ............................................................................................................. 155!
11.4 Cardinality Attribute ...................................................................................................... 155!
11.5 Deriving a Default Value From Constraints .................................................................. 156!
11.6 Constraint Violation Examples ...................................................................................... 157!
Section 12: Actions And Functions ......................................................................................... 159!
12.1 Predicate Functions ....................................................................................................... 159!
12.1.1 Testing For Numbers ............................................................................................ 159!
12.1.2 Testing For Floats ................................................................................................. 159!
12.1.3 Testing For Integers .............................................................................................. 159!
12.1.4 Testing For Strings Or Symbols ........................................................................... 160!
12.1.5 Testing For Strings ............................................................................................... 160!
12.1.6 Testing For Symbols ............................................................................................. 160!
12.1.7 Testing For Even Numbers ................................................................................... 160!
12.1.8 Testing For Odd Numbers .................................................................................... 161!
12.1.9 Testing For Multifield Values .............................................................................. 161!
12.1.10 Testing For External-Addresses ......................................................................... 161!
12.1.11 Comparing for Equality ...................................................................................... 161!
12.1.12 Comparing for Inequality ................................................................................... 162!
12.1.13 Comparing Numbers for Equality ...................................................................... 162!
12.1.14 Comparing Numbers for Inequality .................................................................... 163!
12.1.15 Greater Than Comparison .................................................................................. 163!
12.1.16 Greater Than or Equal Comparison .................................................................... 164!
12.1.17 Less Than Comparison ....................................................................................... 164!
12.1.18 Less Than or Equal Comparison ........................................................................ 165!
12.1.19 Boolean And ....................................................................................................... 165!
12.1.20 Boolean Or .......................................................................................................... 165!
12.1.21 Boolean Not ........................................................................................................ 166!
12.2 Multifield Functions ...................................................................................................... 166!
12.2.1 Creating Multifield Values ................................................................................... 166!
12.2.2 Specifying an Element .......................................................................................... 166!
12.2.3 Finding an Element ............................................................................................... 167!
12.2.4 Comparing Multifield Values ............................................................................... 167!
12.2.5 Deletion of Fields in Multifield Values ................................................................ 168!
12.2.6 Creating Multifield Values from Strings. ............................................................. 168!
12.2.7 Creating Strings from Multifield Values .............................................................. 169!
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12.2.8 Extracting a Sub-sequence from a Multifield Value ............................................ 169!
12.2.9 Replacing Fields within a Multifield Value ......................................................... 170!
12.2.10 Inserting Fields within a Multifield Value ......................................................... 170!
12.2.11 Getting the First Field from a Multifield Value ................................................. 171!
12.2.12 Getting All but the First Field from a Multifield Value ..................................... 171!
12.2.13 Determining the Number of Fields in a Multifield Value .................................. 172!
12.2.14 Deleting Specific Values within a Multifield Value .......................................... 172!
12.2.15 Replacing Specific Values within a Multifield Value ........................................ 172!
12.3 String Functions ............................................................................................................. 173!
12.3.1 String Concatenation ............................................................................................ 173!
12.3.2 Symbol Concatenation .......................................................................................... 173!
12.3.3 Taking a String Apart ........................................................................................... 174!
12.3.4 Searching a String ................................................................................................. 174!
12.3.5 Evaluating a Function within a String .................................................................. 175!
12.3.6 Evaluating a Construct within a String ................................................................. 175!
12.3.7 Converting a String to Uppercase ......................................................................... 176!
12.3.8 Converting a String to Lowercase ........................................................................ 176!
12.3.9 Comparing Two Strings ....................................................................................... 176!
12.3.10 Determining the Length of a String .................................................................... 177!
12.3.11 Checking the Syntax of a Construct or Function Call within a String ............... 177!
12.3.12 Converting a String to a Field ............................................................................ 178!
12.4 The CLIPS I/O System .................................................................................................. 178!
12.4.1 Logical Names ...................................................................................................... 179!
12.4.2 Common I/O Functions ........................................................................................ 179!
12.5 Math Functions .............................................................................................................. 189!
12.5.1 Standard Math Functions ...................................................................................... 189!
12.5.2 Extended Math Functions ..................................................................................... 194!
12.6 Procedural Functions ..................................................................................................... 199!
12.6.1 Binding Variables ................................................................................................. 199!
12.6.2 If...then...else Function ......................................................................................... 200!
12.6.3 While .................................................................................................................... 201!
12.6.4 Loop-for-count ..................................................................................................... 202!
12.6.5 Progn ..................................................................................................................... 203!
12.6.6 Progn$ ................................................................................................................... 203!
12.6.7 Return ................................................................................................................... 204!
12.6.8 Break ..................................................................................................................... 204!
12.6.9 Switch ................................................................................................................... 205!
12.6.10 Foreach ............................................................................................................... 206!
12.7 Miscellaneous Functions ............................................................................................... 207!
12.7.1 Gensym ................................................................................................................. 207!
12.7.2 Gensym* ............................................................................................................... 207!
12.7.3 Setgen ................................................................................................................... 208!
12.7.4 Random ................................................................................................................. 208!
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12.7.5 Seed ...................................................................................................................... 209!
12.7.6 Time ...................................................................................................................... 209!
12.7.7 Number of Fields or Characters in a Data Object ................................................ 209!
12.7.8 Determining the Restrictions for a Function ........................................................ 210!
12.7.9 Sorting a List of Values ........................................................................................ 210!
12.7.10 Calling a Function .............................................................................................. 211!
12.7.11 Timing Functions and Commands ...................................................................... 211!
12.7.12 Determining the Operating System .................................................................... 211!
12.8 Deftemplate Functions ................................................................................................... 212!
12.8.1 Determining the Module in which a Deftemplate is Defined ............................... 212!
12.8.2 Getting the Allowed Values for a Deftemplate Slot ............................................. 212!
12.8.3 Getting the Cardinality for a Deftemplate Slot ..................................................... 212!
12.8.4 Testing whether a Deftemplate Slot has a Default ............................................... 213!
12.8.5 Getting the Default Value for a Deftemplate Slot ................................................ 214!
12.8.6 Deftemplate Slot Existence .................................................................................. 214!
12.8.7 Testing whether a Deftemplate Slot is a Multifield Slot ...................................... 215!
12.8.8 Determining the Slot Names Associated with a Deftemplate .............................. 215!
12.8.9 Getting the Numeric Range for a Deftemplate Slot ............................................. 215!
12.8.10 Testing whether a Deftemplate Slot is a Single-Field Slot ................................. 216!
12.8.11 Getting the Primitive Types for a Deftemplate Slot ........................................... 216!
12.8.12 Getting the List of Deftemplates ........................................................................ 217!
12.9 Fact Functions ............................................................................................................... 217!
12.9.1 Creating New Facts .............................................................................................. 217!
12.9.2 Removing Facts from the Fact-list ....................................................................... 218!
12.9.3 Modifying Template Facts ................................................................................... 219!
12.9.4 Duplicating Template Facts .................................................................................. 220!
12.9.5 Asserting a String ................................................................................................. 220!
12.9.6 Getting the Fact-Index of a Fact-address .............................................................. 221!
12.9.7 Determining If a Fact Exists ................................................................................. 222!
12.9.8 Determining the Deftemplate (Relation) Name Associated with a Fact .............. 222!
12.9.9 Determining the Slot Names Associated with a Fact ........................................... 222!
12.9.10 Retrieving the Slot Value of a Fact .................................................................... 223!
12.9.11 Retrieving the Fact-List ...................................................................................... 224!
12.9.12 Fact-set Queries and Distributed Actions ........................................................... 224!
12.10 Deffacts Functions ....................................................................................................... 234!
12.10.1 Getting the List of Deffacts ................................................................................ 234!
12.10.2 Determining the Module in which a Deffacts is Defined ................................... 234!
12.11 Defrule Functions ........................................................................................................ 235!
12.11.1 Getting the List of Defrules ................................................................................ 235!
12.11.2 Determining the Module in which a Defrule is Defined .................................... 235!
12.12 Agenda Functions ........................................................................................................ 235!
12.12.1 Getting the Current Focus .................................................................................. 235!
12.12.2 Getting the Focus Stack ...................................................................................... 236!
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12.12.3 Removing the Current Focus from the Focus Stack ........................................... 236!
12.13 Defglobal Functions .................................................................................................... 237!
12.13.1 Getting the List of Defglobals ............................................................................ 237!
12.13.2 Determining the Module in which a Defglobal is Defined ................................ 238!
12.14 Deffunction Functions ................................................................................................. 238!
12.14.1 Getting the List of Deffunctions ......................................................................... 238!
12.14.2 Determining the Module in which a Deffunction is Defined ............................. 238!
12.15 Generic Function Functions ........................................................................................ 238!
12.15.1 Getting the List of Defgenerics .......................................................................... 239!
12.15.2 Determining the Module in which a Generic Function is Defined .................... 239!
12.15.3 Getting the List of Defmethods .......................................................................... 239!
12.15.4 Type Determination ............................................................................................ 240!
12.15.5 Existence of Shadowed Methods ........................................................................ 240!
12.15.6 Calling Shadowed Methods ................................................................................ 240!
12.15.7 Calling Shadowed Methods with Overrides ....................................................... 241!
12.15.8 Calling a Specific Method .................................................................................. 242!
12.15.9 Getting the Restrictions of Defmethods ............................................................. 243!
12.16 CLIPS Object-Oriented Language (COOL) Functions ............................................... 244!
12.16.1 Class Functions ................................................................................................... 244!
12.16.2 Message-handler Functions ................................................................................ 254!
12.16.3 Definstances Functions ....................................................................................... 256!
12.16.4 Instance Manipulation Functions and Actions ................................................... 256!
12.17 Defmodule Functions .................................................................................................. 263!
12.17.1 Getting the List of Defmodules .......................................................................... 263!
12.17.2 Setting the Current Module ................................................................................ 263!
12.17.3 Getting the Current Module ................................................................................ 263!
12.18 Sequence Expansion .................................................................................................... 264!
12.18.1 Sequence Expansion and Rules .......................................................................... 265!
12.18.2 Multifield Expansion Function ........................................................................... 266!
12.18.3 Setting The Sequence Operator Recognition Behavior ...................................... 266!
12.18.4 Getting The Sequence Operator Recognition Behavior ..................................... 267!
12.18.5 Sequence Operator Caveat ................................................................................. 267!
Section 13: Commands ............................................................................................................. 269!
13.1 Environment Commands ............................................................................................... 269!
13.1.1 Loading Constructs From A File .......................................................................... 269!
13.1.2 Loading Constructs From A File without Progress Information .......................... 269!
13.1.3 Saving All Constructs To A File .......................................................................... 270!
13.1.4 Loading a Binary Image ....................................................................................... 270!
13.1.5 Saving a Binary Image ......................................................................................... 270!
13.1.6 Clearing CLIPS .................................................................................................... 271!
13.1.7 Exiting CLIPS ...................................................................................................... 271!
13.1.8 Resetting CLIPS ................................................................................................... 271!
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13.1.9 Executing Commands From a File ....................................................................... 272!
13.1.10 Executing Commands From a File Without Replacing Standard Input ............. 272!
13.1.11 Determining CLIPS Compilation Options ......................................................... 273!
13.1.12 Calling the Operating System ............................................................................. 273!
13.1.13 Setting The Auto-Float Dividend Behavior ....................................................... 273!
13.1.14 Getting The Auto-Float Dividend Behavior ....................................................... 274!
13.1.15 Setting the Dynamic Constraint Checking Behavior .......................................... 274!
13.1.16 Getting the Dynamic Constraint Checking Behavior ......................................... 274!
13.1.17 Setting the Static Constraint Checking Behavior ............................................... 274!
13.1.18 Getting the Static Constraint Checking Behavior .............................................. 275!
13.1.19 Finding Symbols ................................................................................................. 275!
13.2 Debugging Commands .................................................................................................. 275!
13.2.1 Generating Trace Files ......................................................................................... 275!
13.2.2 Closing Trace Files ............................................................................................... 276!
13.2.3 Enabling Watch Items .......................................................................................... 276!
13.2.4 Disabling Watch Items ......................................................................................... 278!
13.2.5 Viewing the Current State of Watch Items ........................................................... 278!
13.3 Deftemplate Commands ................................................................................................ 279!
13.3.1 Displaying the Text of a Deftemplate .................................................................. 279!
13.3.2 Displaying the List of Deftemplates ..................................................................... 279!
13.3.3 Deleting a Deftemplate ......................................................................................... 279!
13.4 Fact Commands ............................................................................................................. 280!
13.4.1 Displaying the Fact-List ....................................................................................... 280!
13.4.2 Loading Facts From a File .................................................................................... 280!
13.4.3 Saving The Fact-List To A File ............................................................................ 280!
13.4.4 Setting the Duplication Behavior of Facts ............................................................ 281!
13.4.5 Getting the Duplication Behavior of Facts ........................................................... 282!
13.4.6 Displaying a Single Fact ....................................................................................... 282!
13.5 Deffacts Commands ...................................................................................................... 283!
13.5.1 Displaying the Text of a Deffacts ......................................................................... 283!
13.5.2 Displaying the List of Deffacts ............................................................................. 283!
13.5.3 Deleting a Deffacts ............................................................................................... 283!
13.6 Defrule Commands ........................................................................................................ 283!
13.6.1 Displaying the Text of a Rule ............................................................................... 284!
13.6.2 Displaying the List of Rules ................................................................................. 284!
13.6.3 Deleting a Defrule ................................................................................................ 284!
13.6.4 Displaying Matches for a Rule ............................................................................. 284!
13.6.5 Setting a Breakpoint for a Rule ............................................................................ 287!
13.6.6 Removing a Breakpoint for a Rule ....................................................................... 287!
13.6.7 Displaying Rule Breakpoints ................................................................................ 288!
13.6.8 Refreshing a Rule ................................................................................................. 288!
13.6.9 Setting the Incremental Reset Behavior ............................................................... 288!
13.6.10 Getting the Incremental Reset Behavior ............................................................. 288!
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13.6.11 Determining the Logical Dependencies of a Pattern Entity ............................... 289!
13.6.12 Determining the Logical Dependents of a Pattern Entity ................................... 289!
13.7 Agenda Commands ....................................................................................................... 289!
13.7.1 Displaying the Agenda ......................................................................................... 290!
13.7.2 Running CLIPS .................................................................................................... 290!
13.7.3 Focusing on a Group of Rules .............................................................................. 290!
13.7.4 Stopping Rule Execution ...................................................................................... 291!
13.7.5 Setting The Current Conflict Resolution Strategy ................................................ 291!
13.7.6 Getting The Current Conflict Resolution Strategy ............................................... 291!
13.7.7 Listing the Module Names on the Focus Stack .................................................... 291!
13.7.8 Removing all Module Names from the Focus Stack ............................................ 292!
13.7.9 Setting the Salience Evaluation Behavior ............................................................ 292!
13.7.10 Getting the Salience Evaluation Behavior .......................................................... 292!
13.7.11 Refreshing the Salience Value of Rules on the Agenda ..................................... 292!
13.8 Defglobal Commands .................................................................................................... 293!
13.8.1 Displaying the Text of a Defglobal ...................................................................... 293!
13.8.2 Displaying the List of Defglobals ......................................................................... 293!
13.8.3 Deleting a Defglobal ............................................................................................. 293!
13.8.4 Displaying the Values of Global Variables .......................................................... 294!
13.8.5 Setting the Reset Behavior of Global Variables ................................................... 294!
13.8.6 Getting the Reset Behavior of Global Variables .................................................. 294!
13.9 Deffunction Commands ................................................................................................. 294!
13.9.1 Displaying the Text of a Deffunction ................................................................... 295!
13.9.2 Displaying the List of Deffunctions ..................................................................... 295!
13.9.3 Deleting a Deffunction ......................................................................................... 295!
13.10 Generic Function Commands ...................................................................................... 295!
13.10.1 Displaying the Text of a Generic Function Header ............................................ 295!
13.10.2 Displaying the Text of a Generic Function Method ........................................... 296!
13.10.3 Displaying the List of Generic Functions ........................................................... 296!
13.10.4 Displaying the List of Methods for a Generic Function ..................................... 296!
13.10.5 Deleting a Generic Function ............................................................................... 296!
13.10.6 Deleting a Generic Function Method ................................................................. 297!
13.10.7 Previewing a Generic Function Call ................................................................... 297!
13.11 CLIPS Object-Oriented Language (COOL) Commands ............................................. 298!
13.11.1 Class Commands ................................................................................................ 298!
13.11.2 Message-handler Commands .............................................................................. 303!
13.11.3 Definstances Commands .................................................................................... 305!
13.11.4 Instances Commands .......................................................................................... 306!
13.12 Defmodule Commands ................................................................................................ 308!
13.12.1 Displaying the Text of a Defmodule .................................................................. 309!
13.12.2 Displaying the List of Defmodules ..................................................................... 309!
13.13 Memory Management Commands .............................................................................. 309!
13.13.1 Determining the Amount of Memory Used by CLIPS ....................................... 309!
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13.13.2 Determining the Number of Memory Requests Made by CLIPS ...................... 309!
13.13.3 Releasing Memory Used by CLIPS ................................................................... 310!
13.13.4 Conserving Memory ........................................................................................... 310!
13.14 External Text Manipulation ......................................................................................... 310!
13.14.1 External Text File Format .................................................................................. 310!
13.14.2 External Text Manipulation Functions ............................................................... 312!
13.15 Profiling Commands .................................................................................................... 315!
13.15.1 Setting the Profiling Report Threshold ............................................................... 315!
13.15.2 Getting the Profiling Report Threshold .............................................................. 315!
13.15.3 Resetting Profiling Information .......................................................................... 315!
13.15.4 Displaying Profiling Information ....................................................................... 316!
13.15.5 Profiling Constructs and User Functions ............................................................ 316!
Appendix A: Support Information ......................................................................................... 319!
A.1 Questions and Information ............................................................................................. 319!
A.2 Documentation ................................................................................................................ 319!
A.3 CLIPS Source Code and Executables ............................................................................. 319!
Appendix B: Update Release Notes ......................................................................................... 321!
B.1 Version 6.30 .................................................................................................................... 321!
B.2 Version 6.24 .................................................................................................................... 322!
B.3 Version 6.23 .................................................................................................................... 324!
B.4 Version 6.22 .................................................................................................................... 325!
B.5 Version 6.21 .................................................................................................................... 325!
B.6 Version 6.2 ...................................................................................................................... 326!
Appendix C: Glossary .............................................................................................................. 329!
Appendix D: Performance Considerations ............................................................................ 339!
D.1 Ordering of Patterns on the LHS .................................................................................... 339!
D.2 Deffunctions versus Generic Functions .......................................................................... 341!
D.3 Ordering of Method Parameter Restrictions ................................................................... 341!
D.4 Instance-Addresses versus Instance-Names ................................................................... 341!
D.5 Reading Instance Slots Directly ..................................................................................... 341!
Appendix E: CLIPS Warning Messages ................................................................................ 343!
Appendix F: CLIPS Error Messages ...................................................................................... 345!
Appendix G: CLIPS BNF ........................................................................................................ 383!
Appendix H: Reserved Function Names ................................................................................ 393!
Appendix I: Bibliography of CLIPS Publications ................................................................. 399!
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Index ........................................................................................................................................... 407!
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License Information
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
associated documentation files (the “Software”), to deal in the Software without restriction,
including without limitation the rights to use, copy, modify, merge, publish, distribute, and/or
sell copies of the Software, and to permit persons to whom the Software is furnished to do so.
THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
PARTICULAR PURPOSE AND NONINFRINGEMENT OF THIRD PARTY RIGHTS. IN NO EVENT SHALL
THE AUTHORS BE LIABLE FOR ANY CLAIM, OR ANY SPECIAL INDIRECT OR CONSEQUENTIAL
DAMAGES, OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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Preface
The History of CLIPS
The origins of the C Language Integrated Production System (CLIPS) date back to 1984 at
NASA’s Johnson Space Center. At this time, the Artificial Intelligence Section had developed
over a dozen prototype expert systems applications using state-of-the-art hardware and software.
However, despite extensive demonstrations of the potential of expert systems, few of these
applications were put into regular use. This failure to provide expert systems technology within
NASA’s operational computing constraints could largely be traced to the use of LISP as the base
language for nearly all expert system software tools at that time. In particular, three problems
hindered the use of LISP based expert system tools within NASA: the low availability of LISP
on a wide variety of conventional computers, the high cost of state-of-the-art LISP tools and
hardware, and the poor integration of LISP with other languages (making embedded applications
difficult).
The Artificial Intelligence Section felt that the use of a conventional language, such as C, would
eliminate most of these problems, and initially looked to the expert system tool vendors to
provide an expert system tool written using a conventional language. Although a number of tool
vendors started converting their tools to run in C, the cost of each tool was still very high, most
were restricted to a small variety of computers, and the projected availability times were
discouraging. To meet all of its needs in a timely and cost effective manner, it became evident
that the Artificial Intelligence Section would have to develop its own C based expert system tool.
The prototype version of CLIPS was developed in the spring of 1985 in a little over two months.
Particular attention was given to making the tool compatible with expert systems under
development at that time by the Artificial Intelligence Section. Thus, the syntax of CLIPS was
made to very closely resemble the syntax of a subset of the ART expert system tool developed
by Inference Corporation. Although originally modelled from ART, CLIPS was developed
entirely without assistance from Inference or access to the ART source code.
The original intent for CLIPS was to gain useful insight and knowledge about the construction of
expert system tools and to lay the groundwork for the construction of a replacement tool for the
commercial tools currently being used. Version 1.0 demonstrated the feasibility of the project
concept. After additional development, it became apparent that CLIPS would be a low cost
expert system tool ideal for the purposes of training. Another year of development and internal
use went into CLIPS improving its portability, performance, functionality, and supporting
documentation. Version 3.0 of CLIPS was made available to groups outside of NASA in the
summer of 1986.
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Preface
Further enhancements transformed CLIPS from a training tool into a tool useful for the
development and delivery of expert systems as well. Versions 4.0 and 4.1 of CLIPS, released
respectively in the summer and fall of 1987, featured greatly improved performance, external
language integration, and delivery capabilities. Version 4.2 of CLIPS, released in the summer of
1988, was a complete rewrite of CLIPS for code modularity. Also included with this release
were an architecture manual providing a detailed description of the CLIPS software architecture
and a utility program for aiding in the verification and validation of rule-based programs.
Version 4.3 of CLIPS, released in the summer of 1989, added still more functionality.
Originally, the primary representation methodology in CLIPS was a forward chaining rule lan-
guage based on the Rete algorithm (hence the Production System part of the CLIPS acronym).
Version 5.0 of CLIPS, released in the spring of 1991, introduced two new programming
paradigms: procedural programming (as found in languages such as C and Ada) and
object-oriented programming (as found in languages such as the Common Lisp Object System
and Smalltalk). The object-oriented programming language provided within CLIPS is called the
CLIPS Object-Oriented Language (COOL). Version 5.1 of CLIPS, released in the fall of 1991,
was primarily a software maintenance upgrade required to support the newly developed and/or
enhanced X Window, MS-DOS, and Macintosh interfaces. Version 6.0 of CLIPS, released in
1993, provided support for the development of modular programs and tight integration between
the object-oriented and rule-based programming capabilities of CLIPS. Version 6.1 of CLIPS,
released in 1998, removed support for older non-ANSI C Compilers and added support for C++
compilers. Commands to profile the time spent in constructs and user-defined functions were
also added. Version 6.2 of CLIPS, released in 2002, added support for multiple environments
into which programs can be loaded and improved Windows XP and MacOS development
interfaces.
Because of its portability, extensibility, capabilities, and low cost, CLIPS has received
widespread acceptance throughout the government, industry, and academia. The development of
CLIPS has helped to improve the ability to deliver expert system technology throughout the
public and private sectors for a wide range of applications and diverse computing environments.
CLIPS is being used by numerous users throughout the public and private community including:
all NASA sites and branches of the military, numerous federal bureaus, government contractors,
universities, and many private companies.
CLIPS is now maintained as public domain software by the main program authors who no longer
work for NASA. See appendix A of the Basic Programming Guide for information on obtaining
CLIPS and support.
CLIPS Version 6.3
Version 6.3 of CLIPS contains one major enhancement (improved rule performance) and several
minor enhancements/changes. For a detailed listing of differences between releases of CLIPS,
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v
refer to appendix B of the Basic Programming Guide and appendix B of the Advanced
Programming Guide.
CLIPS Documentation
Two documents are provided with CLIPS.
• The CLIPS Reference Manual which is split into the following parts:
• Volume I - The Basic Programming Guide, which provides the definitive description of
CLIPS syntax and examples of usage.
• Volume II - The Advanced Programming Guide, which provides detailed discussions of
the more sophisticated features in CLIPS and is intended for people with extensive
programming experience who are using CLIPS for advanced applications.
• Volume III - The Interfaces Guide, which provides information on machine-specific
interfaces.
• The CLIPS User’s Guide which provides an introduction to CLIPS rule-based and
object-oriented programming and is intended for people with little or no expert system
experience.
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Acknowledgements
As with any large project, CLIPS is the result of the efforts of numerous people. The primary
contributors have been: Robert Savely, who conceived the project and provided overall direction
and support; Chris Culbert, who managed the project and wrote the original CLIPS Reference
Manual; Gary Riley, who designed and developed the rule-based portion of CLIPS, co-authored
the CLIPS Reference Manual, and developed the Macintosh interface for CLIPS; Brian Dantes,
who designed and developed the CLIPS Object Oriented Language (COOL) and co-authored the
CLIPS Reference Manual; Bebe Ly, who developed the X Window interface for CLIPS; Chris
Ortiz, who developed the original Windows 95 interface for CLIPS; Dr. Joseph Giarratano of the
University of Houston-Clear Lake, who wrote the CLIPS User’s Guide; and Frank Lopez, who
designed and developed CLIPS version 1.0 and wrote the CLIPS 1.0 User’s Guide.
Many other individuals contributed to the design, development, review, and general support of
CLIPS, including: Jack Aldridge, Carla Colangelo, Paul Baffes, Ann Baker, Stephen
Baudendistel, Les Berke, Tom Blinn, Marlon Boarnet, Dan Bochsler, Bob Brown, Barry
Cameron, Tim Cleghorn, Major Paul Condit, Major Steve Cross, Andy Cunningham, Dan
Danley, Mark Engelberg, Kirt Fields, Ken Freeman, Kevin Greiner, Ervin Grice, Sharon Hecht,
Patti Herrick, Mark Hoffman, Grace Hua, Gordon Johnson, Phillip Johnston, Sam Juliano, Ed
Lineberry, Bowen Loftin, Linda Martin, Daniel McCoy, Terry McGregor, Becky McGuire, Scott
Meadows, C. J. Melebeck, Paul Mitchell, Steve Mueller, Bill Paseman, Cynthia Rathjen, Eric
Raymond, Reza Razavipour, Marsha Renals, Monica Rua, Tim Saito, Michael Sullivan, Gregg
Swietek, Eric Taylor, James Villarreal, Lui Wang, Bob Way, Jim Wescott, Charlie Wheeler, and
Wes White.
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Section 1:
Introduction
This manual is the Basic Programming Guide for CLIPS. It is intended for users interested in the
syntax of CLIPS. No previous expert system background is required, although a general
understanding of computer languages is assumed. Section 2 of this manual provides an overview
of the CLIPS language and basic terminology. Sections 3 through 11 provide additional details
regarding the CLIPS programming language on topics such as rules and the CLIPS Object
Oriented Programming Language (COOL). The types of actions and functions provided by
CLIPS are defined in section 12. Finally, commands typically used from the CLIPS interactive
interface are described in section 13.
The Basic Programming Guide documents just the basic CLIPS syntax. More advanced
capabilities, such as user-defined functions, embedded applications, etc., are documented more
fully in the Advanced Programming Guide. The Advanced Programming Guide is intended for
users who have a complete knowledge of the CLIPS syntax and a programming background. It is
not necessary to read the Advanced Programming Guide to learn how to use CLIPS. CLIPS can
be learned and simple expert systems can be built with the information provided in this manual.
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Section 2:
CLIPS Overview
This section gives a general overview of CLIPS and of the basic concepts used throughout this
manual.
2.1 Interacting with CLIPS
CLIPS expert systems may be executed in three ways: interactively using a simple, text-oriented,
command prompt interface; interactively using a window/menu/mouse interface on certain ma-
chines; or as embedded expert systems in which the user provides a main program and controls
execution of the expert system. Embedded applications are discussed in the Advanced
Programming Guide. In addition, a series of commands can be automatically read directly from a
file when CLIPS is first started or as the result of the batch command.
The generic CLIPS interface is a simple, interactive, text-oriented, command prompt interface
for high portability. The standard usage is to create or edit a knowledge base using any standard
text editor, save the knowledge base as one or more text files, exit the editor and execute CLIPS,
then load the knowledge base into CLIPS. The interface provides commands for viewing the
current state of the system, tracing execution, adding or removing information, and clearing
CLIPS.
A more sophisticated window interface is available for the Macintosh, Windows 3.1, and X
Window environments. All interface commands described in this section are available in the
window interfaces. These interfaces are described in more detail in the Interfaces Guide.
2.1.1 Top Level Commands
The primary method for interacting with CLIPS in a non-embedded environment is through the
CLIPS command prompt (or top level). When the “CLIPS>” prompt is printed, a command
may be entered for evaluation. Commands may be function calls, constructs, local or global
variables, or constants. If a function call is entered (see section 2.3.2), that function is evaluated
and its return value is printed. Function calls in CLIPS use a prefix notation—the operands to a
function always appear after the function name. Entering a construct definition (see section
2.3.3) at the CLIPS prompt creates a new construct of the appropriate type. Entering a global
variable (see section 2.4.3) causes the value of the global variable to be printed. Local variables
can be set at the command prompt using the bind function and retain their value until a reset or
clear command is issued. Entering a local variable at the command prompt causes the value of
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Section 2: CLIPS Overview
the local variable to be printed. Entering a constant (see section 2.3.1) at the top level causes the
constant to be printed (which is not very useful). For example,
CLIPS (V6.30 3/11/15)
CLIPS> (+ 3 4)
7
CLIPS> (defglobal ?*x* = 3)
CLIPS> ?*x*
3
CLIPS> red
red
CLIPS> (bind ?a 5)
5
CLIPS> (+ ?a 3)
8
CLIPS> (reset)
CLIPS> ?a
[EVALUATN1] Variable a is unbound
FALSE
CLIPS>
The previous example first called the addition function adding the numbers 3 and 4 to yield the
result 7. A global variable ?*x* was then defined and given the value 3. The variable ?*x* was
then entered at the prompt and its value of 3 was returned. Finally the constant symbol red was
entered and was returned (since a constant evaluates to itself).
2.1.2 Automated Command Entry and Loading
Some operating systems allow additional arguments to be specified to a program when it begins
execution. When the CLIPS executable is started under such an operating system, CLIPS can be
made to automatically execute a series of commands read directly from a file or to load
constructs from a file. The command-line syntax for starting CLIPS and automatically reading
commands or loading constructs from a file is as follows:
Syntax
clips <option>*
<option> ::= -f <filename> |
-f2 <filename> |
-l <filename>
For the -f option, <filename> is a file that contains CLIPS commands. If the exit command is
included in the file, CLIPS will halt and the user is returned to the operating system after
executing the commands in the file. If an exit command is not in the file, CLIPS will enter in its
interactive state after executing the commands in the file. Commands in the file should be
entered exactly as they would be interactively (i.e. opening and closing parentheses must be
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CLIPS Basic Programming Guide
5
included and a carriage return must be at the end of the command). The -f command line option
is equivalent to interactively entering a batch command as the first command to the CLIPS
prompt.
The -f2 option is similar to the -f option, but is equivalent to interactively entering a batch*
command. The commands stored in <filename> are immediately executed, but the commands
and their return values are not displayed as they would be for a batch command.
For the -l option, <filename> should be a file containing CLIPS constructs. This file will be
loaded into the environment. The -l command line option is equivalent to interactively entering a
load command.
2.1.3 Integration with Other Programming Languages
When using an expert system, two kinds of integration are important: embedding CLIPS in other
systems, and calling external functions from CLIPS. CLIPS was designed to allow both kinds of
integration.
Using CLIPS as an embedded application allows the easy integration of CLIPS with existing
systems. This is useful in cases where the expert system is a small part of a larger task or needs
to share data with other functions. In these situations, CLIPS can be called as a subroutine and
information may be passed to and from CLIPS. Embedded applications are discussed in the
Advanced Programming Guide.
It also may be useful to call external functions while executing a CLIPS construct or from the
top-level of the interactive interface. CLIPS variables or literal values may be passed to an
external function, and functions may return values to CLIPS. The easy addition of external
functions allows CLIPS to be extended or customized in almost any way. The Advanced
Programming Guide describes how to integrate CLIPS with functions or systems written in C as
well as in other languages.
2.2 Reference Manual Syntax
The terminology used throughout this manual to describe the CLIPS syntax is fairly common to
computer reference manuals. Plain words or characters, particularly parentheses, are to be typed
exactly as they appear. Bolded words or characters, however, represent a verbal description of
what is to be entered. Sequences of words enclosed in single-angle brackets (called terms or
non-terminal symbols), such as <string>, represent a single entity of the named class of items to
be supplied by the user. A non-terminal symbol followed by a *, represents zero or more entities
of the named class of items which must be supplied by the user. A non-terminal symbol followed
by a +, represents one or more entities of the named class of items which must be supplied by the
user. A * or + by itself is to be typed as it appears. Vertical and horizontal ellipsis (three dots
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Section 2: CLIPS Overview
arranged respectively vertically and horizontally) are also used between non-terminal symbols to
indicate the occurrence of one or more entities. A term enclosed within square brackets, such as
[<comment>], is optional (i.e. it may or may not be included). Vertical bars indicate a choice
between multiple terms. White spaces (tabs, spaces, carriage returns) are used by CLIPS only as
delimiters between terms and are ignored otherwise (unless inside double quotes). The ::=
symbol is used to indicate how a non-terminal symbol can be replaced. For example, the
following syntax description indicates that a <lexeme> can be replaced with either a <symbol>
or a <string>.
<lexeme> ::= <symbol> | <string>
A complete BNF listing for CLIPS constructs along with some commonly used replacements for
non-terminal symbols are listed in appendix G.
2.3 Basic Programming Elements
CLIPS provides three basic elements for writing programs: primitive data types, functions for
manipulating data, and constructs for adding to a knowledge base.
2.3.1 Data Types
CLIPS provides eight primitive data types for representing information. These types are float,
integer, symbol, string, external-address, fact-address, instance-name and instance-address.
Numeric information can be represented using floats and integers. Symbolic information can be
represented using symbols and strings.
A number consists only of digits (0-9), a decimal point (.), a sign (+ or -), and, optionally, an (e)
for exponential notation with its corresponding sign. A number is either stored as a float or an
integer. Any number consisting of an optional sign followed by only digits is stored as an
integer (represented internally by CLIPS as a C long integer). All other numbers are stored as
floats (represented internally by CLIPS as a C double-precision float). The number of significant
digits will depend on the machine implementation. Roundoff errors also may occur, again
depending on the machine implementation. As with any computer language, care should be taken
when comparing floating-point values to each other or comparing integers to floating-point
values. Some examples of integers are
237 15 +12 -32
Some examples of floats are
237e3 15.09 +12.0 -32.3e-7
Specifically, integers use the following format:
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<integer> ::= [+ | -] <digit>+
<digit> ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
Floating point numbers use the following format:
<float> ::= <integer> <exponent> |
<integer> . [exponent]
. <unsigned integer> [exponent]
<integer> . <unsigned integer> [exponent]
<unsigned-integer> ::= <digit>+
<exponent> ::= e | E <integer>
A sequence of characters which does not exactly follow the format of a number is treated as a
symbol (see the next paragraph).
A symbol in CLIPS is any sequence of characters that starts with any printable ASCII character
and is followed by zero or more printable ASCII characters. When a delimiter is found, the
symbol is ended. The following characters act as delimiters: any non-printable ASCII character
(including spaces, tabs, carriage returns, and line feeds), a double quote, opening and closing
parentheses “(” and “)”, an ampersand “&”, a vertical bar “|”, a less than “<”, and a tilde “~”. A
semicolon “;” starts a CLIPS comment (see section 2.3.3) and also acts as a delimiter. Delimiters
may not be included in symbols with the exception of the “<“ character which may be the first
character in a symbol. In addition, a symbol may not begin with either the “?” character or the
“$?” sequence of characters (although a symbol may contain these characters). These characters
are reserved for variables (which are discussed later in this section). CLIPS is case sensitive (i.e.
uppercase letters will match only uppercase letters). Note that numbers are a special case of
symbols (i.e. they satisfy the definition of a symbol, but they are treated as a different data type).
Some simple examples of symbols are
foo Hello B76-HI bad_value
127A 456-93-039 @+=-% 2each
A string is a set of characters that starts with a double quote (") and is followed by zero or more
printable characters. A string ends with double quotes. Double quotes may be embedded within a
string by placing a backslash (\) in front of the character. A backslash may be embedded by
placing two consecutive backslash characters in the string. Some examples are
"foo" "a and b" "1 number" "a\"quote"
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Section 2: CLIPS Overview
Note that the string “abcd" is not the same as the symbol abcd. They both contain the same
characters, but are of different types. The same holds true for the instance name [abcd].
An external-address is the address of an external data structure returned by a function (written
in a language such as C or Ada) that has been integrated with CLIPS. This data type can only be
created by calling a function (i.e. it is not possible to specify an external-address by typing the
value). In the basic version of CLIPS (which has no user defined external functions), it is not
possible to create this data type. External-addresses are discussed in further detail in the
Advanced Programming Guide. Within CLIPS, the printed representation of an external-address
is
<Pointer-XXXXXX>
where XXXXXX is the external-address.
A fact is a list of atomic values that are either referenced positionally (ordered facts) or by name
(non-ordered or template facts). Facts are referred to by index or address; section 2.4.1 gives
more details. The printed format of a fact-address is:
<Fact-XXX>
where XXX is the fact-index.
An instance is an object that is an instantiation or specific example of a class. Objects in CLIPS
are defined to be floats, integers, symbols, strings, multifield values, external-addresses,
fact-addresses or instances of a user-defined class. A user-defined class is created using the
defclass construct. An instance of a user-defined class is created with the make-instance
function, and such an instance can be referred to uniquely by address. Within the scope of a
module (see section 10.5.1), an instance can also be uniquely referred to by name. All of these
definitions will be covered in more detail in Sections 2.4.2, 2.5.2.3, 2.6 and 9. An instance-name
is formed by enclosing a symbol within left and right brackets. Thus, pure symbols may not be
surrounded by brackets. If the CLIPS Object Oriented Language (COOL) is not included in a
particular CLIPS configuration, then brackets may be wrapped around symbols. Some examples
of instance-names are:
[pump-1] [foo] [+++] [123-890]
Note that the brackets are not part of the name of the instance; they merely indicate that the
enclosed symbol is an instance-name. An instance-address can only be obtained by binding the
return value of a function called instance-address or by binding a variable to an instance
matching an object pattern on the LHS of a rule (i.e., it is not possible to specify an
instance-address by typing the value). A reference to an instance of a user-defined class can
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CLIPS Basic Programming Guide
9
either be by name or address; instance-addresses should only be used when speed is critical.
Within CLIPS, the printed representation of an instance-address is
<Instance-XXX>
where XXX is the name of the instance.
In CLIPS, a placeholder that has a value (one of the primitive data types) is referred to as a field.
The primitive data types are referred to as single-field values. A constant is a non-varying
single field value directly expressed as a series of characters (which means that
external-addresses, fact-addresses and instance-addresses cannot be expressed as constants
because they can only be obtained through function calls and variable bindings). A multifield
value is a sequence of zero or more single field values. When displayed by CLIPS, multifield
values are enclosed in parentheses. Collectively, single and multifield values are referred to as
values. Some examples of multifield values are
(a) (1 bar foo) () (x 3.0 "red" 567)
Note that the multifield value (a) is not the same as the single field value a. Multifield values are
created either by calling functions which return multifield values, by using wildcard arguments
in a deffunction, object message-handler, or method, or by binding variables during the
pattern-matching process for rules. In CLIPS, a variable is a symbolic location that is used to
store values. Variables are used by many of the CLIPS constructs (such as defrule, deffunction,
defmethod, and defmessage-handler) and their usage is explained in the sections describing each
of these constructs.
2.3.2 Functions
A function in CLIPS is a piece of executable code identified by a specific name which returns a
useful value or performs a useful side effect (such as displaying information). Throughout the
CLIPS documentation, the word function is generally used to refer only to functions which
return a value (whereas commands and actions are used to refer to functions which have a side
effect but generally do not return a value).
There are several types of functions. User defined functions and system defined functions are
pieces of code that have been written in an external language (such as C, FORTRAN, or Ada)
and linked with the CLIPS environment. System defined functions are those functions that have
been defined internally by the CLIPS environment. User defined functions are functions that
have been defined externally of the CLIPS environment. A complete list of system defined
functions can be found in appendix H.
The deffunction construct allows users to define new functions directly in the CLIPS
environment using CLIPS syntax. Functions defined in this manner appear and act like other
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Section 2: CLIPS Overview
functions, however, instead of being directly executed (as code written in an external language
would be) they are interpreted by the CLIPS environment. Deffunctions are also discussed in
section 2.5.2.1 in the context of procedural knowledge representation.
Generic functions can be defined using the defgeneric and defmethod constructs. Generic
functions allow different pieces of code to be executed depending upon the arguments passed to
the generic function. Thus, a single function name can be overloaded with more than one piece
of code. Generic functions are also discussed in section 2.5.2.2 in the context of procedural
knowledge representation.
Function calls in CLIPS use a prefix notation – the arguments to a function always appear after
the function name. Function calls begin with a left parenthesis, followed by the name of the
function, then the arguments to the function follow (each argument separated by one or more
spaces). Arguments to a function can be primitive data types, variables, or another function call.
The function call is then closed with a right parenthesis. Some examples of function calls using
the addition (+) and multiplication (*) functions are shown following.
(+ 3 4 5)
(* 5 6.0 2)
(+ 3 (* 8 9) 4)
(* 8 (+ 3 (* 2 3 4) 9) (* 3 4))
While a function refers to a piece of executable code identified by a specific name, an
expression refers to a function which has its arguments specified (which may or may not be
functions calls as well). Thus the previous examples are expressions which make calls to the *
and + functions.
2.3.3 Constructs
Several defining constructs appear in CLIPS: defmodule, defrule, deffacts, deftemplate,
defglobal, deffunction, defclass, definstances, defmessage-handler, defgeneric, and
defmethod. All constructs in CLIPS are surrounded by parentheses. The construct opens with a
left parenthesis and closes with a right parenthesis. Defining a construct differs from calling a
function primarily in effect. Typically a function call leaves the CLIPS environment unchanged
(with some notable exceptions such as resetting or clearing the environment or opening a file).
Defining a construct, however, is explicitly intended to alter the CLIPS environment by adding
to the CLIPS knowledge base. Unlike function calls, constructs never have a return value.
As with any programming language, it is highly beneficial to comment CLIPS code. All
constructs (with the exception of defglobal) allow a comment directly following the construct
name. Comments also can be placed within CLIPS code by using a semicolon (;). Everything
from the semicolon until the next return character will be ignored by CLIPS. If the semicolon is
the first character in the line, the entire line will be treated as a comment. Examples of
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commented code will be provided throughout the reference manual. Semicolon commented text
is not saved by CLIPS when loading constructs (however, the optional comment string within a
construct is saved).
2.4 Data Abstraction
There are three primary formats for representing information in CLIPS: facts, objects and global
variables.
2.4.1 Facts
Facts are one of the basic high-level forms for representing information in a CLIPS system. Each
fact represents a piece of information that has been placed in the current list of facts, called the
fact-list. Facts are the fundamental unit of data used by rules (see section 2.5.1).
Facts may be added to the fact-list (using the assert command), removed from the fact-list (using
the retract command), modified (using the modify command), or duplicated (using the
duplicate command) through explicit user interaction or as a CLIPS program executes. The
number of facts in the fact-list and the amount of information that can be stored in a fact is
limited only by the amount of memory in the computer. If a fact is asserted into the fact-list that
exactly matches an already existing fact, the new assertion will be ignored (however, this
behavior can be changed, see sections 13.4.4 and 13.4.5).
Some commands, such as the retract, modify, and duplicate commands, require a fact to be
specified. A fact can be specified either by fact-index or fact-address. Whenever a fact is added
(or modified) it is given a unique integer index called a fact-index. Fact-indices start at zero and
are incremented by one for each new or changed fact. Whenever a reset or clear command is
given, the fact-indices restart at zero. A fact may also be specified through the use of a
fact-address. A fact-address can be obtained by capturing the return value of commands which
return fact addresses (such as assert, modify, and duplicate) or by binding a variable to the fact
address of a fact which matches a pattern on the LHS of a rule (see section 5.4.1.8 for details).
A fact identifier is a shorthand notation for displaying a fact. It consists of the character “f”,
followed by a dash, followed by the fact-index of the fact. For example, f-10 refers to the fact
with fact-index 10.
A fact is stored in one of two formats: ordered or non-ordered.
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2.4.1.1 Ordered Facts
Ordered facts consist of a symbol followed by a sequence of zero or more fields separated by
spaces and delimited by an opening parenthesis on the left and a closing parenthesis on the right.
The first field of an ordered fact specifies a “relation” that applied to the remaining fields in the
ordered fact. For example, (father-of jack bill) states that bill is the father of jack.
Some examples of ordered facts are shown following.
(the pump is on)
(altitude is 10000 feet)
(grocery-list bread milk eggs)
Fields in a non-ordered fact may be of any of the primitive data types (with the exception of the
first field which must be a symbol), and no restriction is placed on the ordering of fields. The
following symbols are reserved and should not be used as the first field in any fact (ordered or
non-ordered): test, and, or, not, declare, logical, object, exists, and forall. These words are
reserved only when used as a deftemplate name (whether explicitly defined or implied). These
symbols may be used as slot names, however, this is not recommended.
2.4.1.2 Non-ordered Facts
Ordered facts encode information positionally. To access that information, a user must know not
only what data is stored in a fact but which field contains the data. Non-ordered (or
deftemplate) facts provide the user with the ability to abstract the structure of a fact by assign-
ing names to each field in the fact. The deftemplate construct (see section 3) is used to create a
template that can then be used to access fields by name. The deftemplate construct is analogous
to a record or structure definition in programming languages such as Pascal and C.
The deftemplate construct allows the name of a template to be defined along with zero or more
definitions of named fields or slots. Unlike ordered facts, the slots of a deftemplate fact may be
constrained by type, value, and numeric range. In addition, default values can be specified for a
slot. A slot consists of an opening parenthesis followed by the name of the slot, zero or more
fields, and a closing parenthesis. Note that slots may not be used in an ordered fact and that
positional fields may not be used in a deftemplate fact.
Deftemplate facts are distinguished from ordered facts by the first field within the fact. The first
field of all facts must be a symbol, however, if that symbol corresponds to the name of a
deftemplate, then the fact is a deftemplate fact. The first field of a deftemplate fact is followed by
a list of zero or more slots. As with ordered facts, deftemplate facts are enclosed by an opening
parenthesis on the left and a closing parenthesis on the right.
Some examples of deftemplate facts are shown following.
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(client (name "Joe Brown") (id X9345A))
(point-mass (x-velocity 100) (y-velocity -200))
(class (teacher "Martha Jones") (#-students 30) (Room "37A"))
(grocery-list (#-of-items 3) (items bread milk eggs))
Note that the order of slots in a deftemplate fact is not important. For example the following facts
are all identical:
(class (teacher "Martha Jones") (#-students 30) (Room "37A"))
(class (#-students 30) (teacher "Martha Jones") (Room "37A"))
(class (Room "37A") (#-students 30) (teacher "Martha Jones"))
In contrast, note that the following ordered fact are not identical.
(class "Martha Jones" 30 "37A")
(class 30 "Martha Jones" "37A")
(class "37A" 30 "Martha Jones")
The immediate advantages of clarity and slot order independence for deftemplate facts should be
readily apparent.
In addition to being asserted and retracted, deftemplate facts can also be modified and duplicated
(using the modify and duplicate commands). Modifying a fact changes a set of specified slots
within that fact. Duplicating a fact creates a new fact identical to the original fact and then
changes a set of specified slots within the new fact. The benefit of using the modify and
duplicate commands is that slots which don’t change, don’t have to be specified.
2.4.1.3 Initial Facts
The deffacts construct allows a set of a priori or initial knowledge to be specified as a collection
of facts. When the CLIPS environment is reset (using the reset command) every fact specified
within a deffacts construct in the CLIPS knowledge base is added to the fact-list.
2.4.2 Objects
An object in CLIPS is defined to be a symbol, a string, a floating-point or integer number, a
multifield value, an external-address or an instance of a user-defined class. Section 2.3.1 explains
how to reference instances of user-defined classes. Objects are described in two basic parts:
properties and behavior. A class is a template for common properties and behavior of objects that
are instances of that class. Some examples of objects and their classes are:
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Object (Printed Representation)
Class
Rolls-Royce
SYMBOL
"Rolls-Royce"
STRING
8.0
FLOAT
8
INTEGER
(8.0 Rolls-Royce 8 [Rolls-Royce])
MULTIFIELD
<Pointer-00CF61AB>
EXTERNAL-ADDRESS
[Rolls-Royce]
CAR (a user-defined class)
Objects in CLIPS are split into two important categories: primitive types and instances of
user-defined classes. These two types of objects differ in the way they are referenced, created
and deleted as well as how their properties are specified.
Primitive type objects are referenced simply by giving their value, and they are created and
deleted implicitly by CLIPS as they are needed. Primitive type objects have no names or slots,
and their classes are predefined by CLIPS. The behavior of primitive type objects is like that of
instances of user-defined classes, however, in that you can define message-handlers and attach
them to the primitive type classes. It is anticipated that primitive types will not be used often in
an object-oriented programming (OOP) context; the main reason classes are provided for them is
for use in generic functions. Generic functions use the classes of their arguments to determine
which methods to execute; sections 2.3.2, 2.5.2.2 and 8 give more detail.
An instance of a user-defined class is referenced by name or address, and they are created and
deleted explicitly via messages and special functions. The properties of an instance of a
user-defined class are expressed by a set of slots, which the object obtains from its class. As
previously defined, slots are named single field or multifield values. For example, the object
Rolls-Royce is an instance of the class CAR. One of the slots in class CAR might be “price”, and
the Rolls-Royce object’s value for this slot might be $75,000.00. The behavior of an object is
specified in terms of procedural code called message-handlers, which are attached to the object’s
class. Message-handlers and manipulation of objects are described in Section 2.5.2.3. All
instances of a user-defined class have the same set of slots, but each instance may have different
values for those slots. However, two instances that have the same set of slots do not necessarily
belong to the same class, since two different classes can have identical sets of slots.
The primary difference between object slots and template (or non-ordered) facts is the notion of
inheritance. Inheritance allows the properties and behavior of a class to be described in terms of
other classes. COOL supports multiple inheritance: a class may directly inherit slots and
message-handlers from more than one class. Since inheritance is only useful for slots and
message-handlers, it is often not meaningful to inherit from one of the primitive type classes,
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such as MULTIFIELD or NUMBER. This is because these classes cannot have slots and usually
do not have message-handlers.
Further discussion on these topics can be found in Section 2.6, and a comprehensive description
of the CLIPS Object-Oriented Language (COOL) can be found in Section 9.
2.4.2.1 Initial Objects
The definstances construct allows a set of a priori or initial knowledge to be specified as a
collection of instances of user-defined classes. When the CLIPS environment is reset (using the
reset command) every instance specified within a definstances construct in the CLIPS
knowledge base is added to the instance-list.
2.4.3 Global Variables
The defglobal construct allows variables to be defined which are global in scope throughout the
CLIPS environment. That is, a global variable can be accessed anywhere in the CLIPS
environment and retains its value independent of other constructs. In contrast, some constructs
(such as defrule and deffunction) allow local variables to be defined within the definition of the
construct. These local variables can be referred to within the construct, but have no meaning
outside the construct. A CLIPS global variable is similar to global variables found in procedural
programming languages such as LISP, C and Ada. Unlike C and Ada, however, CLIPS global
variables are weakly typed (they are not restricted to holding a value of a single data type).
2.5 Knowledge Representation
CLIPS provides heuristic and procedural paradigms for representing knowledge. These two
paradigms are discussed in this section. Object-oriented programming (which combines aspects
of both data abstraction and procedural knowledge) is discussed in section 2.6.
2.5.1 Heuristic Knowledge – Rules
One of the primary methods of representing knowledge in CLIPS is a rule. Rules are used to
represent heuristics, or “rules of thumb”, which specify a set of actions to be performed for a
given situation. The developer of an expert system defines a set of rules that collectively work
together to solve a problem. A rule is composed of an antecedent and a consequent. The
antecedent of a rule is also referred to as the if portion or the left-hand side (LHS) of the rule.
The consequent of a rule is also referred to as the then portion or the right-hand side (RHS) of
the rule.
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The antecedent of a rule is a set of conditions (or conditional elements) that must be satisfied
for the rule to be applicable. In CLIPS, the conditions of a rule are satisfied based on the
existence or non-existence of specified facts in the fact-list or specified instances of user-defined
classes in the instance-list. One type of condition that can be specified is a pattern. Patterns
consist of a set of restrictions that are used to determine which facts or objects satisfy the
condition specified by the pattern. The process of matching facts and objects to patterns is called
pattern-matching. CLIPS provides a mechanism, called the inference engine, which
automatically matches patterns against the current state of the fact-list and instance-list and
determines which rules are applicable.
The consequent of a rule is the set of actions to be executed when the rule is applicable. The
actions of applicable rules are executed when the CLIPS inference engine is instructed to begin
execution of applicable rules. If more than one rule is applicable, the inference engine uses a
conflict resolution strategy to select which rule should have its actions executed. The actions of
the selected rule are executed (which may affect the list of applicable rules) and then the
inference engine selects another rule and executes its actions. This process continues until no
applicable rules remain.
In many ways, rules can be thought of as IF-THEN statements found in procedural programming
languages such as C and Ada. However, the conditions of an IF-THEN statement in a procedural
language are only evaluated when the program flow of control is directly at the IF-THEN
statement. In contrast, rules act like WHENEVER-THEN statements. The inference engine
always keeps track of rules that have their conditions satisfied and thus rules can immediately be
executed when they are applicable. In this sense, rules are similar to exception handlers found in
languages such as Ada.
2.5.2 Procedural Knowledge
CLIPS also supports a procedural paradigm for representing knowledge like that of more
conventional languages, such as Pascal and C. Deffunctions and generic functions allow the user
to define new executable elements to CLIPS that perform a useful side-effect or return a useful
value. These new functions can be called just like the built-in functions of CLIPS.
Message-handlers allow the user to define the behavior of objects by specifying their response to
messages. Deffunctions, generic functions and message-handlers are all procedural pieces of
code specified by the user that CLIPS executes interpretively at the appropriate times.
Defmodules allow a knowledge base to be partitioned.
2.5.2.1 Deffunctions
Deffunctions allow you to define new functions in CLIPS directly. In previous versions of
CLIPS, the only way to have user-defined functions was to write them in some external
language, such as C or Ada, and then recompile and relink CLIPS with the new functions. The
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body of a deffunction is a series of expressions similar to the RHS of a rule that are executed in
order by CLIPS when the deffunction is called. The return value of a deffunction is the value of
the last expression evaluated within the deffunction. Calling a deffunction is identical to calling
any other function in CLIPS. Deffunctions are covered comprehensively in Section 7.
2.5.2.2 Generic Functions
Generic functions are similar to deffunctions in that they can be used to define new procedural
code directly in CLIPS, and they can be called like any other function. However, generic
functions are much more powerful because they can be overloaded. A generic function will do
different things depending on the types (or classes) and number of its arguments. Generic
functions are comprised of multiple components called methods, where each method handles
different cases of arguments for the generic function. For example, you might overload the “+”
operator to do string concatenation when it is passed strings as arguments. However, the “+”
operator will still perform arithmetic addition when passed numbers. There are two methods in
this example: an explicit one for strings defined by the user and an implicit one which is the
standard CLIPS arithmetic addition operator. The return value of a generic function is the
evaluation of the last expression in the method executed. Generic functions are covered
comprehensively in Section 8.
2.5.2.3 Object Message-Passing
Objects are described in two basic parts: properties and behavior. Object properties are specified
in terms of slots obtained from the object’s class; slots are discussed in more detail in Section
2.4.2. Object behavior is specified in terms of procedural code called message-handlers which
are attached to the object’s class. Objects are manipulated via message-passing. For example, to
cause the Rolls-Royce object, which is an instance of the class CAR, to start its engine, the user
must call the send function to send the message “start-engine” to the Rolls-Royce. How the
Rolls-Royce responds to this message will be dictated by the execution of the message-handlers
for “start-engine” attached to the CAR class and any of its superclasses. The result of a message
is similar to a function call in CLIPS: a useful return value or side-effect.
Further discussion on message-handlers can be found in Section 2.6, and a comprehensive
description of the CLIPS Object-Oriented Language (COOL) can be found in Section 9.
2.5.2.4 Defmodules
Defmodules allow a knowledge base to be partitioned. Every construct defined must be placed in
a module. The programmer can explicitly control which constructs in a module are visible to
other modules and which constructs from other modules are visible to a module. The visibility of
facts and instances between modules can be controlled in a similar manner. Modules can also be
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used to control the flow of execution of rules. Defmodules are covered comprehensively in
Section 10.
2.6 CLIPS Object-Oriented Language
This section gives a brief overview of the programming elements of the CLIPS Object-Oriented
Language (COOL). COOL includes elements of data abstraction and knowledge representation.
This section gives an overview of COOL as a whole, incorporating the elements of both
concepts. References to instanes of user-defined classes are discussed in Section 2.3.1, and the
structure of objects is discussed in Sections 2.4.2 and 2.5.2.3. The comprehensive details of
COOL are given in Section 9.
2.6.1 COOL Deviations from a Pure OOP Paradigm
In a pure OOP language, all programming elements are objects which can only be manipulated
via messages. In CLIPS, the definition of an object is much more constrained: floating-point and
integer numbers, symbols, strings, multifield values, external-addresses, fact-addresses and
instances of user-defined classes. All objects may be manipulated with messages, except
instances of user-defined classes, which must be. For example, in a pure OOP system, to add two
numbers together, you would send the message “add” to the first number object with the second
number object as an argument. In CLIPS, you may simply call the “+” function with the two
numbers as arguments, or you can define message-handlers for the NUMBER class which allow
you to do it in the purely OOP fashion.
All programming elements that are not objects must be manipulated in a non-OOP utilizing
function tailored for those programming elements. For example, to print a rule, you call the
function ppdefrule; you do not send a message “print” to a rule, since it is not an object.
2.6.2 Primary OOP Features
There are five primary characteristics that an OOP system must possess: abstraction,
encapsulation, inheritance, polymorphism and dynamic binding. An abstraction is a higher
level, more intuitive representation for a complex concept. Encapsulation is the process whereby
the implementation details of an object are masked by a well-defined external interface. Classes
may be described in terms of other classes by use of inheritance. Polymorphism is the ability of
different objects to respond to the same message in a specialized manner. Dynamic binding is the
ability to defer the selection of which specific message-handlers will be called for a message
until run-time.
The definition of new classes allows the abstraction of new data types in COOL. The slots and
message-handlers of these classes describe the properties and behavior of a new group of objects.
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COOL supports encapsulation by requiring message-passing for the manipulation of instances of
user-defined classes. An instance cannot respond to a message for which it does not have a
defined message-handler.
COOL allows the user to specify some or all of the properties and behavior of a class in terms of
one or more unrelated superclasses. This process is called multiple inheritance. COOL uses the
existing hierarchy of classes to establish a linear ordering called the class precedence list for a
new class. Objects that are instances of this new class can inherit properties (slots) and behavior
(message-handlers) from each of the classes in the class precedence list. The word precedence
implies that properties and behavior of a class first in the list override conflicting definitions of a
class later in the list.
One COOL object can respond to a message in a completely different way than another object;
this is polymorphism. This is accomplished by attaching message-handlers with differing actions
but which have the same name to the classes of these two objects respectively.
Dynamic binding is supported in that an object reference (see section 2.3.1) in a send function
call is not bound until run-time. For example, an instance-name or variable might refer to one
object at the time a message is sent and another at a later time.
2.6.3 Instance-set Queries and Distributed Actions
In addition to the ability of rules to directly pattern-match on objects, COOL provides a useful
query system for determining, grouping and performing actions on sets of instances of
user-defined classes that meet user-defined criteria. The query system allows you to associate
instances that are either related or not. You can simply use the query system to determine if a
particular association set exists, you can save the set for future reference, or you can iterate an
action over the set. An example of the use of the query system might be to find the set of all pairs
of boys and girls that have the same age.
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Section 3:
Deftemplate Construct
Ordered facts encode information positionally. To access that information, a user must know not
only what data is stored in a fact but also which field contains the data. Non-ordered (or
deftemplate) facts provide the user with the ability to abstract the structure of a fact by assigning
names to each field found within the fact. The deftemplate construct is used to create a template
that can then be used by non-ordered facts to access fields of the fact by name. The deftemplate
construct is analogous to a record or structure definition in programming languages such as
Pascal and C.
Syntax
(deftemplate <deftemplate-name> [<comment>]
<slot-definition>*)
<slot-definition> ::= <single-slot-definition> |
<multislot-definition>
<single-slot-definition>
::= (slot <slot-name>
<template-attribute>*)
<multislot-definition>
::= (multislot <slot-name>
<template-attribute>*)
<template-attribute> ::= <default-attribute> |
<constraint-attribute>
<default-attribute>
::= (default ?DERIVE | ?NONE | <expression>*) |
(default-dynamic <expression>*)
Redefining a deftemplate will result in the previous definition being discarded. A deftemplate
can not be redefined while it is being used (for example, by a fact or pattern in a rule). A
deftemplate can have any number of single or multifield slots. CLIPS always enforces the single
and multifield definitions of the deftemplate. For example, it is an error to store (or match)
multiple values in a single-field slot.
Example
(deftemplate object
(slot name)
(slot location)
(slot on-top-of)
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(slot weight)
(multislot contents))
3.1 Slot Default Values
The <default-attribute> specifies the value to be used for unspecified slots of a template fact
when an assert action is performed. One of two types of default selections can be chosen: default
or dynamic-default.
The default attribute specifies a static default value. The specified expressions are evaluated
once when the deftemplate is defined and the result is stored with the deftemplate. The result is
assigned to the appropriate slot when a new template fact is asserted. If the keyword ?DERIVE is
used for the default value, then a default value is derived from the constraints for the slot (see
section 11.5 for more details). By default, the default attribute for a slot is (default ?DERIVE). If
the keyword ?NONE is used for the default value, then a value must explicitly be assigned for a
slot when an assert is performed. It is an error to assert a template fact without specifying the
values for the (default ?NONE) slots.
The default-dynamic attribute is a dynamic default. The specified expressions are evaluated
every time a template fact is asserted, and the result is assigned to the appropriate slot.
A single-field slot may only have a single value for its default. Any number of values may be
specified as the default for a multifield slot (as long as the number of values satisfies the
cardinality attribute for the slot).
Example
CLIPS> (clear)
CLIPS>
(deftemplate foo
(slot w (default ?NONE))
(slot x (default ?DERIVE))
(slot y (default (gensym*)))
(slot z (default-dynamic (gensym*))))
CLIPS> (assert (foo))
[TMPLTRHS1] Slot w requires a value because of its (default ?NONE) attribute.
CLIPS> (assert (foo (w 3)))
<Fact-1>
CLIPS> (assert (foo (w 4)))
<Fact-2>
CLIPS> (facts)
f-0 (initial-fact)
f-1 (foo (w 3) (x nil) (y gen1) (z gen2))
f-2 (foo (w 4) (x nil) (y gen1) (z gen3))
For a total of 3 facts.
CLIPS>
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3.2 Slot Default Constraints for Pattern-Matching
Single-field slots that are not specified in a pattern on the LHS of a rule are defaulted to
single-field wildcards (?) and multifield slots are defaulted to multifield wildcards ($?).
3.3 Slot Value Constraint Attributes
The syntax and functionality of single and multifield constraint attributes are described in detail
in Section 11. Static and dynamic constraint checking for deftemplates is supported. Static
checking is performed when constructs or commands using deftemplates slots are being parsed
(and the specific deftemplate associated with the construct or command can be immediately
determined). Template patterns used on the LHS of a rule are also checked to determine if
constraint conflicts exist among variables used in more than one slot. Errors for inappropriate
values are immediately signaled. References to fact-indexes made in commands such as modify
and duplicate are considered to be ambiguous and are never checked using static checking.
Static checking is enabled by default. This behavior can be changed using the
set-static-constraint-checking function. Dynamic checking is also supported. If dynamic
checking is enabled, then new deftemplate facts have their values checked when added to the
fact-list. This dynamic checking is disabled by default. This behavior can be changed using the
set-dynamic-constraint-checking function. If a violation occurs when dynamic checking is
being performed, then execution will be halted.
Example
(deftemplate object
(slot name
(type SYMBOL)
(default ?DERIVE))
(slot location
(type SYMBOL)
(default ?DERIVE))
(slot on-top-of
(type SYMBOL)
(default floor))
(slot weight
(allowed-values light heavy)
(default light))
(multislot contents
(type SYMBOL)
(default ?DERIVE)))
3.4 Implied Deftemplates
Asserting or referring to an ordered fact (such as in a LHS pattern) creates an “implied”
deftemplate with a single implied multifield slot. The implied multifield slot’s name is not
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Section 3: Deftemplate Construct
printed when the fact is printed. The implied deftemplate can be manipulated and examined
identically to any user defined deftemplate (although it has no pretty print form).
Example
CLIPS> (clear)
CLIPS> (assert (foo 1 2 3))
<Fact-1>
CLIPS> (defrule yak (bar 4 5 6) =>)
CLIPS> (list-deftemplates)
initial-fact
foo
bar
For a total of 3 deftemplates.
CLIPS> (facts)
f-0 (initial-fact)
f-1 (foo 1 2 3)
For a total of 2 facts.
CLIPS>
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Section 4:
Deffacts Construct
With the deffacts construct, a list of facts can be defined which are automatically asserted
whenever the reset command is performed. Facts asserted through deffacts may be retracted or
pattern-matched like any other fact. The initial fact-list, including any defined deffacts, is always
reconstructed after a reset command.
Syntax
(deffacts <deffacts-name> [<comment>]
<RHS-pattern>*)
Redefining a currently existing deffacts causes the previous deffacts with the same name to be
removed even if the new definition has errors in it. There may be multiple deffacts constructs
and any number of facts (either ordered or deftemplate) may be asserted into the initial fact-list
by each deffacts construct.
Dynamic expressions may be included in a fact by embedding the expression directly within the
fact. All such expressions are evaluated when CLIPS is reset.
Example
(deffacts startup "Refrigerator Status"
(refrigerator light on)
(refrigerator door open)
(refrigerator temp (get-temp)))
Upon startup and after a clear command, CLIPS automatically constructs the following
deftemplate and deffacts.
(deftemplate initial-fact)
(deffacts initial-fact
(initial-fact))
! Important Note
In prior versions of CLIPS, the initial-fact deffacts provided a convenient method for starting the
execution of a system: rules without conditional elements had an (initial-fact) pattern
automatically added to their LHS. When a reset command was issued, the assertion of the
(intial-fact) would activate these rules. Starting with version 6.3 of CLIPS, rules without
conditional elements are automatically matched without the need for the (initial-fact) assertion.
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Section 4: Deffacts Construct
Usage of the initial-fact is now deprecated. Programs should not rely on the assertion of this fact
when a reset is performed.
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Section 5:
Defrule Construct
One of the primary methods of representing knowledge in CLIPS is a rule. A rule is a collection
of conditions and the actions to be taken if the conditions are met. The developer of an expert
system defines the rules that describe how to solve a problem. Rules execute (or fire) based on
the existence or non-existence of facts or instances of user-defined classes. CLIPS provides the
mechanism (the inference engine) which attempts to match the rules to the current state of the
system (as represented by the fact-list and instance-list) and applies the actions.
Throughout this section, the term pattern entity will be used to refer to either a fact or an
instance of a user-defined class.
5.1 Defining Rules
Rules are defined using the defrule construct.
Syntax
(defrule <rule-name> [<comment>]
[<declaration>] ; Rule Properties
<conditional-element>* ; Left-Hand Side (LHS)
=>
<action>*) ; Right-Hand Side (RHS)
Redefining a currently existing defrule causes the previous defrule with the same name to be
removed even if the new definition has errors in it. The LHS is made up of a series of conditional
elements (CEs) that typically consist of pattern conditional elements (or just simply patterns) to
be matched against pattern entities. An implicit and conditional element always surrounds all the
patterns on the LHS. The RHS contains a list of actions to be performed when the LHS of the
rule is satisfied. In addition, the LHS of a rule may also contain declarations about the rule’s
properties immediately following the rule’s name and comment (see section 5.4.10 for more
details). The arrow (=>) separates the LHS from the RHS. There is no limit to the number of
conditional elements or actions a rule may have (other than the limitation placed by actual avail-
able memory). Actions are performed sequentially if, and only if, all conditional elements on the
LHS are satisfied.
If no conditional elements are on the LHS, the rule will automatically be activated. If no actions
are on the RHS, the rule can be activated and fired but nothing will happen.
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As rules are defined, they are incrementally reset. This means that CEs in newly defined rules
can be satisfied by pattern entities at the time the rule is defined, in addition to pattern entities
created after the rule is defined (see sections 13.1.8, 13.6.9, and 13.6.10 for more details).
Example
(defrule example-rule "This is an example of a simple rule"
(refrigerator light on)
(refrigerator door open)
=>
(assert (refrigerator food spoiled)))
5.2 Basic Cycle Of Rule Execution
Once a knowledge base (in the form of rules) is built and the fact-list and instance-list is
prepared, CLIPS is ready to execute rules. In a conventional language the programmer explicitly
defines the starting point, the stopping point, and the sequence of operations. With CLIPS, the
program flow does not need to be defined quite so explicitly. The knowledge (rules) and the data
(facts and instances) are separated, and the inference engine provided by CLIPS is used to apply
the knowledge to the data. The basic execution cycle is as follows:
a) If the rule firing limit has been reached or there is no current focus, then execution is halted.
Otherwise, the top rule on the agenda of the module that is the current focus is selected for
execution. If there are no rules on that agenda, then the current focus is removed from the
focus stack and the current focus becomes the next module on the focus stack. If the focus
stack is empty, then execution is halted, otherwise step a is executed again. See sections
5.4.10.2, 10.6, 12.2, and 13.7 for information on the focus stack and the current focus.
b) The right-hand side (RHS) actions of the selected rule are executed. The use of the return
function on the RHS of a rule may remove the current focus from the focus stack (see
sections 10.6 and 12.6.7). The number of rules fired is incremented for use with the rule
firing limit.
c) As a result of step b, rules may be activated or deactivated. Activated rules (those rules
whose conditions are currently satisfied) are placed on the agenda of the module in which
they are defined. The placement on the agenda is determined by the salience of the rule and
the current conflict resolution strategy (see sections 5.3, 5.4.10, 13.7.5, and 13.7.6).
Deactivated rules are removed from the agenda. If the activations item is being watched (see
section 13.2), then an informational message will be displayed each time a rule is activated
or deactivated.
d) If dynamic salience is being used, the salience values for all rules on the agenda are
reevaluated (see sections 5.4.10, 13.7.9, and 13.7.10). Repeat the cycle beginning with step
a.
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5.3 Conflict Resolution Strategies
The agenda is the list of all rules that have their conditions satisfied (and have not yet been
executed). Each module has its own agenda. The agenda acts similar to a stack (the top rule on
the agenda is the first one to be executed). When a rule is newly activated, its placement on the
agenda is based (in order) on the following factors:
a) Newly activated rules are placed above all rules of lower salience and below all rules of
higher salience.
b) Among rules of equal salience, the current conflict resolution strategy is used to determine
the placement among the other rules of equal salience.
c) If a rule is activated (along with several other rules) by the same assertion or retraction of a
fact, and steps a and b are unable to specify an ordering, then the rule is arbitrarily (not
randomly) ordered in relation to the other rules with which it was activated. Note, in this
respect, the order in which rules are defined has an arbitrary effect on conflict resolution
(which is highly dependent upon the current underlying implementation of rules). Do not
depend upon this arbitrary ordering for the proper execution of your rules.
CLIPS provides seven conflict resolution strategies: depth, breadth, simplicity, complexity, lex,
mea, and random. The default strategy is depth. The current strategy can be set by using the
set-strategy command (which will reorder the agenda based upon the new strategy).
5.3.1 Depth Strategy
Newly activated rules are placed above all rules of the same salience. For example, given that
fact-a activates rule-1 and rule-2 and fact-b activates rule-3 and rule-4, then if fact-a is asserted
before fact-b, rule-3 and rule-4 will be above rule-1 and rule-2 on the agenda. However, the
position of rule-1 relative to rule-2 and rule-3 relative to rule-4 will be arbitrary.
5.3.2 Breadth Strategy
Newly activated rules are placed below all rules of the same salience. For example, given that
fact-a activates rule-1 and rule-2 and fact-b activates rule-3 and rule-4, then if fact-a is asserted
before fact-b, rule-1 and rule-2 will be above rule-3 and rule-4 on the agenda. However, the
position of rule-1 relative to rule-2 and rule-3 relative to rule-4 will be arbitrary.
5.3.3 Simplicity Strategy
Among rules of the same salience, newly activated rules are placed above all activations of rules
with equal or higher specificity. The specificity of a rule is determined by the number of
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comparisons that must be performed on the LHS of the rule. Each comparison to a constant or
previously bound variable adds one to the specificity. Each function call made on the LHS of a
rule as part of the :, =, or test conditional element adds one to the specificity. The boolean
functions and, or, and not do not add to the specificity of a rule, but their arguments do.
Function calls made within a function call do not add to the specificity of a rule. For example,
the following rule
(defrule example
(item ?x ?y ?x)
(test (and (numberp ?x) (> ?x (+ 10 ?y)) (< ?x 100)))
=>)
has a specificity of 5. The comparison to the constant item, the comparison of ?x to its previous
binding, and the calls to the numberp, <, and > functions each add one to the specificity for a
total of 5. The calls to the and and + functions do not add to the specificity of the rule.
5.3.4 Complexity Strategy
Among rules of the same salience, newly activated rules are placed above all activations of rules
with equal or lower specificity.
5.3.5 LEX Strategy
Among rules of the same salience, newly activated rules are placed using the OPS5 strategy of
the same name. First the recency of the pattern entities that activated the rule is used to determine
where to place the activation. Every fact and instance is marked internally with a “time tag” to
indicate its relative recency with respect to every other fact and instance in the system. The
pattern entities associated with each rule activation are sorted in descending order for
determining placement. An activation with a more recent pattern entities is placed before
activations with less recent pattern entities. To determine the placement order of two activations,
compare the sorted time tags of the two activations one by one starting with the largest time tags.
The comparison should continue until one activation’s time tag is greater than the other
activation’s corresponding time tag. The activation with the greater time tag is placed before the
other activation on the agenda.
If one activation has more pattern entities than the other activation and the compared time tags
are all identical, then the activation with more time tags is placed before the other activation on
the agenda. If two activations have the exact same recency, the activation with the higher
specificity is placed above the activation with the lower specificity. Unlike OPS5, the not
conditional elements in CLIPS have pseudo time tags that are used by the LEX conflict
resolution strategy. The time tag of a not CE is always less than the time tag of a pattern entity,
but greater than the time tag of a not CE that was instantiated after the not CE in question.
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As an example, the following six activations have been listed in their LEX ordering (where the
comma at the end of the activation indicates the presence of a not CE). Note that a fact’s time tag
is not necessarily the same as it’s index (since instances are also assigned time tags), but if one
fact’s index is greater than another facts’s index, then it’s time tag is also greater. For this
example, assume that the time tags and indices are the same.
rule-6: f-1,f-4
rule-5: f-1,f-2,f-3,
rule-1: f-1,f-2,f-3
rule-2: f-3,f-1
rule-4: f-1,f-2,
rule-3: f-2,f-1
Shown following are the same activations with the fact indices sorted as they would be by the
LEX strategy for comparison.
rule-6: f-4,f-1
rule-5: f-3,f-2,f-1,
rule-1: f-3,f-2,f-1
rule-2: f-3,f-1
rule-4: f-2,f-1,
rule-3: f-2,f-1
5.3.6 MEA Strategy
Among rules of the same salience, newly activated rules are placed using the OPS5 strategy of
the same name. First the time tag of the pattern entity associated with the first pattern is used to
determine where to place the activation. An activation thats first pattern’s time tag is greater than
another activations first pattern’s time tag is placed before the other activation on the agenda. If
both activations have the same time tag associated with the first pattern, then the LEX strategy is
used to determine placement of the activation. Again, as with the CLIPS LEX strategy, negated
patterns have pseudo time tags.
As an example, the following six activations have been listed in their MEA ordering (where the
comma at the end of the activation indicates the presence of a negated pattern).
rule-2: f-3,f-1
rule-3: f-2,f-1
rule-6: f-1,f-4
rule-5: f-1,f-2,f-3,
rule-1: f-1,f-2,f-3
rule-4: f-1,f-2,
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5.3.7 Random Strategy
Each activation is assigned a random number that is used to determine its placement among
activations of equal salience. This random number is preserved when the strategy is changed so
that the same ordering is reproduced when the random strategy is selected again (among
activations that were on the agenda when the strategy was originally changed).
! Usage Note
A conflict resolution strategy is an implicit mechanism for specifying the order in which rules of
equal salience should be executed. In early expert system tools, this was often the only
mechanism provided to specify the order. Because the mechanism is implicit, it’s not possible to
determine the programmer’s original intent simply by looking at the code. [Of course in the real
world there isn’t a need to guess the original intent because the code is riddled with helpful
comments.] Rather than explicitly indicating that rule A should be executed before rule B, the
order of execution is implicitly determined by the order in which facts are asserted and the
complexity of the rules. The assumption one must make when examining the code is that the
original programmer carefully analyzed the rules and followed the necessary conventions so that
the rules execute in the appropriate sequence.
Because they require explicit declarations, the preferred mechanisms in CLIPS for ordering the
execution of rules are salience and modules. Salience allows one to explicitly specify that one
rule should be executed before another rule. Modules allow one to explicitly specify that all of
the rules in a particular group (module) should be executed before all of the rules in a different
group. Thus, when designing a program the following convention should be followed: if two
rules have the same salience, are in the same module, and are activated concurrently, then the
order in which they are executed should not matter. For example, the following two rules need
correction because they can be activated at the same time, but the order in which they execute
matters:
(defrule rule-1
(factoid a)
=>
(assert (factoid b)))
(defrule rule-2
?f <- (factoid a)
(factoid d)
=>
(retract ?f)
(assert (factoid c)))
Programmers should also be careful to avoid overusing salience. Trying to unravel the
relationships between dozens of salience values can be just as confusing as the implicit use of a
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conflict resolution strategy in determining rule execution order. It’s rarely necessary to use more
than five to ten salience values in a well-designed program.
Most programs should use the default conflict resolution strategy of depth. The breadth,
simplicity, and complexity strategies are provided largely for academic reasons (i.e. the study of
conflict resolution strategies). The lex and mea strategies are provided to help in converting
OPS5 programs to CLIPS.
The random strategy is useful for testing. Because this strategy randomly orders activations
having the same salience, it is useful in detecting whether the execution order of rules with the
same salience effects the program behavior. Before running a program with the random strategy,
first seed the random number generator using the seed function. The same seed value can be
subsequently be used if it is necessary to replicate the results of the program run.
5.4 LHS Syntax
This section describes the syntax used on the LHS of a rule. The LHS of a CLIPS rule is made
up of a series of conditional elements (CEs) that must be satisfied for the rule to be placed on the
agenda. There are eight types of conditional elements: pattern CEs, test CEs, and CEs, or CEs,
not CEs, exists CEs, forall CEs, and logical CEs. The pattern CE is the most basic and
commonly used conditional element. Pattern CEs contain constraints that are used to determine
if any pattern entities (facts or instances) satisfy the pattern. The test CE is used to evaluate
expressions as part of the pattern-matching process. The and CE is used to specify that an entire
group of CEs must all be satisfied. The or CE is used to specify that only one of a group of CEs
must be satisfied. The not CE is used to specify that a CE must not be satisfied. The exists CE is
used to test for the occurence of at least one partial match for a set of CEs. The forall CE is used
to test that a set of CEs is satisfied for every partial match of a specified CE. Finally, the logical
CE allows assertions of facts and the creation of instances on the RHS of a rule to be logically
dependent upon pattern entities matching patterns on the LHS of a rule (truth maintenance).
Syntax
<conditional-element> ::= <pattern-CE> |
<assigned-pattern-CE> |
<not-CE> |
<and-CE> |
<or-CE> |
<logical-CE> |
<test-CE> |
<exists-CE> |
<forall-CE>
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5.4.1 Pattern Conditional Element
Pattern conditional elements consist of a collection of field constraints, wildcards, and
variables which are used to constrain the set of facts or instances which match the pattern CE. A
pattern CE is satisfied by each and every pattern entity that satisfies its constraints. Field
constraints are a set of constraints that are used to test a single field or slot of a pattern entity. A
field constraint may consist of only a single literal constraint, however, it may also consist of
several constraints connected together. In addition to literal constraints, CLIPS provides three
other types of constraints: connective constraints, predicate constraints, and return value
constraints. Wildcards are used within pattern CEs to indicate that a single field or group of
fields can be matched by anything. Variables are used to store the value of a field so that it can
be used later on the LHS of a rule in other conditional elements or on the RHS of a rule as an
argument to an action.
The first field of any pattern must be a symbol and can not use any other constraints. This first
field is used by CLIPS to determine if the pattern applies to an ordered fact, a template fact, or an
instance. The symbol object is reserved to indicate an object pattern. Any other symbol used
must correspond to a deftemplate name (or an implied deftemplate will be created). Slot names
must also be symbols and cannot contain any other constraints.
For object and deftemplate patterns, a single field slot can only contain one field constraint and
that field constraint must only be able to match a single field (no multifield wildcards or
variables). A multifield slot can contain any number of field constraints.
The examples and syntax shown in the following sections will be for ordered and deftemplate
fact patterns. Section 5.4.1.7 will discuss differences between deftemplate patterns and object
patterns. The following constructs are used by the examples.
(deffacts data-facts
(data 1.0 blue "red")
(data 1 blue)
(data 1 blue red)
(data 1 blue RED)
(data 1 blue red 6.9))
(deftemplate person
(slot name)
(slot age)
(multislot friends))
(deffacts people
(person (name Joe) (age 20))
(person (name Bob) (age 20))
(person (name Joe) (age 34))
(person (name Sue) (age 34))
(person (name Sue) (age 20)))
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5.4.1.1 Literal Constraints
The most basic constraint that can be used in a pattern CE is one which precisely defines the
exact value that will match a field. This is called a literal constraint. A literal pattern CE
consists entirely of constants such as floats, integers, symbols, strings, and instance names. It
does not contain any variables or wildcards. All constraints in a literal pattern must be matched
exactly by all fields of a pattern entity.
Syntax
An ordered pattern conditional element containing only literals has the following basic syntax:
(<constant-1> ... <constant-n>)
A deftemplate pattern conditional element containing only literals has the following basic syntax:
(<deftemplate-name> (<slot-name-1> <constant-1>)
•
•
•
(<slot-name-n> <constant-n>))
Example 1
This example utilizes the data-facts deffacts shown in section 5.4.1.
CLIPS> (clear)
CLIPS> (defrule find-data (data 1 blue red) =>)
CLIPS> (reset)
CLIPS> (agenda)
0 find-data: f-3
For a total of 1 activation.
CLIPS> (facts)
f-0 (initial-fact)
f-1 (data 1.0 blue "red")
f-2 (data 1 blue)
f-3 (data 1 blue red)
f-4 (data 1 blue RED)
f-5 (data 1 blue red 6.9)
For a total of 6 facts.
CLIPS>
Example 2
This example utilizes the person deftemplate and people deffacts shown in section 5.4.1.
CLIPS> (clear)
CLIPS>
(defrule Find-Bob
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Section 5: Defrule Construct
(person (name Bob) (age 20))
=>)
CLIPS>
(defrule Find-Sue
(person (age 34) (name Sue))
=>)
CLIPS> (reset)
CLIPS> (agenda)
0 Find-Sue: f-4
0 Find-Bob: f-2
For a total of 2 activations.
CLIPS> (facts)
f-0 (initial-fact)
f-1 (person (name Joe) (age 20) (friends))
f-2 (person (name Bob) (age 20) (friends))
f-3 (person (name Joe) (age 34) (friends))
f-4 (person (name Sue) (age 34) (friends))
f-5 (person (name Sue) (age 20) (friends))
For a total of 6 facts.
CLIPS>
5.4.1.2 Wildcards Single- and Multifield
CLIPS has two wildcard symbols that may be used to match fields in a pattern. CLIPS interprets
these wildcard symbols as standing in place of some part of a pattern entity. The single-field
wildcard, denoted by a question mark character (?), matches any value stored in exactly one
field in the pattern entity. The multifield wildcard, denoted by a dollar sign followed by a
question mark ($?), matches any value in zero or more fields in a pattern entity. Single-field and
multifield wildcards may be combined in a single pattern in any combination. It is illegal to use a
multifield wildcard in a single field slot of a deftemplate or object pattern. By default, an
unspecified single-field slot in a deftemplate/object pattern is matched against an implied
single-field wildcard. Similarly, an unspecified multifield slot in a deftemplate/object pattern is
matched against an implied multifield-wildcard.
Syntax
An ordered pattern conditional element containing only literals and wildcards has the following
basic syntax:
(<constraint-1> ... <constraint-n>)
where
<constraint> ::= <constant> | ? | $?
A deftemplate pattern conditional element containing only literals and wildcards has the
following basic syntax:
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(<deftemplate-name> (<slot-name-1> <constraint-1>)
•
•
•
(<slot-name-n> <constraint-n>))
Example 1
This example utilizes the data-facts deffacts shown in section 5.4.1.
CLIPS> (clear)
CLIPS>
(defrule find-data
(data ? blue red $?)
=>)
CLIPS> (reset)
CLIPS> (agenda)
0 find-data: f-5
0 find-data: f-3
For a total of 2 activations.
CLIPS> (facts)
f-0 (initial-fact)
f-1 (data 1.0 blue "red")
f-2 (data 1 blue)
f-3 (data 1 blue red)
f-4 (data 1 blue RED)
f-5 (data 1 blue red 6.9)
For a total of 6 facts.
CLIPS>
Example 2
This example utilizes the person deftemplate and people deffacts shown in section 5.4.1.
CLIPS> (clear)
CLIPS>
(defrule match-all-persons
(person)
=>)
CLIPS> (reset)
CLIPS> (agenda)
0 match-all-persons: f-5
0 match-all-persons: f-4
0 match-all-persons: f-3
0 match-all-persons: f-2
0 match-all-persons: f-1
For a total of 5 activations.
CLIPS> (facts)
f-0 (initial-fact)
f-1 (person (name Joe) (age 20) (friends))
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f-2 (person (name Bob) (age 20) (friends))
f-3 (person (name Joe) (age 34) (friends))
f-4 (person (name Sue) (age 34) (friends))
f-5 (person (name Sue) (age 20) (friends))
For a total of 6 facts.
CLIPS>
Multifield wildcard and literal constraints can be combined to yield some powerful
pattern-matching capabilities. A pattern to match all of the facts that have the symbol YELLOW
in any field (other than the first) could be written as
(data $? YELLOW $?)
Some examples of what this pattern would match are
(data YELLOW blue red green)
(data YELLOW red)
(data red YELLOW)
(data YELLOW)
(data YELLOW data YELLOW)
The last fact will match twice since YELLOW appears twice in the fact. The use of multifield
wildcards should be confined to cases of patterns in which the single-field wildcard cannot create
a pattern that satisfies the match required, since the multifield wildcard produces every possible
match combination that can be derived from a pattern entity. This derivation of matches requires
a significant amount of time to perform when compared to the time needed to perform a
single-field match.
5.4.1.3 Variables Single- and Multifield
Wildcard symbols replace portions of a pattern and accept any value. The value of the field being
replaced may be captured in a variable for comparison, display, or other manipulations. This is
done by directly following the wildcard symbol with a variable name.
Syntax
Expanding on the syntax definition given in section 5.4.1.2 now gives:
<constraint> ::= <constant> | ? | $? |
<single-field-variable> |
<multifield-variable>
<single-field-variable> ::= ?<variable-symbol>
<multifield-variable> ::= $?<variable-symbol>
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where <variable-symbol> is similar to a symbol, except that it must start with an alphabetic char-
acter. Double quotes are not allowed as part of a variable name; i.e. a string cannot be used for a
variable name. The rules for pattern-matching are similar to those for wildcard symbols. On its
first appearance, a variable acts just like a wildcard in that it will bind to any value in the field(s).
However, later appearances of the variable require the field(s) to match the binding of the
variable. The binding will only be true within the scope of the rule in which it occurs. Each rule
has a private list of variable names with their associated values; thus, variables are local to a rule.
Bound variables can be passed to external functions. The $ operator has special significance on
the LHS as a pattern-matching operator to indicate that zero or more fields need to be matched.
In other places (such as the RHS of a rule), the $ in front of a variable indicates that sequence
expansion should take place before calling the function. Thus, when passed as parameters in
function calls (either on the LHS or RHS of a rule), multifield variables should not be preceded
by the $ (unless sequence expansion is desired). All other uses of a multifield variable on the
LHS of a rule, however, should use the $. It is illegal to use a multifield variable in a single field
slot of a deftemplate/object pattern.
Example 1
CLIPS> (clear)
CLIPS> (reset)
CLIPS> (assert (data 2 blue green)
(data 1 blue)
(data 1 blue red))
<Fact-3>
CLIPS> (facts)
f-0 (initial-fact)
f-1 (data 2 blue green)
f-2 (data 1 blue)
f-3 (data 1 blue red)
For a total of 4 facts.
CLIPS>
(defrule find-data-1
(data ?x ?y ?z)
=>
(printout t ?x " : " ?y " : " ?z crlf))
CLIPS> (run)
1 : blue : red
2 : blue : green
CLIPS>
Example 2
CLIPS> (reset)
CLIPS> (assert (data 1 blue)
(data 1 blue red)
(data 1 blue red 6.9))
<Fact-3>
CLIPS> (facts)
f-0 (initial-fact)
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f-1 (data 1 blue)
f-2 (data 1 blue red)
f-3 (data 1 blue red 6.9)
For a total of 4 facts.
CLIPS>
(defrule find-data-1
(data ?x $?y ?z)
=>
(printout t "?x = " ?x crlf
"?y = " ?y crlf
"?z = " ?z crlf
"------" crlf))
CLIPS> (run)
?x = 1
?y = (blue red)
?z = 6.9
------
?x = 1
?y = (blue)
?z = red
------
?x = 1
?y = ()
?z = blue
------
CLIPS>
Once the initial binding of a variable occurs, all references to that variable have to match the
value that the first binding matched. This applies to both single- and multifield variables. It also
applies across patterns.
Example 3
CLIPS> (clear)
CLIPS>
(deffacts data
(data red green)
(data purple blue)
(data purple green)
(data red blue green)
(data purple blue green)
(data purple blue brown))
CLIPS>
(defrule find-data-1
(data red ?x)
(data purple ?x)
=>)
CLIPS>
(defrule find-data-2
(data red $?x)
(data purple $?x)
=>)
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CLIPS> (reset)
CLIPS> (facts)
f-0 (initial-fact)
f-1 (data red green)
f-2 (data purple blue)
f-3 (data purple green)
f-4 (data red blue green)
f-5 (data purple blue green)
f-6 (data purple blue brown)
For a total of 7 facts.
CLIPS> (agenda)
0 find-data-2: f-4,f-5
0 find-data-1: f-1,f-3
0 find-data-2: f-1,f-3
For a total of 3 activations.
CLIPS>
5.4.1.4 Connective Constraints
Three connective constraints are available for connecting individual constraints and variables to
each other. These are the & (and), | (or), and ~ (not) connective constraints. The & constraint is
satisfied if the two adjoining constraints are satisfied. The | constraint is satisfied if either of the
two adjoining constraints is satisfied. The ~ constraint is satisfied if the following constraint is
not satisfied. The connective constraints can be combined in almost any manner or number to
constrain the value of specific fields while pattern-matching. The ~ constraint has highest
precedence, followed by the & constraint, followed by the | constraint. Otherwise, evaluation of
multiple constraints can be considered to occur from left to right. There is one exception to the
precedence rules that applies to the binding occurrence of a variable. If the first constraint is a
variable followed by an & connective constraint, then the first constraint is treated as a separate
constraint which also must be satisified. Thus the constraint ?x&red|blue is treated like
?x&(red|blue) rather than (?x&red)|blue as the normal precedence rules would indicate.
Basic Syntax
Connective constraints have the following basic syntax:
<term-1>&<term-2> ... &<term-3>
<term-1>|<term-2> ... |<term-3>
~<term>
where <term> could be a single-field variable, multifield variable, constant, or connected
constraint.
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Syntax
Expanding on the syntax definition given in section 5.4.1.3 now gives:
<constraint> ::= ? | $? | <connected-constraint>
<connected-constraint>
::= <single-constraint> |
<single-constraint> & <connected-constraint> |
<single-constraint> | <connected-constraint>
<single-constraint> ::= <term> | ~<term>
<term> ::= <constant> |
<single-field-variable> |
<multifield-variable>
The & constraint typically is used only in conjunction with other constraints or variable bindings.
Notice that connective constraints may be used together and/or with variable bindings. If the first
term of a connective constraint is the first occurrence of a variable name, then the field will be
constrained only by the remaining field constraints. The variable will be bound to the value of
the field. If the variable has been bound previously, it is considered an additional constraint
along with the remaining field constraints; i.e., the field must have the same value already bound
to the variable and must satisfy the field constraints.
Example 1
CLIPS> (clear)
CLIPS> (deftemplate data-B (slot value))
CLIPS>
(deffacts AB
(data-A green)
(data-A blue)
(data-B (value red))
(data-B (value blue)))
CLIPS>
(defrule example1-1
(data-A ~blue)
=>)
CLIPS>
(defrule example1-2
(data-B (value ~red&~green))
=>)
CLIPS>
(defrule example1-3
(data-B (value green|red))
=>)
CLIPS> (reset)
CLIPS> (facts)
f-0 (initial-fact)
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f-1 (data-A green)
f-2 (data-A blue)
f-3 (data-B (value red))
f-4 (data-B (value blue))
For a total of 5 facts.
CLIPS> (agenda)
0 example1-2: f-4
0 example1-3: f-3
0 example1-1: f-1
For a total of 3 activations.
CLIPS>
Example 2
CLIPS> (clear)
CLIPS> (deftemplate data-B (slot value))
CLIPS>
(deffacts B
(data-B (value red))
(data-B (value blue)))
CLIPS>
(defrule example2-1
(data-B (value ?x&~red&~green))
=>
(printout t "?x in example2-1 = " ?x crlf))
CLIPS>
(defrule example2-2
(data-B (value ?x&green|red))
=>
(printout t "?x in example2-2 = " ?x crlf))
CLIPS> (reset)
CLIPS> (run)
?x in example2-1 = blue
?x in example2-2 = red
CLIPS>
Example 3
CLIPS> (clear)
CLIPS> (deftemplate data-B (slot value))
CLIPS>
(deffacts AB
(data-A green)
(data-A blue)
(data-B (value red))
(data-B (value blue)))
CLIPS>
(defrule example3-1
(data-A ?x&~green)
(data-B (value ?y&~?x))
=>)
CLIPS>
(defrule example3-2
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(data-A ?x)
(data-B (value ?x&green|blue))
=>)
CLIPS>
(defrule example3-3
(data-A ?x)
(data-B (value ?y&blue|?x))
=>)
CLIPS> (reset)
CLIPS> (facts)
f-0 (initial-fact)
f-1 (data-A green)
f-2 (data-A blue)
f-3 (data-B (value red))
f-4 (data-B (value blue))
For a total of 5 facts.
CLIPS> (agenda)
0 example3-3: f-1,f-4
0 example3-3: f-2,f-4
0 example3-2: f-2,f-4
0 example3-1: f-2,f-3
For a total of 4 activations.
CLIPS>
5.4.1.5 Predicate Constraints
Sometimes it becomes necessary to constrain a field based upon the truth of a given boolean
expression. CLIPS allows the use of a predicate constraint to restrict a field in this manner. The
predicate constraint allows a predicate function (one returning the symbol FALSE for
unsatisfied and a non-FALSE value for satisfied) to be called during the pattern-matching
process. If the predicate function returns a non-FALSE value, the constraint is satisfied. If the
predicate function returns the symbol FALSE, the constraint is not satisfied. A predicate
constraint is invoked by following a colon with an appropriate function call to a predicate
function. Typically, predicate constraints are used in conjunction with a connective constraint
and a variable binding (i.e. you have to bind the variable to be tested and then connect it to the
predicate constraint).
Basic Syntax
:<function-call>
Syntax
Expanding on the syntax definition given in section 5.4.1.4 now gives:
<term> ::= <constant> |
<single-field-variable> |
<multifield-variable> |
:<function-call>
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Multiple predicate constraints may be used to constrain a single field. CLIPS provides several
predicate functions (see section 12.2). Users also may develop their own predicate functions.
Example 1
CLIPS> (clear)
CLIPS>
(defrule example-1
(data ?x&:(numberp ?x))
=>)
CLIPS> (assert (data 1) (data 2) (data red))
<Fact-3>
CLIPS> (agenda)
0 example-1: f-2
0 example-1: f-1
For a total of 2 activations.
CLIPS>
Example 2
CLIPS> (clear)
CLIPS>
(defrule example-2
(data ?x&~:(symbolp ?x))
=>)
CLIPS> (assert (data 1) (data 2) (data red))
<Fact-3>
CLIPS> (agenda)
0 example-2: f-2
0 example-2: f-1
For a total of 2 activations.
CLIPS>
Example 3
CLIPS> (clear)
CLIPS>
(defrule example-3
(data ?x&:(numberp ?x)&:(oddp ?x))
=>)
CLIPS> (assert (data 1) (data 2) (data red))
<Fact-3>
CLIPS> (agenda)
0 example-3: f-1
For a total of 1 activation.
CLIPS>
Example 4
CLIPS> (clear)
CLIPS>
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Section 5: Defrule Construct
(defrule example-4
(data ?y)
(data ?x&:(> ?x ?y))
=>)
CLIPS> (assert (data 3) ; f-1
(data 5) ; f-2
(data 9)) ; f-3
<Fact-3>
CLIPS> (agenda)
0 example-4: f-1,f-3
0 example-4: f-2,f-3
0 example-4: f-1,f-2
For a total of 3 activations.
CLIPS>
Example 5
CLIPS> (clear)
CLIPS>
(defrule example-5
(data $?x&:(> (length$ ?x) 2))
=>)
CLIPS> (assert (data 1) ; f-1
(data 1 2) ; f-2
(data 1 2 3)) ; f-3
<Fact-3>
CLIPS> (agenda)
0 example-5: f-3
For a total of 1 activation.
CLIPS>
5.4.1.6 Return Value Constraints
It is possible to use the return value of an external function to constrain the value of a field. The
return value constraint (=) allows the user to call external functions from inside a pattern. (This
constraint is different from the comparison function that uses the same symbol. The difference
can be determined from context.) The return value must be one of the primitive data types. This
value is incorporated directly into the pattern at the position at which the function was called as
if it were a literal constraint, and any matching patterns must match this value as though the rule
were typed with that value. Note that the function is evaluated each time the constraint is
checked (not just once).
Basic Syntax
=<function-call>
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Syntax
Expanding on the syntax definition given in section 5.4.1.5 now gives:
<term> ::= <constant> |
<single-field-variable> |
<multifield-variable> |
:<function-call> |
=<function-call>
Example 1
CLIPS> (clear)
CLIPS> (deftemplate data (slot x) (slot y))
CLIPS>
(defrule twice
(data (x ?x) (y =(* 2 ?x)))
=>)
CLIPS> (assert (data (x 2) (y 4)) ; f-1
(data (x 3) (y 9))) ; f-2
<Fact-1>
CLIPS> (agenda)
0 twice: f-1
For a total of 1 activation.
CLIPS>
Example 2
CLIPS> (clear)
CLIPS>
(defclass DATA (is-a USER)
(slot x))
CLIPS>
(defrule return-value-example-2
(object (is-a DATA)
(x ?x1))
(object (is-a DATA)
(x ?x2&=(+ 5 ?x1)|=(- 12 ?x1)))
=>)
CLIPS> (make-instance of DATA (x 4))
[gen1]
CLIPS> (make-instance of DATA (x 9))
[gen2]
CLIPS> (make-instance of DATA (x 3))
[gen3]
CLIPS> (agenda)
0 return-value-example-2: [gen3],[gen2]
0 return-value-example-2: [gen2],[gen3]
0 return-value-example-2: [gen1],[gen2]
For a total of 3 activations.
CLIPS>
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5.4.1.7 Pattern-Matching with Object Patterns
Instances of user-defined classes in COOL can be pattern-matched on the left-hand side of rules.
Patterns can only match objects for which the object’s most specific class is defined before the
pattern and which are in scope for the current module. Any classes that could have objects that
match the pattern cannot be deleted or changed until the pattern is deleted. Even if a rule is
deleted by its RHS, the classes bound to its patterns cannot be changed until after the RHS
finishes executing.
When an instance is created or deleted, all patterns applicable to that object are updated.
However, when a slot is changed, only those patterns that explicitly match on that slot are
affected. Thus, one could use logical dependencies to hook to a change to a particular slot (rather
than a change to any slot, which is all that is possible with deftemplates).
Changes to non-reactive slots or instances of non-reactive classes (see sections 9.3.2.2 and
9.3.3.7) will have no effect on rules. Also Rete network activity will not be immediately apparent
after changes to slots are made if pattern-matching is being delayed through the use of the
make-instance, initialize-instance, modify-instance, message-modify-instance,
duplicate-instance, message-duplicate-instance or object-pattern-match-delay functions.
Syntax
<object-pattern> ::= (object <attribute-constraint>*)
<attribute-constraint> ::= (is-a <constraint>) |
(name <constraint>) |
(<slot-name> <constraint>*)
The is-a constraint is used for specifying class constraints such as “Is this object a member of
class FOO?”. The is-a constraint also encompasses subclasses of the matching classes unless
specifically excluded by the pattern. The name constraint is used for specifying a specific
instance on which to pattern-match. The evaluation of the name constraint must be of primitive
type instance-name, not symbol. Multifield constraints (such as $?) cannot be used with the is-a
or name constraints. Other than these special cases, constraints used in object slots work
similarly to constraints used in deftemplate slots. As with deftemplate patterns, slot names for
object patterns must be symbols and can not contain any other constraints.
Example 1
The following rules illustrate pattern-matching on an object's class.
(defrule class-match-1
(object)
=>)
(defrule class-match-2
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(object (is-a FOO))
=>)
(defrule class-match-3
(object (is-a FOO | BAR))
=>)
(defrule class-match-4
(object (is-a ?x))
(object (is-a ~?x))
=>)
Rule class-match-1 is satisified by all instances of any reactive class. Rule class-match-2 is
satisfied by all instances of class FOO. Rule class-match-3 is satisfied by all instances of class
FOO or BAR. Rule class-match-4 will be satisfied by any two instances of mutually exclusive
classes.
Example 2
The following rules illustrate pattern-matching on various attributes of an object's slots.
(defrule slot-match-1
(object (width))
=>)
(defrule slot-match-2
(object (width ?))
=>)
(defrule slot-match-3
(object (width $?))
=>)
Rule slot-match-1 is satisfied by all instances of reactive classes that contain a reactive width slot
with a zero length multifield value. Rule slot-match-2 is satisfied by all instances of reactive
classes that contain a reactive single or multifield width slot that is bound to a single value. Rule
slot-match-3 is satisfied by all instances of reactive classes that contain a reactive single or
multifield width slot that is bound to any number of values. Note that a slot containing a zero
length multifield value would satisfy rules slot-match-1 and slot-match-3, but not rule
slot-match-2 (because the value's cardinality is zero).
Example 3
The following rules illustrate pattern-matching on the slot values of an object.
(defrule value-match-1
(object (width 10)
=>)
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(defrule value-match-2
(object (width ?x&:(> ?x 20)))
=>)
(defrule value-match-3
(object (width ?x) (height ?x))
=>)
Rule value-match-1 is satisified by all instances of reactive classes that contain a reactive width
slot with value 10. Rule value-match-2 is satisfied by all instances of reactive classes that contain
a reactive width slot that has a value greater than 20. Rule value-match-3 is satisfied by all
instances of reactive classes that contain a reactive width and height slots with the same value.
5.4.1.8 Pattern-Addresses
Certain RHS actions, such as retract and unmake-instance, operate on an entire pattern CE. To
signify which fact or instance they are to act upon, a variable can be bound to the fact-address
or instance-address of a pattern CE. Collectively, fact-addresses and instance-addresses bound
on the LHS of a rule are referred to as pattern-addresses.
Syntax
<assigned-pattern-CE> ::= ?<variable-symbol> <- <pattern-CE>
The left arrow, <-, is a required part of the syntax. A variable bound to a fact-address or
instance-address can be compared to other variables or passed to external functions. Variables
bound to a fact or instance-address may later be used to constrain fields within a pattern CE,
however, the reverse is not allowed. It is an error to bind a varible to a not CE.
Examples
(defrule dummy
(data 1)
?fact <- (dummy pattern)
=>
(retract ?fact))
(defrule compare-facts-1
?f1 <- (color ~red)
?f2 <- (color ~green)
(test (neq ?f1 ?f2))
=>
(printout t "Rule fires from different facts" crlf))
(defrule compare-facts-2
?f1 <- (color ~red)
?f2 <- (color ~green&:(neq ?f1 ?f2))
=>
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(printout t "Rule fires from different facts" crlf))
(defrule print-and-delete-all-objects
?ins <- (object)
=>
(send ?ins print)
(unmake-instance ?ins))
5.4.2 Test Conditional Element
Field constraints used within pattern CEs allow very descriptive constraints to be applied to
pattern-matching. Additional capability is provided with the test conditional element. The test
CE is satisfied if the function call within the test CE evaluates to a non-FALSE value and
unsatisfied if the function call evaluates to FALSE. As with predicate constraints, the user can
compare the variable bindings that already have occurred in any manner. Mathematical
comparisons on variables (e.g., is the difference between ?x and ?y greater than some value?)
and complex logical or equality comparisons can be done. External functions also can be called
which compare variables in any way that the user desires.
Any kind of external function may be embedded within a test conditional element (or within
field constraints). User-defined predicate functions must take arguments as defined in the
Advanced Programming Guide. CLIPS provides several predicate functions (see section 12.1).
Syntax
<test-CE> ::= (test <function-call>)
Since the symbol test is used to indicate this type of conditional element, rules may not use the
symbol test as the first field in a pattern CE. A test CE is evaluated when all proceeding CEs are
satisfied. This means that a test CE will be evaluated more than once if the proceeding CEs can
be satisfied by more than one group of pattern entities. In order to cause the reevaluation of a test
CE, a pattern entity matching a CE prior to the test CE must be changed.
Example 1
This example checks to see if the difference between two numbers is greater than or equal to
three:
CLIPS> (clear)
CLIPS>
(defrule example-1
(data ?x)
(value ?y)
(test (>= (abs (- ?y ?x)) 3))
=>)
CLIPS> (assert (data 6) (value 9))
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<Fact-2>
CLIPS> (agenda)
0 example-1: f-1,f-2
For a total of 1 activation.
CLIPS>
Example 2
This example checks to see if there is a positive slope between two points on a line.
CLIPS> (clear)
CLIPS>
(deffunction positive-slope
(?x1 ?y1 ?x2 ?y2)
(< 0 (/ (- ?y2 ?y1) (- ?x2 ?x1))))
CLIPS>
(defrule example-2
(point ?a ?x1 ?y1)
(point ?b ?x2 ?y2)
(test (> ?b ?a))
(test (positive-slope ?x1 ?y1 ?x2 ?y2))
=>)
CLIPS>
(assert (point 1 4.0 7.0) (point 2 5.0 9.0))
<Fact-2>
CLIPS> (agenda)
0 example-2: f-1,f-2
For a total of 1 activation.
CLIPS>
5.4.3 Or Conditional Element
The or conditional element allows any one of several conditional elements to activate a rule. If
any of the conditional elements inside of the or CE is satisfied, then the or CE is satisfied. If all
other LHS conditional elements are satisfied, the rule will be activated. Note that a rule will be
activated for each conditional element with an or CE that is satisfied (assuming the other
conditional elements of the rule are also satisfied). Any number of conditional elements may
appear within an or CE. The or CE produces the identical effect of writing several rules with
similar LHS’s and RHS’s.
Syntax
<or-CE> ::= (or <conditional-element>+)
Again, if more than one of the conditional elements in the or CE can be met, the rule will fire
multiple times, once for each satisfied combination of conditions.
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Example
(defrule system-fault
(error-status unknown)
(or (temp high)
(valve broken)
(pump (status off)))
=>
(printout t "The system has a fault." crlf))
Note that the above example is exactly equivalent to the following three (separate) rules:
(defrule system-fault
(error-status unknown)
(pump (status off))
=>
(printout t "The system has a fault." crlf))
(defrule system-fault
(error-status unknown)
(valve broken)
=>
(printout t "The system has a fault." crlf))
(defrule system-fault
(error-status unknown)
(temp high)
=>
(printout t "The system has a fault." crlf))
5.4.4 And Conditional Element
CLIPS assumes that all rules have an implicit and conditional element surrounding the
conditional elements on the LHS. This means that all conditional elements on the LHS must be
satisfied before the rule can be activated. An explicit and conditional element is provided to
allow the mixing of and CEs and or CEs. This allows other types of conditional elements to be
grouped together within or and not CEs. The and CE is satisfied if all of the CEs inside of the
explicit and CE are satisfied. If all other LHS conditions are true, the rule will be activated. Any
number of conditional elements may be placed within an and CE. Note that the LHS of any rule
is enclosed within an implied and CE.
Syntax
<and-CE> ::= (and <conditional-element>+)
Example
(defrule system-flow
(error-status confirmed)
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(or (and (temp high)
(valve closed))
(and (temp low)
(valve open)))
=>
(printout t "The system is having a flow problem." crlf))
5.4.5 Not Conditional Element
Sometimes the lack of information is meaningful; i.e., one wishes to fire a rule if a pattern entity
or other CE does not exist. The not conditional element provides this capability. The not CE is
satisfied only if the conditional element contained within it is not satisfied. As with other
conditional elements, any number of additional CEs may be on the LHS of the rule and field con-
straints may be used within the negated pattern.
Syntax
<not-CE> ::= (not <conditional-element>)
Only one CE may be negated at a time. Multiple patterns may be negated by using multiple not
CEs. Care must be taken when combining not CEs with or and and CEs; the results are not
always obvious! The same holds true for variable bindings within a not CE. Previously bound
variables may be used freely inside of a not CE. However, variables bound for the first time
within a not CE can be used only in that pattern.
Examples
(defrule high-flow-rate
(temp high)
(valve open)
(not (error-status confirmed))
=>
(printout t "Recommend closing of valve due to high temp"
crlf))
(defrule check-valve
(check-status ?valve)
(not (valve-broken ?valve))
=>
(printout t "Device " ?valve " is OK" crlf))
(defrule double-pattern
(data red)
(not (data red ?x ?x))
=>
(printout t "No patterns with red green green!" crlf ))
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5.4.6 Exists Conditional Element
The exists conditional element provides a mechanism for determining if a group of specified
CEs is satisfied by a least one set of pattern entities.
Syntax
<exists-CE> ::= (exists <conditional-element>+)
The exists CE is implemented by replacing the exists keyword with two nested not CEs. For
example, the following rule
(defrule example
(exists (a ?x) (b ?x))
=>)
is equivalent to the rule below
(defrule example
(not (not (and (a ?x) (b ?x))))
=>)
Because of the way the exists CE is implemented using not CEs, the restrictions which apply to
CEs found within not CEs (such as binding a pattern CE to a fact-address) also apply to the CEs
found within an exists CE.
Example
Given the following constructs,
CLIPS> (clear)
CLIPS>
(deftemplate hero
(multislot name)
(slot status (default unoccupied)))
CLIPS>
(deffacts goal-and-heroes
(goal save-the-day)
(hero (name Death Defying Man))
(hero (name Stupendous Man))
(hero (name Incredible Man)))
CLIPS>
(defrule save-the-day
(goal save-the-day)
(exists (hero (status unoccupied)))
=>
(printout t "The day is saved." crlf))
CLIPS>
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the following commands illustrate that even though there are three facts which can match the
second CE in the save-the-day rule, there is only one partial match generated.
CLIPS> (reset)
CLIPS> (agenda)
0 save-the-day: f-1,*
For a total of 1 activation.
CLIPS> (facts)
f-0 (initial-fact)
f-1 (goal save-the-day)
f-2 (hero (name Death Defying Man) (status unoccupied))
f-3 (hero (name Stupendous Man) (status unoccupied))
f-4 (hero (name Incredible Man) (status unoccupied))
For a total of 5 facts.
CLIPS> (matches save-the-day)
Matches for Pattern 1
f-1
Matches for Pattern 2
f-2
f-3
f-4
Partial matches for CEs 1 - 2
f-1,*
Activations
f-1,*
(4 1 1)
CLIPS>
5.4.7 Forall Conditional Element
The forall conditional element provides a mechanism for determining if a group of specified
CEs is satisfied for every occurence of another specified CE.
Syntax
<forall-CE> ::= (forall <conditional-element>
<conditional-element>+)
The forall CE is implemented by replacing the forall keyword with combinations of not and
and CEs. For example, the following rule
(defrule example
(forall (a ?x) (b ?x) (c ?x))
=>)
is equivalent to the rule below
(defrule example
(not (and (a ?x)
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(not (and (b ?x) (c ?x)))))
=>)
Because of the way the forall CE is implemented using not CEs, the restrictions which apply to
CE found within not CEs (such as binding a pattern CE to a fact-address) also apply to the CEs
found within an forall CE.
Example
The following rule determines if every student has passed in reading, writing, and arithmetic by
using the forall CE.
CLIPS> (clear)
CLIPS>
(defrule all-students-passed
(forall (student ?name)
(reading ?name)
(writing ?name)
(arithmetic ?name))
=>
(printout t "All students passed." crlf))
CLIPS>
The following commands illustrate how the forall CE works in the all-students-passed rule. Note
that initially the all-students-passed rule is satisfied because there are no students.
CLIPS> (reset)
CLIPS> (agenda)
0 all-students-passed: *
For a total of 1 activation.
CLIPS>
After the (student Bob) fact is asserted, the rule is no longer satisfied since Bob has not passed
reading, writing, and arithmetic.
CLIPS> (assert (student Bob))
<Fact-1>
CLIPS> (agenda)
CLIPS>
The rule is still not satisfied after Bob has passed reading and writing, since he still has not
passed arithmetic.
CLIPS> (assert (reading Bob) (writing Bob))
<Fact-3>
CLIPS> (agenda)
CLIPS>
Once Bob has passed arithmetic, the all-students-passed rule is reactivated.
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CLIPS> (assert (arithmetic Bob))
<Fact-4>
CLIPS> (agenda)
0 all-students-passed: *
For a total of 1 activation.
CLIPS>
If a new student is asserted, then the rule is taken off the agenda, since John has not passed
reading, writing, and arithmetic.
CLIPS> (assert (student John))
<Fact-5>
CLIPS> (agenda)
CLIPS>
Removing both student facts reactivates the rule again.
CLIPS> (retract 1 5)
CLIPS> (agenda)
0 all-students-passed: *
For a total of 1 activation.
CLIPS>
5.4.8 Logical Conditional Element
The logical conditional element provides a truth maintenance capability for pattern entities
(facts or instances) created by rules that use the logical CE. A pattern entity created on the RHS
(or as a result of actions performed from the RHS) can be made logically dependent upon the
pattern entities that matched the patterns enclosed with the logical CE on the LHS of the rule.
The pattern entities matching the LHS logical patterns provide logical support to the facts and
instance created by the RHS of the rule. A pattern entity can be logically supported by more than
one group of pattern entities from the same or different rules. If any one supporting pattern
entities is removed from a group of supporting pattern entities (and there are no other supporting
groups), then the pattern entity is removed.
If a pattern entity is created without logical support (e.g., from a deffacts, definstaces, as a
top-level command, or from a rule without any logical patterns), then the pattern entity has
unconditional support. Unconditionally supporting a pattern entity removes all logical support
(without causing the removal of the pattern entity). In addition, further logical support for an
unconditionally supported pattern entity is ignored. Removing a rule that generated logical
support for a pattern entity, removes the logical support generated by that rule (but does not
cause the removal of the pattern entity if no logical support remains).
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Syntax
<logical-CE> ::= (logical <conditional-element>+)
The logical CE groups patterns together exactly as the explicit and CE does. It may be used in
conjunction with the and, or, and not CEs. However, only the first N patterns of a rule can have
the logical CE applied to them. For example, the following rule is legal
(defrule ok
(logical (a))
(logical (b))
(c)
=>
(assert (d)))
whereas the following rules are illegal
(defrule not-ok-1
(logical (a))
(b)
(logical (c))
=>
(assert (d)))
(defrule not-ok-2
(a)
(logical (b))
(logical (c))
=>
(assert (d)))
(defrule not-ok-3
(or (a)
(logical (b)))
(logical (c))
=>
(assert (d)))
Example
Given the following rules,
CLIPS> (clear)
CLIPS>
(defrule rule1
(logical (a))
(logical (b))
(c)
=>
(assert (g) (h)))
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CLIPS>
(defrule rule2
(logical (d))
(logical (e))
(f)
=>
(assert (g) (h)))
CLIPS>
the following commands illustrate how logical dependencies work.
CLIPS> (watch facts)
CLIPS> (watch activations)
CLIPS. (watch rules)
CLIPS> (assert (a) (b) (c) (d) (e) (f))
==> f-1 (a)
==> f-2 (b)
==> f-3 (c)
==> Activation 0 rule1: f-1,f-2,f-3
==> f-4 (d)
==> f-5 (e)
==> f-6 (f)
==> Activation 0 rule2: f-4,f-5,f-6
<Fact-6>
CLIPS> (run)
FIRE 1 rule2: f-4,f-5,f-6 ; 1st rule adds logical support
==> f-7 (g)
==> f-8 (h)
FIRE 2 rule1: f-1,f-2,f-3 ; 2nd rule adds further support
CLIPS> (retract 1)
<== f-1 (a) ; Removes 1st support for (g) and (h)
CLIPS> (assert (h)) ; (h) is unconditionally supported
FALSE
CLIPS> (retract 4)
<== f-4 (d) ; Removes 2nd support for (g)
<== f-7 (g) ; (g) has no more support
CLIPS> (unwatch all)
CLIPS>
As mentioned in section 5.4.1.7, the logical CE can be used with an object pattern to create
pattern entities that are logically dependent on changes to specific slots in the matching
instance(s) rather than all slots. This cannot be accomplished with template facts because a
change to a template fact slot actually involves the retraction of the old template fact and the
assertion of a new one, whereas a change to an instance slot is done in place. The example below
illustrates this behavior:
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot foo)
(slot bar))
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CLIPS>
(deftemplate A
(slot foo)
(slot bar))
CLIPS>
(defrule match-A-s
(logical (object (is-a A) (foo ?))
(A (foo ?)))
=>
(assert (new-fact)))
CLIPS> (make-instance a of A)
[a]
CLIPS> (assert (A))
<Fact-1>
CLIPS> (watch facts)
CLIPS> (run)
==> f-2 (new-fact)
CLIPS> (send [a] put-bar 100)
100
CLIPS> (agenda)
CLIPS> (modify 1 (bar 100))
<== f-1 (A (foo nil) (bar nil))
<== f-2 (new-fact)
==> f-3 (A (foo nil) (bar 100))
<Fact-3>
CLIPS> (agenda)
0 match-A-s: [a],f-3
For a total of 1 activation.
CLIPS> (run)
==> f-4 (new-fact)
CLIPS> (send [a] put-foo 100)
<== f-4 (new-fact)
100
CLIPS> (agenda)
0 match-A-s: [a],f-3
For a total of 1 activation.
CLIPS> (unwatch facts)
CLIPS>
5.4.9 Automatic Replacement of LHS CEs
Under certain circumstances, CLIPS will change the CEs specified in the rule LHS.
5.4.9.1 Or CEs Following Not CEs
If an or CE immediately follows a not CE, then the not/or CE combination is replaced with an
and/not CE combination where each of the CEs contained in the original or CE is enclosed
within a not CE and then all of the not CEs are enclosed within a single and CE. For example,
the following rule
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(defrule example
(a ?x)
(not (or (b ?x)
(c ?x)))
=>)
would be changed as follows.
(defrule example
(a ?x)
(and (not (b ?x))
(not (c ?x)))
=>)
5.4.10 Declaring Rule Properties
This feature allows the properties or characteristics of a rule to be defined. The characteristics are
declared on the LHS of a rule using the declare keyword. A rule may only have one declare
statement and it must appear before the first conditional element on the LHS (as shown in section
5.1).
Syntax
<declaration> ::= (declare <rule-property>+)
<rule-property> ::= (salience <integer-expression>) |
(auto-focus <boolean-symbol>)
<boolean-symbol> ::= TRUE | FALSE
5.4.10.1 The Salience Rule Property
The salience rule property allows the user to assign a priority to a rule. When multiple rules are
in the agenda, the rule with the highest priority will fire first. The declared salience value should
be an expression that evaluates to an an integer in the range -10000 to +10000. Salience
expressions may freely reference global variables and other functions (however, you should
avoid using functions with side-effects). If unspecified, the salience value for a rule defaults to
zero.
Example
(defrule test-1
(declare (salience 99))
(fire test-1)
=>
(printout t "Rule test-1 firing." crlf))
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(defrule test-2
(declare (salience (+ ?*constraint-salience* 10)))
(fire test-2)
=>
(printout t "Rule test-2 firing." crlf))
Salience values can be evaluated at one of three times: when a rule is defined, when a rule is
activated, and every cycle of execution (the latter two situations are referred to as dynamic
salience). By default, salience values are only evaluated when a rule is defined. The
set-salience-evaluation command can be used to change this behavior. Note that each salience
evaluation method encompasses the previous method (i.e. if saliences are evaluated every cycle,
then they are also evaluated when rules are activated or defined).
! Usage Note
Despite the large number of possible values, with good design there’s rarely a need for more than
five salience values in a simple program and ten salience values in a complex program. Defining
the salience values as global variables allows you to specify and document the values used by
your program in a centralized location and also makes it easier to change the salience of a group
of rules sharing the same salience value:
(defglobal ?*high-priority* = 100)
(defglobal ?*low-priority* = -100)
(defrule rule-1
(declare (salience ?*high-priority*))
=>)
(defrule rule-2
(declare (salience ?*low-priority*))
=>)
5.4.10.2 The Auto-Focus Rule Property
The auto-focus rule property allows an automatic focus command to be executed whenever a
rule becomes activated. If the auto-focus property for a rule is TRUE, then a focus command on
the module in which the rule is defined is automatically executed whenever the rule is activated.
If the auto-focus property for a rule is FALSE, then no action is taken when the rule is activated.
If unspecified, the auto-focus value for a rule defaults to FALSE.
Example
(defrule VIOLATIONS::bad-age
(declare (auto-focus TRUE))
(person (name ?name) (age ?x&:(< ?x 0)))
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=>
(printout t ?name " has a bad age value." crlf))
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Section 6:
Defglobal Construct
With the defglobal construct, global variables can be defined, set, and accessed within the
CLIPS environment. Global variables can be accessed as part of the pattern-matching process,
but changing them does not invoke the pattern-matching process. The bind function is used to
set the value of global variables. Global variables are reset to their original value when the reset
command is performed or when bind is called for the global with no values. This behavior can
be changed using the set-reset-globals function. Global variables can be removed by using the
clear command or the undefglobal command. If the globals item is being watched (see section
13.2), then an informational message will be displayed each time the value of a global variable is
changed.
Syntax
(defglobal [<defmodule-name>] <global-assignment>*)
<global-assignment> ::= <global-variable> = <expression>
<global-variable> ::= ?*<symbol>*
There may be multiple defglobal constructs and any number of global variables may be defined
in each defglobal statement. The optional <defmodule-name> indicates the module in which the
defglobals will be defined. If none is specified, the globals will be placed in the current module.
If a variable was defined in a previous defglobal construct, its value will be replaced by the value
found in the new defglobal construct. If an error is encountered when defining a defglobal
construct, any global variable definitions that occurred before the error was encountered will still
remain in effect.
Commands that operate on defglobals such as ppdefglobal and undefglobal expect the symbolic
name of the global without the astericks (e.g. use the symbol max when you want to refer to the
global variable ?*max*).
Global variables may be used anyplace that a local variable could be used (with two exceptions).
Global variables may not be used as a parameter variable for a deffunction, defmethod, or
message-handler. Global variables may not be used in the same way that a local variable is used
on the LHS of a rule to bind a value. Therefore, the following rule is illegal
(defrule example
(fact ?*x*)
=>)
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The following rule, however, is legal.
(defrule example
(fact ?y&:(> ?y ?*x*))
=>)
Note that this rule will not necessarily be updated when the value of ?*x* is changed. For
example, if ?*x* is 4 and the fact (fact 3) is added, then the rule is not satisfied. If the value of
?*x* is now changed to 2, the rule will not be activated.
Example
(defglobal
?*x* = 3
?*y* = ?*x*
?*z* = (+ ?*x* ?*y*)
?*q* = (create$ a b c))
! Usage Note
The inappropriate use of globals within rules is quite often the first resort of beginning
programmers who have reached an impasse in developing a program because they do not fully
understand how rules and pattern-matching work. As it relates to this issue, the following
sentence from the beginning of this section is important enough to repeat:
Global variables can be accessed as part of the pattern-matching process, but changing them
does not invoke the pattern-matching process.
Facts and instances are the primary mechanism that should be used to pass information from one
rule to another specifically because they do invoke pattern-matching. A change to a slot value of
a fact or instance will trigger pattern-matching ensuring that a rule is aware of the current state of
that fact or instance. Since a change to a global variable does not trigger pattern-matching, it is
possible for a rule to remain activated based on a past value of a global variable that is
undesirable in most situations.
It’s worth pointing out that facts and instances are no less ‘global’ in nature than global
variables. Just as a rule can access any global variable that’s visible (i.e. it hasn’t been hidden
through the use of modules), so too can it access any fact or instance belonging to a deftemplate
or defclass that’s visible. In the case of a fact, one can either pattern-match for the fact on the
LHS of a rule or use the fact-set query functions from the RHS of a rule. In the case of an
instance, pattern-matching and instance-set query functions can also be used, and in addition an
instance can be directly referenced by name just as a global variable can.
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Common Problem
One of the more common situations in which it is tempting to use global variables is collecting a
group of slot values from a fact. First attempts at rules to accomplish this task often loop
endlessly because of rules inadvertently retriggered by changes. For example, the following rule
will loop endlessly because the new collection fact asserted will create an activation with the
same factoid fact that was just added to the collection fact:
(defrule add-factoid
(factoid ?data)
?c <- (collection $?collection)
=>
(retract ?c)
(assert (collection ?collection ?data)))
This problem can be corrected by removing the factoid fact just added to the collection fact:
(defrule add-factoid
?f <- (factoid ?data)
?c <- (collection $?collection)
=>
(retract ?f ?c)
(assert (collection ?collection ?data)))
Retracting the factoid facts, however, isn’t a viable solution if these facts are needed by other
rules. A non-destructive approach makes use of temporary facts created by a helper rule:
(defrule add-factoid-helper
(factoid ?data)
=>
(assert (temp-factoid ?data)))
(defrule add-factoid
?f <- (temp-factoid ?data)
?c <- (collection $?collection)
=>
(retract ?f ?c)
(assert (collection ?collection ?data)))
It certainly looks simpler, however, to use a global variable to collect the slot values:
(defglobal ?*collection* = (create$))
(defrule add-factoid
(factoid ?data)
=>
(bind ?*collection* (create$ ?*collection* ?data)))
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Again, the drawback to this approach is that changes to a global variable do not trigger
pattern-matching, so in spite of its greater complexity the fact-based approach is still preferable.
Although it’s important to understand how each of the previous approaches work, they’re not
practical solutions. If there are 1000 factoid facts, the add-factoid/add-factoid-helper rules will
each fire 1000 times generating and retracting 2000 facts. The best solution is to use the fact-set
query functions to iterate over all of the factoid facts and generate the collection fact as the result
of a single rule firing:
(defrule collect-factoids
(collect-factoids)
=>
(bind ?data (create$))
(do-for-all-facts ((?f factoid)) TRUE
(bind ?data (create$ ?data ?f:implied)))
(assert (collection ?data)))
With this approach, the collection fact is available for pattern-matching with the added benefit
that there are no intermediate results generated in creating the fact. Typically if other rules are
waiting for the finished result of the collection, they would need to have lower salience so that
they aren’t fired for the intermediate results:
(defrule print-factoids
(declare (salience -10))
(collection $?data)
=>
(printout t "The collected data is " ?data crlf))
If the factoid facts are collected by a single rule firing, then the salience declaration is
unnecessary.
Appropriate Uses
The primary use of global variables (in conjunction with rules) is in making a program easier to
maintain. It is a rare situation where a global variable is required in order to solve a problem.
One appropriate use of global variables is defining salience values shared among multiple rules:
(defglobal ?*high-priority* = 100)
(defrule rule-1
(declare (salience ?*high-priority*))
=>)
(defrule rule-2
(declare (salience ?*high-priority*))
=>)
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Another use is defining constants used on the LHS or RHS of a rule:
(defglobal ?*week-days* =
(create$ monday tuesday wednesday thursday friday saturday sunday))
(defrule invalid-day
(day ?day&:(not (member$ ?day ?*week-days*)))
=>
(printout t ?day " is invalid" crlf))
(defrule valid-day
(day ?day&:(member$ ?day ?*week-days*))
=>
(printout t ?day " is valid" crlf))
A third use is passing information to a rule when it is desirable not to trigger pattern-matching. In
the following rule, a global variable is used to determine whether additional debugging
information is printed:
(defglobal ?*debug-print* = nil)
(defrule rule-debug
?f <- (info ?info)
=>
(retract ?f)
(printout ?*debug-print* "Retracting info " ?info crlf))
If ?*debug-print* is set to nil, then the printout statement will not display any information. If the
?*debug-print* is set to t, then debugging information will be sent to the screen. Because
?*debug-print* is a global, it can be changed interactively without causing rules to be
reactivated. This is useful when stepping through a program because it allows the level of
information displayed to be changed without effecting the normal flow of the program.
It’s possible, but a little more verbose, to achieve this same functionality using instances rather
than global variables:
(defclass DEBUG-INFO
(is-a USER)
(slot debug-print))
(definstances debug
([debug-info] of DEBUG-INFO (debug-print nil)))
(defrule rule-debug
?f <- (info ?info)
=>
(retract ?f)
(printout (send [debug-info] get-debug-print) "Retracting info " ?info crlf))
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Unlike fact slots, changes to a slot of an instance won’t trigger pattern matching in a rule unless
the slot is specified on the LHS of that rule, thus you have explicit control over whether an
instance slot triggers pattern-matching. The following rule won’t be retriggered if a change is
made to the debug-print slot:
(defrule rule-debug
?f <- (info ?info)
(object (is-a DEBUG-INFO) (name ?name))
=>
(retract ?f)
(printout (send ?name get-debug-print) "Retracting info " ?info crlf))
This is a generally applicable technique and can be used in many situations to prevent rules from
inadvertently looping when slot values are changed.
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Section 7:
Deffunction Construct
With the deffunction construct, new functions may be defined directly in CLIPS. Deffunctions
are equivalent in use to other functions; see section 2.3.2 for more detail on calling functions in
CLIPS. The only differences between user-defined external functions and deffunctions are that
deffunctions are written in CLIPS and executed by CLIPS interpretively and user-defined
external functions are written in an external language, such as C, and executed by CLIPS
directly. Also, deffunctions allow the addition of new functions without having to recompile and
relink CLIPS.
A deffunction is comprised of five elements: 1) a name, 2) an optional comment, 3) a list of zero
or more required parameters, 4) an optional wildcard parameter to handle a variable number of
arguments and 5) a sequence of actions, or expressions, which will be executed in order when the
deffunction is called.
Syntax
(deffunction <name> [<comment>]
(<regular-parameter>* [<wildcard-parameter>])
<action>*)
<regular-parameter> ::= <single-field-variable>
<wildcard-parameter> ::= <multifield-variable>
A deffunction must have a unique name different from all other system functions and generic
functions. In particular, a deffunction cannot be overloaded like a system function (see section 8
for more detail). A deffunction must be declared prior to being called from another deffunction,
generic function method, object message-handler, rule, or the top level. The only exception is a
self recursive deffunction.
A deffunction may accept exactly or at least a specified number of arguments, depending on
whether a wildcard parameter is used or not. The regular parameters specify the minimum
number of arguments that must be passed to the deffunction. Each of these parameters may be
referenced like a normal single-field variable within the actions of the deffunction. If a wildcard
parameter is present, the deffunction may be passed any number of arguments greater than or
equal to the minimum. If no wildcard parameter is present, then the deffunction must be passed
exactly the number of arguments specified by the regular parameters. All arguments to a
deffunction that do not correspond to a regular parameter are grouped into a multifield value that
can be referenced by the wildcard parameter. The standard CLIPS multifield functions, such as
length and nth, can be applied to the wildcard parameter.
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Example
CLIPS> (clear)
CLIPS>
(deffunction print-args (?a ?b $?c)
(printout t ?a " " ?b " and " (length ?c) " extras: " ?c
crlf))
CLIPS> (print-args 1 2)
1 2 and 0 extras: ()
CLIPS> (print-args a b c d)
a b and 2 extras: (c d)
CLIPS>
When a deffunction is called, its actions are executed in order. The return value of a deffunction
is the evaluation of the last action. If a deffunction has no actions, its return value is the symbol
FALSE. If an error occurs while the deffunction is executing, any actions not yet executed will
be aborted, and the deffunction will return the symbol FALSE.
Deffunctions may be self and mutually recursive. Self recursion is accomplished simply by
calling the deffunction from within its own actions.
Example
(deffunction factorial (?a)
(if (or (not (integerp ?a)) (< ?a 0)) then
(printout t "Factorial Error!" crlf)
else
(if (= ?a 0) then
1
else
(* ?a (factorial (- ?a 1))))))
Mutual recursion between two deffunctions requires a forward declaration of one of the
deffunctions. A forward declaration is simply a declaration of the deffunction without any
actions. In the following example, the deffunction foo is forward declared so that it may be
called by the deffunction bar. Then the deffunction foo is redefined with actions that call the
deffunction bar.
Example
(deffunction foo ())
(deffunction bar ()
(foo))
(deffunction foo ()
(bar))
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Care should be taken with recursive deffunctions; too many levels of recursion can lead to an
overflow of stack memory (especially on PC-type machines).
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Section 8:
Generic Functions
With the defgeneric and defmethod constructs, new generic functions may be written directly in
CLIPS. Generic functions are similar to deffunctions because they can be used to define new
procedural code directly in CLIPS, and they can be called like any other function (see sections
2.3.2 and 7). However, generic functions are much more powerful because they can do different
things depending on the types (or classes) and number of their arguments. For example, a “+”
operator could be defined which performs concatenation for strings but still performs arithmetic
addition for numbers. Generic functions are comprised of multiple components called methods,
where each method handles different cases of arguments for the generic function. A generic
function which has more than one method is said to be overloaded.
Generic functions can have system functions and user-defined external functions as implicit
methods. For example, an overloading of the “+” operator to handle strings consists of two
methods: 1) an implicit one which is the system function handling numerical addition, and 2) an
explicit (user-defined) one handling string concatenation. Deffunctions, however, may not be
methods of generic functions because they are subsumed by generic functions anyway.
Deffunctions are only provided so that basic new functions can be added directly in CLIPS
without the concerns of overloading. For example, a generic function that has only one method
that restricts only the number of arguments is equivalent to a deffunction.
In most cases, generic function methods are not called directly (the function
call-specific-method described in section 12.15.8 can be used to do so, however). CLIPS
recognizes that a function call is generic and uses the generic function’s arguments to find and
execute the appropriate method. This process is termed the generic dispatch.
8.1 Note on the Use of the Term Method
Most OOP systems support procedural behavior of objects either through message-passing (e.g.
Smalltalk) or by generic functions (e.g. CLOS). CLIPS supports both of these mechanisms,
although generic functions are not strictly part of COOL. A generic function may examine the
classes of its arguments but must still use messages within the bodies of its methods to
manipulate any arguments that are instances of user-defined classes. Section 9 gives more details
on COOL. The fact that CLIPS supports both mechanisms leads to confusion in terminology. In
OOP systems that support message-passing only, the term method is used to denote the different
implementations of a message for different classes. In systems that support generic functions
only, however, the term method is used to denote the different implementations of a generic
function for different sets of argument restrictions. To avoid this confusion, the term
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message-handler is used to take the place of method in the context of messages. Thus in
CLIPS, message-handlers denote the different implementations of a message for different
classes, and methods denote the different implementations of a generic function for different
sets of argument restrictions.
8.2 Performance Penalty of Generic Functions
A call to a generic function is computationally more expensive than a call to a system function,
user-defined external function or deffunction. This is because CLIPS must first examine the
function arguments to determine which method is applicable. A performance penalty of
15%-20% is not unexpected. Thus, generic functions should not be used for routines for which
time is critical, such as routines that are called within a while loop, if at all possible. Also,
generic functions should always have at least two methods. Deffunctions or user-defined external
functions should be used when overloading is not required. A system or user-defined external
function that is not overloaded will, of course, execute as quickly as ever, since the generic
dispatch is unnecessary.
8.3 Order Dependence of Generic Function Definitions
If a construct which uses a system or user-defined external function is loaded before a generic
function that uses that function as an implicit method, all calls to that function from that
construct will bypass the generic dispatch. For example, if a generic function which overloads
the “+” operator is defined after a rule which uses the “+” operator, that rule will always call the
“+” system function directly. However, similar rules defined after the generic function will use
the generic dispatch.
8.4 Defining a New Generic Function
A generic function is comprised of a header (similar to a forward declaration) and zero or more
methods. A generic function header can either be explicitly declared by the user or implicitly
declared by the definition of at least one method. A method is comprised of six elements: 1) a
name (which identifies to which generic function the method belongs), 2) an optional index, 3)
an optional comment, 4) a set of parameter restrictions, 5) an optional wildcard parameter
restriction to handle a variable number of arguments and 6) a sequence of actions, or
expressions, which will be executed in order when the method is called. The parameter
restrictions are used by the generic dispatch to determine a method’s applicability to a set of
arguments when the generic function is actually called. The defgeneric construct is used to
specify the generic function header, and the defmethod construct is used for each of the generic
function’s methods.
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Syntax
(defgeneric <name> [<comment>])
(defmethod <name> [<index>] [<comment>]
(<parameter-restriction>* [<wildcard-parameter-restriction>])
<action>*)
<parameter-restriction> ::=
<single-field-variable> |
(<single-field-variable> <type>* [<query>])
<wildcard-parameter-restriction> ::=
<multifield-variable> |
(<multifield-variable> <type>* [<query>])
<type> ::= <class-name>
<query> ::= <global-variable> |
<function-call>
A generic function must be declared, either by a header or a method, prior to being called from
another generic function method, deffunction, object message-handler, rule, or the top level. The
only exception is a self recursive generic function.
8.4.1 Generic Function Headers
A generic function is uniquely identified by name. In order to reference a generic function in
other constructs before any of its methods are declared, an explicit header is necessary.
Otherwise, the declaration of the first method implicitly creates a header. For example, two
generic functions whose methods mutually call the other generic function (mutually recursive
generic functions) would require explicit headers.
8.4.2 Method Indices
A method is uniquely identified by name and index, or by name and parameter restrictions. Each
method for a generic function is assigned a unique integer index within the group of all methods
for that generic function. Thus, if a new method is defined which has exactly the same name and
parameter restrictions as another method, CLIPS will automatically replace the older method.
However, any difference in parameter restrictions will cause the new method to be defined in
addition to the older method. To replace an old method with one that has different parameter
restrictions, the index of the old method can be explicitly specified in the new method definition.
However, the parameter restrictions of the new method must not match that of another method
with a different index. If an index is not specified, CLIPS assigns an index that has never been
used by any method (past or current) of this generic function. The index assigned by CLIPS can
be determined with the list-defmethods command (see section 13.10.4).
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8.4.3 Method Parameter Restrictions
Each parameter for a method can be defined to have arbitrarily complex restrictions or none at
all. A parameter restriction is applied to a generic function argument at run-time to determine if a
particular method will accept the argument. A parameter can have two types of restrictions: type
and query. A type restriction constrains the classes of arguments that will be accepted for a
parameter. A query restriction is a user-defined boolean test which must be satisfied for an
argument to be acceptable. The complexity of parameter restrictions directly affects the speed of
the generic dispatch.
A parameter that has no restrictions means that the method will accept any argument in that
position. However, each method of a generic function must have parameter restrictions that make
it distinguishable from all of the other methods so that the generic dispatch can tell which one to
call at run-time. If there are no applicable methods for a particular generic function call, CLIPS
will generate an error (see section 8.5.4 for more detail).
A type restriction allows the user to specify a list of types (or classes), one of which must match
(or be a superclass of) the class of the generic function argument. If COOL is not installed in the
current CLIPS configuration, the only types (or classes) available are: OBJECT, PRIMITIVE,
LEXEME, SYMBOL, STRING, NUMBER, INTEGER, FLOAT, MULTIFIELD,
FACT-ADDRESS and EXTERNAL-ADDRESS. Section 9 describes each of these system
classes. With COOL, INSTANCE, INSTANCE-ADDRESS, INSTANCE-NAME, USER,
INITIAL-OBJECT and any user-defined classes are also available. Generic functions that use
only the first group of types in their methods will work the same whether COOL is installed or
not. The classes in a type restriction must be defined already, since they are used to predetermine
the precedence between a generic function’s methods (see section 8.5.2 for more detail).
Redundant classes are not allowed in restriction class lists. For example, the following method
parameter’s type restriction is redundant since INTEGER is a subclass of NUMBER.
Example
(defmethod foo ((?a INTEGER NUMBER)))
If the type restriction (if any) is satisfied for an argument, then a query restriction (if any) will be
applied. The query restriction must either be a global variable or a function call. CLIPS evaluates
this expression, and if it evaluates to anything but the symbol FALSE, the restriction is
considered satisfied. Since a query restriction is not always satisfied, queries should not have any
side-effects, for they will be evaluated for a method that may not end up being applicable to the
generic function call. Since parameter restrictions are examined from left to right, queries that
involve multiple parameters should be included with the rightmost parameter. This insures that
all parameter type restrictions have already been satisfied. For example, the following method
delays evaluation of the query restriction until the classes of both arguments have been verified.
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Example
(defmethod foo ((?a INTEGER) (?b INTEGER (> ?a ?b))))
If the argument passes all these tests, it is deemed acceptable to a method. If all generic function
arguments are accepted by a method’s restrictions, the method itself is deemed applicable to the
set of arguments. When more than one method is applicable to a set of arguments, the generic
dispatch must determine an ordering among them and execute the first one in that ordering.
Method precedence is used for this purpose and will be discussed in section 8.5.2.
Example
In the following example, the first call to the generic function “+” executes the system operator
“+”, an implicit method for numerical addition. The second call executes the explicit method for
string concatenation, since there are two arguments and they are both strings. The third call
generates an error because the explicit method for string concatenation only accepts two
arguments and the implicit method for numerical addition does not accept strings at all.
CLIPS> (clear)
CLIPS>
(defmethod + ((?a STRING) (?b STRING))
(str-cat ?a ?b))
CLIPS> (+ 1 2)
3
CLIPS> (+ "foo" "bar")
"foobar"
CLIPS> (+ "foo" "bar" "woz")
[GENRCEXE1] No applicable methods for +.
FALSE
CLIPS>
8.4.4 Method Wildcard Parameter
A method may accept exactly or at least a specified number of arguments, depending on whether
a wildcard parameter is used or not. The regular parameters specify the minimum number of
arguments that must be passed to the method. Each of these parameters may be referenced like a
normal single-field variable within the actions of the method. If a wildcard parameter is present,
the method may be passed any number of arguments greater than or equal to the minimum. If no
wildcard parameter is present, then the method must be passed exactly the number of arguments
specified by the regular parameters. Method arguments that do not correspond to a regular
parameter can be grouped into a multifield value that can be referenced by the wildcard
parameter within the body of the method. The standard CLIPS multifield functions, such as
length$ and expand$, can be applied to the wildcard parameter.
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If multifield values are passed as extra arguments, they will all be merged into one multifield
value referenced by the wildcard parameter. This is because CLIPS does not support nested
multifield values.
Type and query restrictions can be applied to arguments grouped in the wildcard parameter
similarly to regular parameters. Such restrictions apply to each individual field of the resulting
multifield value (not the entire multifield). However, expressions involving the wildcard
parameter variable may be used in the query. In addition, a special variable may be used in query
restrictions on the wildcard parameter to refer to the individual arguments grouped into the
wildcard: ?current-argument. This variable is only in scope within the query and has no
meaning in the body of the method. For example, to create a version of the ‘+’ operator which
acts differently for sums of all even integers:
Example
CLIPS>
(defmethod +
(($?any INTEGER (evenp ?current-argument)))
(div (call-next-method) 2))
CLIPS> (+ 1 2)
3
CLIPS> (+ 4 6 4)
7
CLIPS>
It is important to emphasize that query and type restrictions on the wildcard parameter are
applied to every argument grouped in the wildcard. Thus in the following example, the > and
length$ functions are actually called three times, since there are three arguments:
Example
CLIPS> (defmethod foo (($?any (> (length$ ?any) 2))) yes)
CLIPS> (foo 1 red 3)
yes
CLIPS>
In addition, a query restriction will never be examined if there are no arguments in the wildcard
parameter range. For example, the the previous methodwould be applicable to a call to the
generic function with no arguments because the query restriction is never evaluated:
Example
CLIPS> (foo)
yes
CLIPS>
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Typically query restrictions applied to the entire wildcard parameter are testing the cardinality
(the number of arguments passed to the method). In cases like this where the type is irrelevant to
the test, the query restriction can be attached to a regular parameter instead to improve
performance (see section 8.5.1). Thus the previous method could be improved as follows:
Example
CLIPS> (clear)
CLIPS> (defmethod foo ((?arg (> (length$ ?any) 1)) $?any) yes)
CLIPS> (foo)
[GENRCEXE1] No applicable methods for foo.
FALSE
CLIPS>
This approach should not be used if the types of the arguments grouped by the wildcard must be
verified prior to safely evaluating the query restriction.
8.5 Generic Dispatch
When a generic function is called, CLIPS selects the method for that generic function with
highest precedence for which parameter restrictions are satisfied by the arguments. This method
is executed, and its value is returned as the value of the generic function. This entire process is
referred to as the generic dispatch. Below is a flow diagram summary:
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The solid arrows indicate automatic control transfer by the generic dispatch. The dashed arrows
indicate control transfer that can only be accomplished by the use or lack of the use of call-next-
method or override-next-method.
8.5.1 Applicability of Methods Summary
An explicit (user-defined) method is applicable to a generic function call if the following three
conditions are met: 1) its name matches that of the generic function, 2) it accepts at least as many
arguments as were passed to the generic function, and 3) every argument of the generic function
satisfies the corresponding parameter restriction (if any) of the method.
Method restrictions are examined from left to right. As soon as one restriction is not satisfied, the
method is abandoned, and the rest of the restrictions (if any) are not examined.
DONE: Return control and values to caller.
ERROR: There are no applicable methods for this
generic function. Return control to caller.
START: Input is a ranked list of applicable methods.
METHOD STEP: Are there any uncalled methods?
YES: Call the next most specific method.
If the body uses call-next-method or
override-next-method, repeat this step.
Else go to DONE.
When body returns, return its values to caller.
NO: Go to ERROR.
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When a standard CLIPS system function is overloaded, CLIPS forms an implicit method
definition corresponding to that system function. This implicit method is derived from the
argument restriction string for the external DefineFunction2 call defining that function to CLIPS
(see the Advanced Programming Guide). This string can be accessed with the function
get-function-restrictions. The specification of this implicit method can be examined with the
list-defmethods or get-method-restrictions functions. The method that CLIPS will form for a
system function can be derived by the user from the BNF given in this document. For example,
(+ <number> <number>+)
would yield the following method for the ‘+’ function:
(defmethod + ((?first NUMBER) (?second NUMBER) ($?rest NUMBER))
...)
The method definition is used to determine the applicability and precedence of the system
function to the generic function call.
The following system functions cannot be overloaded, and CLIPS will generate an error if an
attempt is made to do so.
active-duplicate-instance
find-instance
active-initialize-instance
foreach
active-make-instance
if
active-message-duplicate-instance
make-instance
active-message-modify-instance
initialize-instance
active-modify-instance
loop-for-count
any-instancep
message-duplicate-instance
assert
message-modify-instance
bind
modify
break
modify-instance
call-next-handler
next-handlerp
call-next-method
next-methodp
call-specific-method
object-pattern-match-delay
delayed-do-for-all-instances
override-next-handler
do-for-all-instances
override-next-method
do-for-instance
progn
duplicate
progn$
duplicate-instance
return
expand$
switch
find-all-instances
while
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8.5.2 Method Precedence
When two or more methods are applicable to a particular generic function call, CLIPS must pick
the one with highest precedence for execution. Method precedence is determined when a
method is defined; the list-defmethods function can be used to examine the precedence of
methods for a generic function (see section 13.10).
The precedence between two methods is determined by comparing their parameter restrictions.
In general, the method with the most specific parameter restrictions has the highest precedence.
For example, a method that demands an integer for a particular argument will have higher
precedence than a method which only demands a number. The exact rules of precedence between
two methods are given in order below; the result of the first rule that establishes precedence is
taken.
1) The parameter restrictions of both methods are positionally compared from left to right. In
other words, the first parameter restriction in the first method is matched against the first
parameter restriction in the second method, and so on. The comparisons between these pairs
of parameter restrictions from the two methods determine the overall precedence between
the two methods. The result of the first pair of parameter restrictions that specifies
precedence is taken. The following rules are applied in order to a parameter pair; the result
of the first rule that establishes precedence is taken.
a) A regular parameter has precedence over a wildcard parameter.
b) The most specific type restriction on a particular parameter has priority. A class is more
specific than any of its superclasses.
c) A parameter with a query restriction has priority over one that does not.
2) The method with the greater number of regular parameters has precedence.
3) A method without a wildcard parameter has precedence over one that does
4) A method defined before another one has priority.
If there are multiple classes on a single restriction, determining specificity is slightly more
complicated. Since all precedence determination is done when the new method is defined, and
the actual class of the generic function argument will not be known until run-time, arbitrary (but
deterministic) rules are needed for determining the precedence between two class lists. The two
class lists are examined by pairs from left to right, e.g. the pair of first classes from both lists, the
pair of second classes from both lists and so on. The first pair containing a class and its
superclass specify precedence. The class list containing the subclass has priority. If no class pairs
specify precedence, then the shorter class list has priority. Otherwise, the class lists do not
specify precedence between the parameter restrictions.
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Example 1
; The system operator '+' is an implicit method ; #1
; Its definition provided by the system is:
; (defmethod + ((?a NUMBER) (?b NUMBER) ($?rest NUMBER)))
(defmethod + ((?a NUMBER) (?b INTEGER))) ; #2
(defmethod + ((?a INTEGER) (?b INTEGER))) ; #3
(defmethod + ((?a INTEGER) (?b NUMBER))) ; #4
(defmethod + ((?a NUMBER) (?b NUMBER) ; #5
($?rest PRIMITIVE)))
(defmethod + ((?a NUMBER) ; #6
(?b INTEGER (> ?b 2))))
(defmethod + ((?a INTEGER (> ?a 2)) ; #7
(?b INTEGER (> ?b 3))))
(defmethod + ((?a INTEGER (> ?a 2)) ; #8
(?b NUMBER)))
The precedence would be: #7,#8,#3,#4,#6,#2,#1,#5. The methods can be immediately partitioned
into three groups of decreasing precedence according to their restrictions on the first parameter:
A) methods which have a query restriction and a type restriction of INTEGER (#7,#8), B)
methods which have a type restriction of INTEGER (#3,#4), and C) methods which have a type
restriction of NUMBER (#1,#2,#5,#6). Group A has precedence over group B because
parameters with query restrictions have priority over those that do not. Group B has precedence
over group C because INTEGER is a subclass of NUMBER. Thus, the ordering so far is:
(#7,#8),(#3,#4),(#1,#2,#5,#6). Ordering between the methods in a particular set of parentheses is
not yet established.
The next step in determining precedence between these methods considers their restrictions on
the second parameter. #7 has priority over #8 because INTEGER is a subclass of NUMBER. #3
has priority over #4 because INTEGER is a subclass of NUMBER. #6 and #2 have priority over
#1 and #5 because INTEGER is a subclass of NUMBER. #6 has priority over #2 because it has a
query restriction and #2 does not. Thus the ordering is now: #7,#8,#3,#4,#6,#2,(#1,#5).
The restriction on the wildcard argument yields that #1 (the system function implicit method) has
priority over #5 since NUMBER is a sublclass of PRIMITIVE. This gives the final ordering:
#7,#8,#3,#4,#6,#2,#1,#5.
Example 2
(defmethod foo ((?a NUMBER STRING))) ; #1
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(defmethod foo ((?a INTEGER LEXEME))) ; #2
The precedence would be #2,#1. Although STRING is a subclass of LEXEME, the ordering is
still #2,#1 because INTEGER is a subclass of NUMBER, and NUMBER/INTEGER is the
leftmost pair in the class lists.
Example 3
(defmethod foo ((?a MULTIFIELD STRING))) ; #1
(defmethod foo ((?a LEXEME))) ; #2
The precedence would be #2,#1 because the classes of the first pair in the type restriction
(MULTIFIELD/LEXEME) are unrelated and #2 has fewer classes in its class list.
Example 4
(defmethod foo ((?a INTEGER LEXEME))) ; #1
(defmethod foo ((?a STRING NUMBER))) ; #2
Both pairs of classes (INTEGER/STRING and LEXEME/NUMBER) are unrelated, and the class
lists are of equal length. Thus, the precedence is taken from the order of definition: #1,#2.
8.5.3 Shadowed Methods
If one method must be called by another method in order to be executed, the first function or
method is a said to be shadowed by the second method. Normally, only one method or system
function will be applicable to a particular generic function call. If there is more than one
applicable method, the generic dispatch will only execute the one with highest precedence.
Letting the generic dispatch automatically handle the methods in this manner is called the
declarative technique, for the declarations of the method restrictions dictate which method gets
executed in specific circumstances. However, the functions call-next-method and
override-next-method (see section 12.15.6 and 12.15.7) may also be used which allow a method
to execute the method that it is shadowing. This is called the imperative technique, since the
method execution itself plays a role in the generic dispatch. This is not recommended unless it is
absolutely necessary. In most circumstances, only one piece of code should need to be executed
for a particular set of arguments. Another imperative technique is to use the function
call-specific-method to override method precedence (see section 12.15.8)
8.5.4 Method Execution Errors
If an error occurs while any method for a generic function call is executing, any actions in the
current method not yet executed will be aborted, any methods not yet called will be aborted, and
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the generic function will return the symbol FALSE. The lack of any applicable methods for a set
of generic function arguments is considered a method execution error.
8.5.5 Generic Function Return Value
The return value of a generic function is the return value of the applicable method with the
highest precedence. Each applicable method that is executed can choose to ignore or capture the
return value of any method that it is shadowing.
The return value of a particular method is the last action evaluated by that method.
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Section 9:
CLIPS Object Oriented Language
This section provides the comprehensive details of the CLIPS Object-Oriented Language
(COOL). Sections 2.3.1, 2.4.2 and 2.5.2.3 explain object references and structure. Section 2.6
gives a high level overview of COOL. This section assumes a complete understanding of the
material given in the listed sections.
9.1 Background
COOL is a hybrid of features from many different OOP systems as well as new ideas. For
example, object encapsulation concepts are similar to those in Smalltalk, and the Common Lisp
Object System (CLOS) provides the basis for multiple inheritance rules. A mixture of ideas from
Smalltalk, CLOS and other systems form the foundation of messages. Section 8.1 explains an
important contrast between the terms method and message-handler in CLIPS.
9.2 Predefined System Classes
COOL provides seventeen system classes: OBJECT, USER, INITIAL-OBJECT, PRIMITIVE,
NUMBER, INTEGER, FLOAT, INSTANCE, INSTANCE-NAME, INSTANCE-ADDRESS,
ADDRESS, FACT-ADDRESS, EXTERNAL-ADDRESS, MULTIFIELD, LEXEME, SYMBOL
and STRING. The user may not delete or modify any of these classes. The diagram illustrates the
inheritance relationships between these classes.
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All of these system classes except INITIAL-OBJECT are abstract classes, which means that
their only use is for inheritance (direct instances of this class are illegal). None of these classes
have slots, and, except for the class USER, none of them have message-handlers. However, the
user may explicitly attach message-handlers to all of the system classes except for INSTANCE,
INSTANCE-ADDRESS and INSTANCE-NAME. The OBJECT class is a superclass of all other
classes, including user-defined classes. All user-defined classes should (but are not required to)
inherit directly or indirectly from the class USER, since this class has all of the standard system
message-handlers, such as initialization and deletion, attached to it. Section 9.4 describes these
system message-handlers.
The PRIMITIVE system class and all of its subclasses are provided mostly for use in generic
function method restrictions, but message-handlers and new subclasses may be attached if
desired. However, the three primitive system classes INSTANCE, INSTANCE-ADDRESS and
INSTANCE-NAME are provided strictly for use in methods (particularly in forming implicit
methods for overloaded system functions - see section 8.5.1) and as such cannot have subclasses
or message-handlers attached to them.
OBJECT
USER
INITIAL-OBJECT
PRIMITIVE
NUMBER
FLOAT
INSTANCE-NAME
INSTANCE
INTEGER
INSTANCE-ADDRESS FACT-ADDRESS EXTERNAL-ADDRESS
ADDRESS
MULTIFIELD LEXEME
SYMBOL STRING
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The INITIAL-OBJECT class is provided for use by the default definstances initial-object in
creating the default instance [initial-object] during the reset command. This system class is
concrete and reactive to pattern-matching on the LHS of rules but is in other respects exactly
like the system class USER. The instance [initial-object] is for use by the initial-object pattern
(see section 5.4.9).
9.3 Defclass Construct
A defclass is a construct for specifying the properties (slots) and behavior (message-handlers) of
a class of objects. A defclass consists of five elements: 1) a name, 2) a list of superclasses from
which the new class inherits slots and message-handlers, 3) a specifier saying whether or not the
creation of direct instances of the new class is allowed, 4) a specifier saying whether or not
instances of this class can match object patterns on the LHS of rules and 5) a list of slots specific
to the new class. All user-defined classes must inherit from at least one class, and to this end
COOL provides predefined system classes for use as a base in the derivation of new classes.
Any slots explicitly given in the defclass override those gotten from inheritance. COOL applies
rules to the list of superclasses to generate a class precedence list (see section 9.3.1) for the new
class. Facets (see section 9.3.3) further describe slots. Some examples of facets include: default
value, cardinality, and types of access allowed.
Syntax
Defaults are in bold italics.
(defclass <name> [<comment>]
(is-a <superclass-name>+)
[<role>]
[<pattern-match-role>]
<slot>*
<handler-documentation>*)
<role> ::= (role concrete | abstract)
<pattern-match-role>
::= (pattern-match reactive | non-reactive)
<slot> ::= (slot <name> <facet>*) |
(single-slot <name> <facet>*) |
(multislot <name> <facet>*)
<facet> ::= <default-facet> | <storage-facet> |
<access-facet> | <propagation-facet> |
<source-facet> | <pattern-match-facet> |
<visibility-facet> | <create-accessor-facet>
<override-message-facet> | <constraint-attributes>
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<default-facet> ::=
(default
?DERIVE
| ?NONE | <expression>*) |
(default-dynamic <expression>*)
<storage-facet> ::= (storage
local
| shared)
<access-facet>
::= (access
read-write
| read-only | initialize-only)
<propagation-facet> ::= (propagation
inherit
| no-inherit)
<source-facet> ::= (source
exclusive
| composite)
<pattern-match-facet>
::= (pattern-match
reactive
| non-reactive)
<visibility-facet> ::= (visibility
private
| public)
<create-accessor-facet>
::= (create-accessor ?NONE | read | write |
read-write
)
<override-message-facet>
::= (override-message
?DEFAULT
| <message-name>)
<handler-documentation>
::= (message-handler <name> [<handler-type>])
<handler-type> ::=
primary
| around | before | after
Redefining an existing class deletes the current subclasses and all associated message-handlers.
An error will occur if instances of the class or any of its subclasses exist.
9.3.1 Multiple Inheritance
If one class inherits from another class, the first class is a subclass of the second class, and the
second class is a superclass of the first class. Every user-defined class must have at least one
direct superclass, i.e. at least one class must appear in the is-a portion of the defclass. Multiple
inheritance occurs when a class has more than one direct superclass. COOL examines the direct
superclass list for a new class to establish a linear ordering called the class precedence list. The
new class inherits slots and message-handlers from each of the classes in the class precedence
list. The word precedence implies that slots and message-handlers of a class in the list override
conflicting definitions of another class found later in the list. A class that comes before another
class in the list is said to be more specific. All class precedence lists will terminate in the system
class OBJECT, and most (if not all) class precedence lists for user-defined classes will terminate
in the system classes USER and OBJECT. The class precedence list can be listed using the
describe-class function (see section 13.11.1.4).
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9.3.1.1 Multiple Inheritance Rules
COOL uses the inheritance hierarchy of the direct superclasses to determine the class precedence
list for a new class. COOL recursively applies the following two rules to the direct superclasses:
1) A class has higher precedence than any of its superclasses.
2) A class specifies the precedence between its direct superclasses.
If more than one class precedence list would satisfy these rules, COOL chooses the one most
similar to a strict preorder depth-first traversal. This heuristic attempts to preserve “family trees”
to the greatest extent possible. For example, if a child inherited genetic traits from a mother and
father, and the mother and father each inherited traits from their parents, the child’s class
precedence list would be: child mother maternal-grandmother maternal-grandfather father
paternal-grandmother paternal-grandfather. There are other orderings which would satisfy the
rules (such as child mother father paternal-grandfather maternal-grandmother
paternal-grandmother maternal-grandfather), but COOL chooses the one which keeps the family
trees together as much as possible.
Example 1
(defclass A (is-a USER))
Class A directly inherits information from the class USER. The class precedence list for A is: A
USER OBJECT.
Example 2
(defclass B (is-a USER))
Class B directly inherits information from the class USER. The class precedence list for B is: B
USER OBJECT.
Example 3
(defclass C (is-a A B))
Class C directly inherits information from the classes A and B. The class precedence list for C is:
C A B USER OBJECT.
Example 4
(defclass D (is-a B A))
Class D directly inherits information from the classes B and A. The class precedence list for D is:
D B A USER OBJECT.
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Example 5
(defclass E (is-a A C))
By rule #2, A must precede C. However, C is a subclass of A and cannot succeed A in a
precedence list without violating rule #1. Thus, this is an error.
Example 6
(defclass E (is-a C A))
Specifying that E inherits from A is extraneous, since C inherits from A. However, this definition
does not violate any rules and is acceptable. The class precedence list for E is: E C A B USER
OBJECT.
Example 7
(defclass F (is-a C B))
Specifying that F inherits from B is extraneous, since C inherits from B. The class precedence
list for F is: F C A B USER OBJECT. The superclass list says B must follow C in F’s class
precedence list but not that B must immediately follow C.
Example 8
(defclass G (is-a C D))
This is an error, for it violates rule #2. The class precedence of C says that A should precede B,
but the class precedence list of D says the opposite.
Example 9
(defclass H (is-a A))
(defclass I (is-a B))
(defclass J (is-a H I A B))
The respective class precedence lists of H and I are: H A USER OBJECT and I B USER
OBJECT. If J did not have A and B as direct superclasses, J could have one of three possible
class precedence lists: J H A I B USER OBJECT, J H I A B USER OBJECT or J H I B A USER
OBJECT. COOL would normally pick the first list since it preserves the family trees (H A and I
B) to the greatest extent possible. However, since J inherits directly from A and B, rule #2
dictates that the class precedence list must be J H I A B USER OBJECT.
! Usage Note
For most practical applications of multiple inheritance, the order in which the superclasses are
specified should not matter. If you create a class using multiple inheritance and the order of the
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classes specified in the is-a attribute effects the behavior of the class, you should consider
whether your program design is needlessly complex.
9.3.2 Class Specifiers
9.3.2.1 Abstract and Concrete Classes
An abstract class is intended for inheritance only, and no direct instances of this class can be
created. A concrete class can have direct instances. Using the abstract role specifier in a defclass
will cause COOL to generate an error if make-instance is ever called for this class. If the
abstract or concrete descriptor for a class is not specified, it is determined by inheritance. For the
purpose of role inheritance, system defined classes behave as concrete classes. Thus a class
which inherits from USER will be concrete if no role is specified.
9.3.2.2 Reactive and Non-Reactive Classes
Objects of a reactive class can match object patterns in a rule. Objects of a non-reactive class
cannot match object patterns in a rule and are not considered when the list of applicable classes
are determined for an object pattern. An abstract class cannot be reactive. If the reactive or
non-reactive descriptor for a class is not specified, it is determined by inheritance. For the
purpose of pattern-match inheritance, system defined classes behave as reactive classes unless
the inheriting class is abstract.
9.3.3 Slots
Slots are placeholders for values associated with instances of a user-defined class. Each instance
has a copy of the set of slots specified by the immediate class as well as any obtained from
inheritance. Only available memory limits the number of slots. The name of a slot may be any
symbol with the exception of the keywords is-a and name which are reserved for use in object
patterns.
To determine the set of slots for an instance, the class precedence list for the instance’s class is
examined in order from most specific to most general (left to right). A class is more specific than
its superclasses. Slots specified in any of the classes in the class precedence list are given to the
instance, with the exception of no-inherit slots (see section 9.3.3.5). If a slot is inherited from
more than one class, the definition given by the more specific class takes precedence, with the
exception of composite slots (see section 9.3.3.6).
Example
(defclass A (is-a USER)
(slot fooA)
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(slot barA))
(defclass B (is-a A)
(slot fooB)
(slot barB))
The class precedence list of A is: A USER OBJECT. Instances of A will have two slots: fooA
and barA. The class precedence list of B is: B A USER OBJECT. Instances of B will have four
slots: fooB, barB, fooA and barA.
Just as slots make up classes, facets make up slots. Facets describe various features of a slot that
hold true for all objects which have the slot: default value, storage, access, inheritance
propagation, source of other facets, pattern-matching reactivity, visibility to subclass
message-handlers, the automatic creation of message-handlers to access the slot, the name of the
message to send to set the slot and constraint information. Each object can still have its own
value for a slot, with the exception of shared slots (see section 9.3.3.3).
9.3.3.1 Slot Field Type
A slot can hold either a single-field or multifield value. By default, a slot is single-field. The
keyword multislot specifies that a slot can hold a multifield value comprised of zero or more
fields, and the keywords slot or single-slot specify that the slot can hold one value. Multifield
slot values are stored as multifield values and can be manipulated with the standard multifield
functions, such as nth$ and length$, once they are retrieved via messages. COOL also provides
functions for setting multifield slots, such as slot-insert$ (see section 12.16.4.12.2). Single-field
slots are stored as a CLIPS primitive type, such as integer or string.
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(multislot foo
(default abc def ghi)))
CLIPS> (make-instance a of A)
[a]
CLIPS> (nth$ 2 (send [a] get-foo))
def
CLIPS>
9.3.3.2 Default Value Facet
The default and default-dynamic facets can be used to specify an initial value given to a slot
when an instance of the class is created or initialized. By default, a slot will have a default value
that is derived from the slot’s constraint facets (see sections 9.3.3.11 and 11.5). Default values
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are directly assigned to slots without the use of messages, unlike slot overrides in a
make-instance call (see section 9.6.1).
The default facet is a static default: the specified expression is evaluated once when the class is
defined, and the result is stored with the class. This result is assigned to the appropriate slot when
a new instance is created. If the keyword ?DERIVE is used for the default value, then a default
value is derived from the constraints for the slot (see section 11.5 for more details). By default,
the default attribute for a slot is (default ?DERIVE). If the keyword ?NONE is used for the
default value, then the slot is not assigned a default value. Using this keyword causes
make-instance to require a slot-override for that slot when an instance is created. Note that in
CLIPS 6.0, a slot now has a default even if one is not explicitly specified (unlike CLIPS 5.1).
This could cause different behavior for CLIPS 5.1 programs using the initialize-instance
function. The ?NONE keyword can be used to recover the original behavior for classes.
The default-dynamic facet is a dynamic default: the specified expression is evaluated every time
an instance is created, and the result is assigned to the appropriate slot.
Example
CLIPS> (clear)
CLIPS> (setgen 1)
1
CLIPS>
(defclass A (is-a USER)
(slot foo (default-dynamic (gensym))))
CLIPS> (make-instance a1 of A)
[a1]
CLIPS> (make-instance a2 of A)
[a2]
CLIPS> (send [a1] get-foo)
gen1
CLIPS> (send [a2] get-foo)
gen2
CLIPS>
9.3.3.3 Storage Facet
The actual value of an instance’s copy of a slot can either be stored with the instance or with the
class. The local facet specifies that the value be stored with the instance, and this is the default.
The shared facet specifies that the value be stored with the class. If the slot value is locally
stored, then each instance can have a separate value for the slot. However, if the slot value is
stored with the class, all instances will have the same value for the slot. Anytime the value is
changed for a shared slot, it will be changed for all instances with that slot.
A shared slot will always pick up a dynamic default value from a defclass when an instance is
created or initialized, but the shared slot will ignore a static default value unless it does not
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currently have a value. Any changes to a shared slot will cause pattern-matching for rules to be
updated for all reactive instances containing that slot.
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot foo (storage shared)
(default 1))
(slot bar (storage shared)
(default-dynamic 2))
(slot woz (storage local)))
CLIPS> (make-instance a of A)
[a]
CLIPS> (send [a] print)
[a] of A
(foo 1)
(bar 2)
(woz nil)
CLIPS> (send [a] put-foo 56)
56
CLIPS> (send [a] put-bar 104)
104
CLIPS> (make-instance b of A)
[b]
CLIPS> (send [b] print)
[b] of A
(foo 56)
(bar 2)
(woz nil)
CLIPS> (send [b] put-foo 34)
34
CLIPS> (send [b] put-woz 68)
68
CLIPS> (send [a] print)
[a] of A
(foo 34)
(bar 2)
(woz nil)
CLIPS> (send [b] print)
[b] of A
(foo 34)
(bar 2)
(woz 68)
CLIPS>
9.3.3.4 Access Facet
There are three types of access facets which can be specified for a slot: read-write, read-only,
and initialize-only. The read-write facet is the default and says that a slot can be both written
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and read. The read-only facet says the slot can only be read; the only way to set this slot is with
default facets in the class definition. The initialize-only facet is like read-only except that the
slot can also be set by slot overrides in a make-instance call (see section 9.6.1) and init
message-handlers (see section 9.4). These privileges apply to indirect access via messages as
well as direct access within message-handler bodies (see section 9.4). Note: a read-only slot that
has a static default value will implicitly have the shared storage facet.
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot foo (access read-write))
(slot bar (access read-only) (default abc))
(slot woz (access initialize-only)))
CLIPS>
(defmessage-handler A put-bar (?value)
(dynamic-put (sym-cat bar) ?value))
CLIPS> (make-instance a of A (bar 34))
[MSGFUN3] bar slot in [a] of A: write access denied.
[PRCCODE4] Execution halted during the actions of message-handler put-bar primary
in class A
FALSE
CLIPS> (make-instance a of A (foo 34) (woz 65))
[a]
CLIPS> (send [a] put-bar 1)
[MSGFUN3] bar slot in [a] of A: write access denied.
[PRCCODE4] Execution halted during the actions of message-handler put-bar primary
in class A
FALSE
CLIPS> (send [a] put-woz 1)
[MSGFUN3] woz slot in [a] of A: write access denied.
[PRCCODE4] Execution halted during the actions of message-handler put-bar primary
in class A
FALSE
CLIPS> (send [a] print)
[a] of A
(foo 34)
(bar abc)
(woz 65)
CLIPS>
9.3.3.5 Inheritance Propagation Facet
An inherit facet says that a slot in a class can be given to instances of other classes that inherit
from the first class. This is the default. The no-inherit facet says that only direct instances of this
class will get the slot.
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Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot foo (propagation inherit))
(slot bar (propagation no-inherit)))
CLIPS> (defclass B (is-a A))
CLIPS> (make-instance a of A)
[a]
CLIPS> (make-instance b of B)
[b]
CLIPS> (send [a] print)
[a] of A
(foo nil)
(bar nil)
CLIPS> (send [b] print)
[b] of B
(foo nil)
CLIPS>
9.3.3.6 Source Facet
When obtaining slots from the class precedence list during instance creation, the default behavior
is to take the facets from the most specific class that gives the slot and give default values to any
unspecified facets. This is the behavior specified by the exclusive facet. The composite facet
causes facets which are not explicitly specified by the most specific class to be taken from the
next most specific class. Thus, in an overlay fashion, the facets of an instance’s slot can be
specified by more than one class. Note that even though facets may be taken from superclasses,
the slot is still considered to reside in the new class for purposes of visibility (see section
9.3.3.8). One good example of a use of this feature is to pick up a slot definition and change only
its default value for a new derived class.
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(multislot foo (access read-only)
(default a b c)))
CLIPS>
(defclass B (is-a A)
(slot foo (source composite) ; multiple and read-only
; from class A
(default d e f)))
CLIPS> (describe-class B)
================================================================================
********************************************************************************
Concrete: direct instances of this class can be created.
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Reactive: direct instances of this class can match defrule patterns.
Direct Superclasses: A
Inheritance Precedence: B A USER OBJECT
Direct Subclasses:
--------------------------------------------------------------------------------
SLOTS : FLD DEF PRP ACC STO MCH SRC VIS CRT OVRD-MSG SOURCE(S)
foo : MLT STC INH R SHR RCT CMP PRV R NIL A B
Constraint information for slots:
SLOTS : SYM STR INN INA EXA FTA INT FLT
foo : + + + + + + + + RNG:[-oo..+oo] CRD:[0..+oo]
--------------------------------------------------------------------------------
Recognized message-handlers:
init primary in class USER
delete primary in class USER
create primary in class USER
print primary in class USER
direct-modify primary in class USER
message-modify primary in class USER
direct-duplicate primary in class USER
message-duplicate primary in class USER
get-foo primary in class A
get-foo primary in class B
********************************************************************************
================================================================================
CLIPS>
9.3.3.7 Pattern-Match Reactivity Facet
Normally, any change to a slot of an instance will be considered as a change to the instance for
purposes of pattern-matching. However, it is possible to indicate that changes to a slot of an
instance should not cause pattern-matching. The reactive facet specifies that changes to a slot
trigger pattern-matching, and this is the default. The non-reactive facet specifies that changes to
a slot do not affect pattern-matching.
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot foo (pattern-match non-reactive)))
CLIPS>
(defclass B (is-a USER)
(slot foo))
CLIPS>
(defrule Create
?ins<-(object (is-a A | B))
=>
(printout t "Create " (instance-name ?ins) crlf))
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CLIPS>
(defrule Foo-Access
?ins<-(object (is-a A | B) (foo ?))
=>
(printout t "Foo-Access " (instance-name ?ins) crlf))
CLIPS> (make-instance a of A)
[a]
CLIPS> (make-instance b of B)
[b]
CLIPS> (run)
Create [b]
Foo-Access [b]
Create [a]
CLIPS> (send [a] put-foo 1)
1
CLIPS> (send [b] put-foo 1)
1
CLIPS> (run)
Foo-Access [b]
CLIPS>
9.3.3.8 Visibility Facet
Normally, only message-handlers attached to the class in which a slot is defined may directly
access the slot. However, it is possible to allow message-handlers attached to superclasses or
subclasses which inherit the slot to directly access the slot as well. Declaring the visibility facet
to be private specifies that only the message-handlers of the defining class may directly access
the slot, and this is the default. Declaring the visibility facet to be public specifies that the
message-handlers and subclasses that inherit the slot and superclasses may also directly access
the slot.
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot foo (visibility private)))
CLIPS>
(defclass B (is-a A))
CLIPS>
(defmessage-handler B get-foo ()
?self:foo)
[MSGFUN6] Private slot foo of class A cannot be accessed directly by handlers
attached to class B
[PRCCODE3] Undefined variable self:foo referenced in message-handler.
ERROR:
(defmessage-handler MAIN::B get-foo
()
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?self:foo
)
CLIPS>
9.3.3.9 Create-Accessor Facet
The create-accessor facet instructs CLIPS to automatically create explicit message-handlers for
reading and/or writing a slot. By default, implicit slot-accessor message-handlers are created for
every slot. While these message-handlers are real message-handlers and can be manipulated as
such, they have no pretty-print form and cannot be directly modified by the user.
If the value ?NONE is specified for the facet, no message-handlers are created.
If the value read is specified for the facet, CLIPS creates the following message-handler:
(defmessage-handler <class> get-<slot-name> primary ()
?self:<slot-name>)
If the value write is specified for the facet, CLIPS creates the following message-handler for
single-field slots:
(defmessage-handler <class> put-<slot-name> primary (?value)
(bind ?self:<slot-name> ?value)
or the following message-handler for multifield slots:
(defmessage-handler <class> put-<slot-name> primary ($?value)
(bind ?self:<slot-name> ?value)
If the value read-write is specified for the facet, both the get- and one of the
put- message-handlers are created.
If accessors are required that do not use static slot references (see sections 9.4.2, 9.6.3 and 9.6.4),
then user must define them explicitly with the defmessage-handler construct.
The access facet affects the default value for the create-accessor facet. If the access facet is
read-write, then the default value for the create-accessor facet is read-write. If the access facet
is read-only, then the default value is read. If the access facet is initialize-only, then the default
is ?NONE.
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Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot foo (create-accessor write))
(slot bar (create-accessor read))
CLIPS> (make-instance a of A (foo 36))
[a]
CLIPS> (make-instance b of A (bar 45))
[MSGFUN1] No applicable primary message-handlers found for put-bar.
FALSE
CLIPS>
9.3.3.10 Override-Message Facet
There are several COOL support functions that set slots via use of message-passing, e.g.,
make-instance, initialize-instance, message-modify-instance and
message-duplicate-instance. By default, all these functions attempt to set a slot with the
message called put-<slot-name>. However, if the user has elected not to use standard
slot-accessors and wishes these functions to be able to perform slot-overrides, then the
override-message facet can be used to indicate what message to send instead.
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot special (override-message special-put)))
CLIPS>
(defmessage-handler A special-put primary (?value)
(bind ?self:special ?value))
CLIPS> (watch messages)
CLIPS> (make-instance a of A (special 65))
MSG >> create ED:1 (<Instance-a>)
MSG << create ED:1 (<Instance-a>)
MSG >> special-put ED:1 (<Instance-a> 65)
MSG << special-put ED:1 (<Instance-a> 65)
MSG >> init ED:1 (<Instance-a>)
MSG << init ED:1 (<Instance-a>)
[a]
CLIPS> (unwatch messages)
CLIPS>
9.3.3.11 Constraint Facets
The syntax and functionality of single and multifield constraint facets (attributes) are described
in detail in Section 11. Static and dynamic constraint checking for classes and their instances is
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supported. Static checking is performed when constructs or commands that specify slot
information are being parsed. Object patterns used on the LHS of a rule are also checked to
determine if constraint conflicts exist among variables used in more that one slot. Errors for
inappropriate values are immediately signaled. Static checking is enabled by default. This
behavior can be changed using the set-static-constraint-checking function. Dynamic checking
is also supported. If dynamic checking is enabled, then new instances have their values checked
whenever they are set (e.g. initialization, slot-overrides, and put- access). This dynamic checking
is disabled by default. This behavior can be changed using the
set-dynamic-constraint-checking function. If an violation occurs when dynamic checking is
being performed, then execution will be halted.
Regardless of whether static or dynamic checking is enabled, multifield values can never be
stored in single-field slots. Single-field values are converted to a multifield value of length one
when storing in a multifield slot. In addition, the evaluation of a function that has no return value
is always illegal as a slot value.
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(multislot foo (type SYMBOL)
(cardinality 2 3)))
CLIPS> (make-instance a of A (foo 45))
[a]
CLIPS> (set-dynamic-constraint-checking TRUE)
FALSE
CLIPS> (make-instance a of A (foo red 5.0))
[CSTRNCHK1] (red 5.0) for slot foo of instance [a] found in put-foo primary in
class A does not match the allowed types.
[PRCCODE4] Execution halted during the actions of message-handler put-foo primary
in class A
FALSE
CLIPS> (make-instance a of A (foo red))
[CSTRNCHK1] (red) for slot foo of instance [a] found in put-foo primary in class A
does not satisfy the cardinality restrictions.
[PRCCODE4] Execution halted during the actions of message-handler put-foo primary
in class A
FALSE
CLIPS>
9.3.4 Message-handler Documentation
COOL allows the user to forward declare the message-handlers for a class within the defclass
statement. These declarations are for documentation only and are ignored by CLIPS. The
defmessage-handler construct must be used to actually add message-handlers to a class.
Message-handlers can later be added which are not documented in the defclass.
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Example
CLIPS> (clear)
CLIPS>
(defclass rectangle (is-a USER)
(slot side-a (default 1))
(slot side-b (default 1))
(message-handler find-area))
CLIPS>
(defmessage-handler rectangle find-area ()
(* ?self:side-a ?self:side-b))
CLIPS>
(defmessage-handler rectangle print-area ()
(printout t (send ?self find-area) crlf))
CLIPS>
9.4 Defmessage-handler Construct
Objects are manipulated by sending them messages via the function send. The result of a
message is a useful return-value or side-effect. A defmessage-handler is a construct for
specifying the behavior of a class of objects in response to a particular message. The
implementation of a message is made up of pieces of procedural code called message-handlers
(or handlers for short). Each class in the class precedence list of an object’s class can have
handlers for a message. In this way, the object’s class and all its superclasses share the labor of
handling the message. Each class’s handlers handle the part of the message that is appropriate to
that class. Within a class, the handlers for a particular message can be further subdivided into
four types or categories: primary, before, after and around. The intended purposes of each
type are summarized in the chart below:
Type
Role for the Class
primary
Performs the majority of the work for the message
before
Does auxiliary work for a message before the primary handler executes
after
Does auxiliary work for a message after the primary handler executes
around
Sets up an environment for the execution of the rest of the handlers
Before and after handlers are for side-effects only; their return values are always ignored. Before
handlers execute before the primary ones, and after message-handlers execute after the primary
ones. The return value of a message is generally given by the primary message-handlers, but
around handlers can also return a value. Around message-handlers allow the user to wrap code
around the rest of the handlers. They begin execution before the other handlers and pick up again
after all the other message-handlers have finished.
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A primary handler provides the part of the message implementation which is most specific to an
object, and thus the primary handler attached to the class closest to the immediate class of the
object overrides other primary handlers. Before and after handlers provide the ability to pick up
behavior from classes that are more general than the immediate class of the object, thus the
message implementation uses all handlers of this type from all the classes of an object. When
only the roles of the handlers specify which handlers get executed and in what order, the
message is said to be declaratively implemented. However, some message implementations may
not fit this model well. For example, the results of more than one primary handler may be
needed. In cases like this, the handlers themselves must take part in deciding which handlers get
executed and in what order. This is called the imperative technique. Around handlers provide
imperative control over all other types of handlers except more specific around handlers. Around
handlers can change the environment in which other handlers execute and modify the return
value for the entire message. A message implementation should use the declarative technique if
at all possible because this allows the handlers to be more independent and modular.
A defmessage-handler is comprised of seven elements: 1) a class name to which to attach the
handler (the class must have been previously defined), 2) a message name to which the handler
will respond, 3) an optional type (the default is primary), 4) an optional comment, 5) a list of
parameters that will be passed to the handler during execution, 6) an optional wildcard parameter
and 7) a series of expressions which are executed in order when the handler is called. The
return-value of a message-handler is the evaluation of the last expression in the body.
Syntax
Defaults are in bold italics.
(defmessage-handler <class-name> <message-name>
[<handler-type>] [<comment>]
(<parameter>* [<wildcard-parameter>])
<action>*)
<handler-type> ::= around | before |
primary
| after
<parameter> ::= <single-field-variable>
<wildcard-parameter> ::= <multifield-variable>
Message-handlers are uniquely identified by class, name and type. Message-handlers are never
called directly. When the user sends a message to an object, CLIPS selects and orders the
applicable message-handlers attached to the object’s class(es) and then executes them. This
process is termed the message dispatch.
Example
CLIPS> (clear)
CLIPS> (defclass A (is-a USER))
CLIPS>
(defmessage-handler A delete before ()
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(printout t "Deleting an instance of the class A..." crlf))
CLIPS>
(defmessage-handler USER delete after ()
(printout t "System completed deletion of an instance."
crlf))
CLIPS> (watch instances)
CLIPS> (make-instance a of A)
==> instance [a] of A
[a]
CLIPS> (send [a] delete)
Deleting an instance of the class A...
<== instance [a] of A
System completed deletion of an instance.
TRUE
CLIPS> (unwatch instances)
CLIPS>
9.4.1 Message-handler Parameters
A message-handler may accept exactly or at least a specified number of arguments, depending
on whether a wildcard parameter is used or not. The regular parameters specify the minimum
number of arguments that must be passed to the handler. Each of these parameters may be
referenced like a normal single-field variable within the actions of the handler. If a wildcard
parameter is present, the handler may be passed any number of arguments greater than or equal
to the minimum. If no wildcard parameter is present, then the handler must be passed exactly the
number of arguments specified by the regular parameters. All arguments to a handler that do not
correspond to a regular parameter are grouped into a multifield value that can be referenced by
the wildcard parameter. The standard CLIPS multifield functions, such as length$ and expand$,
can be applied to the wildcard parameter.
Handler parameters have no bearing on the applicability of a handler to a particular message (see
section 9.5.1). However, if the number of arguments is inappropriate, a message execution error
(see section 9.5.4) will be generated when the handler is called. Thus, the number of arguments
accepted should be consistent for all message-handlers applicable to a particular message.
Example
CLIPS> (clear)
CLIPS>
(defclass CAR (is-a USER)
(slot front-seat)
(multislot trunk)
(slot trunk-count))
CLIPS>
(defmessage-handler CAR put-items-in-car (?item $?rest)
(bind ?self:front-seat ?item)
(bind ?self:trunk ?rest)
(bind ?self:trunk-count (length$ ?rest)))
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CLIPS> (make-instance Pinto of CAR)
[Pinto]
CLIPS> (send [Pinto] put-items-in-car bag-of-groceries
tire suitcase)
2
CLIPS> (send [Pinto] print)
[Pinto] of CAR
(front-seat bag-of-groceries)
(trunk tire suitcase)
(trunk-count 2)
CLIPS>
9.4.1.1 Active Instance Parameter
The term active instance refers to an instance that is responding to a message. All
message-handlers have an implicit parameter called ?self which binds the active instance for a
message. This parameter name is reserved and cannot be explicitly listed in the
message-handler’s parameters, nor can it be rebound within the body of a message-handler.
Example
CLIPS> (clear)
CLIPS> (defclass A (is-a USER))
CLIPS> (make-instance a of A)
[a]
CLIPS>
(defmessage-handler A print-args (?a ?b $?c)
(printout t (instance-name ?self) " " ?a " " ?b
" and " (length$ ?c) " extras: " ?c crlf))
CLIPS> (send [a] print-args 1 2)
[a] 1 2 and 0 extras: ()
CLIPS> (send [a] print-args a b c d)
[a] a b and 2 extras: (c d)
CLIPS>
9.4.2 Message-handler Actions
The body of a message-handler is a sequence of expressions that are executed in order when the
handler is called. The return value of the message-handler is the result of the evaluation of the
last expression in the body.
Handler actions may directly manipulate slots of the active instance. Normally, slots can only be
manipulated by sending the object slot-accessor messages (see sections 9.3.3.9 and 9.4.3).
However, handlers are considered part of the encapsulation (see section 2.6.2) of an object, and
thus can directly view and change the slots of the object. There are several functions which
operate implicitly on the active instance (without the use of messages) and can only be called
from within a message-handler. These functions are discussed in section 12.16.
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A shorthand notation is provided for accessing slots of the active instance from within a
message-handler.
Syntax
?self:<slot-name>
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot foo (default 1))
(slot bar (default 2)))
CLIPS>
(defmessage-handler A print-all-slots ()
(printout t ?self:foo " " ?self:bar crlf))
CLIPS> (make-instance a of A)
[a]
CLIPS> (send [a] print-all-slots)
1 2
CLIPS>
The bind function can also take advantage of this shorthand notation to set the value of a slot.
Syntax
(bind ?self:<slot-name> <value>*)
Example
CLIPS>
(defmessage-handler A set-foo (?value)
(bind ?self:foo ?value))
CLIPS> (send [a] set-foo 34)
34
CLIPS>
Direct slot accesses are statically bound to the appropriate slot in the defclass when the
message-handler is defined. Care must be taken when these direct slot accesses can be executed
as the result of a message sent to an instance of a subclass of the class to which the
message-handler is attached. If the subclass has redefined the slot, the direct slot access
contained in the message-handler attached to the superclass will fail. That message-handler
accesses the slot in the superclass, not the subclass.
Example
CLIPS> (clear)
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CLIPS>
(defclass A (is-a USER)
(slot foo (create-accessor read)))
CLIPS>
(defclass B (is-a A)
(slot foo (create-accessor ?NONE)))
CLIPS> (make-instance b of B)
[b]
CLIPS> (send [b] get-foo)
[MSGPASS3] Static reference to slot foo of class A does not apply to [b] of B
[PRCCODE4] Execution halted during the actions of message-handler get-foo primary
in class A
FALSE
CLIPS>
In order for direct slot accesses in a superclass message-handler to apply to new versions of the
slot in subclasses, the dynamic-put and dynamic-get (see sections 12.16.4.10 and 12.16.4.11)
must be used. However, the subclass slot must have public visibility for this to work (see section
9.3.3.8).
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot foo (create-accessor ?NONE)))
CLIPS>
(defmessage-handler A get-foo ()
(dynamic-get foo))
CLIPS>
(defclass B (is-a A)
(role concrete)
(slot foo (visibility public)))
CLIPS> (make-instance b of B)
[b]
CLIPS> (send [b] get-foo)
nil
CLIPS>
9.4.3 Daemons
Daemons are pieces of code which execute implicitly whenever some basic action is taken upon
an instance, such as initialization, deletion, or reading and writing of slots. All these basic actions
are implemented with primary handlers attached to the class of the instance. Daemons may be
easily implemented by defining other types of message-handlers, such as before or after, which
will recognize the same messages. These pieces of code will then be executed whenever the
basic actions are performed on the instance.
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Example
CLIPS> (clear)
CLIPS> (defclass A (is-a USER))
CLIPS>
(defmessage-handler A init before ()
(printout t "Initializing a new instance of class A..."
crlf))
CLIPS> (make-instance a of A)
Initializing a new instance of class A...
[a]
CLIPS>
9.4.4 Predefined System Message-handlers
CLIPS defines eight primary message-handlers that are attached to the class USER. These
handlers cannot be deleted or modified.
9.4.4.1 Instance Initialization
Syntax
(defmessage-handler USER init primary ())
This handler is responsible for initializing instances with class default values after creation. The
make-instance and initialize-instance functions send the init message to an instance (see
sections 9.6.1 and 9.6.2); the user should never send this message directly. This handler is
implemented using the init-slots function (see section 12.13). User-defined init handlers should
not prevent the system message-handler from responding to an init message (see section 9.5.3).
Example
CLIPS> (clear)
CLIPS>
(defclass CAR (is-a USER)
(slot price (default 75000))
(slot model (default Corniche)))
CLIPS> (watch messages)
CLIPS> (watch message-handlers)
CLIPS> (make-instance Rolls-Royce of CAR)
MSG >> create ED:1 (<Instance-Rolls-Royce>)
HND >> create primary in class USER
ED:1 (<Instance-Rolls-Royce>)
HND << create primary in class USER
ED:1 (<Instance-Rolls-Royce>)
MSG << create ED:1 (<Instance-Rolls-Royce>)
MSG >> init ED:1 (<Instance-Rolls-Royce>)
HND >> init primary in class USER
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ED:1 (<Instance-Rolls-Royce>)
HND << init primary in class USER
ED:1 (<Instance-Rolls-Royce>)
MSG << init ED:1 (<Instance-Rolls-Royce>)
[Rolls-Royce]
CLIPS>
9.4.4.2 Instance Deletion
Syntax
(defmessage-handler USER delete primary ())
This handler is responsible for deleting an instance from the system. The user must directly send
a delete message to an instance. User-defined delete message-handlers should not prevent the
system message-handler from responding to a delete message (see section 9.5.3). The handler
returns the symbol TRUE if the instance was successfully deleted, otherwise it returns the
symbol FALSE.
Example
CLIPS> (send [Rolls-Royce] delete)
MSG >> delete ED:1 (<Instance-Rolls-Royce>)
HND >> delete primary in class USER
ED:1 (<Instance-Rolls-Royce>)
HND << delete primary in class USER
ED:1 (<Stale Instance-Rolls-Royce>)
MSG << delete ED:1 (<Stale Instance-Rolls-Royce>)
TRUE
CLIPS>
9.4.4.3 Instance Display
Syntax
(defmessage-handler USER print primary ())
This handler prints out slots and their values for an instance.
Example
CLIPS> (make-instance Rolls-Royce of CAR)
MSG >> create ED:1 (<Instance-Rolls-Royce>)
HND >> create primary in class USER
ED:1 (<Instance-Rolls-Royce>)
HND << create primary in class USER
ED:1 (<Instance-Rolls-Royce>)
MSG << create ED:1 (<Instance-Rolls-Royce>)
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MSG >> init ED:1 (<Instance-Rolls-Royce>)
HND >> init primary in class USER
ED:1 (<Instance-Rolls-Royce>)
HND << init primary in class USER
ED:1 (<Instance-Rolls-Royce>)
MSG << init ED:1 (<Instance-Rolls-Royce>)
[Rolls-Royce]
CLIPS> (send [Rolls-Royce] print)
MSG >> print ED:1 (<Instance-Rolls-Royce>)
HND >> print primary in class USER
ED:1 (<Instance-Rolls-Royce>)
[Rolls-Royce] of CAR
(price 75000)
(model Corniche)
HND << print primary in class USER
ED:1 (<Instance-Rolls-Royce>)
MSG << print ED:1 (<Instance-Rolls-Royce>)
CLIPS> (unwatch messages)
CLIPS. (unwatch message-handlers)
CLIPS>
9.4.4.4 Directly Modifying an Instance
Syntax
(defmessage-handler USER direct-modify primary
(?slot-override-expressions))
This handler modifies the slots of an instance directly rather than using put- override messages to
place the slot values. The slot-override expressions are passed as an EXTERNAL_ADDRESS
data object to the direct-modify handler. This message is used by the functions modify-instance
and active-modify-instance.
Example
The following around message-handler could be used to insure that all modify message
slot-overrides are handled using put- messages.
(defmessage-handler USER direct-modify around
(?overrides)
(send ?self message-modify ?overrides))
9.4.4.5 Modifying an Instance using Messages
Syntax
(defmessage-handler USER message-modify primary
(?slot-override-expressions)
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This handler modifies the slots of an instance using put- messages for each slot update. The
slot-override expressions are passed as an EXTERNAL_ADDRESS data object to the
message-modify handler. This message is used by the functions message-modify-instance and
active-message-modify-instance.
9.4.4.6 Directly Duplicating an Instance
Syntax
(defmessage-handler USER direct-duplicate primary
(?new-instance-name ?slot-override-expressions))
This handler duplicates an instance without using put- messages to assign the slot-overrides. Slot
values from the original instance and slot overrides are directly copied. If the name of the new
instance created matches a currently existing instance-name, then the currently existing instance
is deleted without use of a message. The slot-override expressions are passed as an
EXTERNAL_ADDRESS data object to the direct-duplicate handler. This message is used by the
functions duplicate-instance and active-duplicate-instance.
Example
The following around message-handler could be used to insure that all duplicate message
slot-overrides are handled using put- messages.
(defmessage-handler USER direct-duplicate around
(?new-name ?overrides)
(send ?self message-duplicate ?new-name ?overrides))
9.4.4.7 Duplicating an Instance using Messages
Syntax
(defmessage-handler USER message-duplicate primary
(?new-instance-name ?slot-override-expressions)
This handler duplicates an instance using messages. Slot values from the original instance and
slot overrides are copied using put- and get- messages. If the name of the new instance created
matches a currently existing instance-name, then the currently existing instance is deleted using a
delete message. After creation, the new instance is sent a create message and then an init
message. The slot-override expressions are passed as an EXTERNAL_ADDRESS data object to
the message-duplicate handler. This message is used by the functions
message-duplicate-instance and active-message-duplicate-instance.
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9.4.4.8 Instance Creation
Syntax
(defmessage-handler USER create primary ())
This handler is called after an instance is created, but before any slot initialization has occurred.
The newly created instance is sent a create message. This handler performs no actions—It is
provided so that instance creation can be detected by user-defined message-handlers. The
handler returns the symbol TRUE if the instance was successfully created, otherwise it returns
the symbol FALSE.
9.5 Message Dispatch
When a message is sent to an object using the send function, CLIPS examines the class
precedence list of the active instance’s class to determine a complete set of message-handlers
which are applicable to the message. CLIPS uses the roles (around, before, primary or after) and
specificity of these message-handlers to establish an ordering and then executes them. A handler
that is attached to a subclass of another message-handler’s class is said to be more specific. This
entire process is referred to as the message dispatch. Following is a flow diagram summary:
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The solid arrows indicate automatic control transfer by the message dispatch system. The dashed
arrows indicate control transfer that can only be accomplished by the use or lack of the use of
call-next-handler (or override-next-handler).
DONE: Return control and values to caller.
START: Input is a list of applicable message-handlers.
AROUND STEP: Are there any uncalled around handlers?
YES: Call the most specific uncalled around handler.
If the body uses call-next-handler, repeat this step.
Else go to DONE.
When body returns, return its values to caller.
NO: Proceed to BEFORE STEP.
BEFORE STEP: Are there any uncalled before handlers?
YES: Call the most specific uncalled before handler.
When body returns, repeat this step.
NO: Proceed to PRIMARY STEP
AFTER STEP: Are there any uncalled after handlers?
YES: Call the least specific uncalled after handler.
When body returns, repeat this step.
NO: Proceed to DONE.
PRIMARY STEP: Are there any uncalled primary handlers?
YES: Call the most specific uncalled primary handler.
If the body uses call-next-handler, repeat this step.
When body returns, return its values to caller.
NO: Proceed to AFTER STEP.
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9.5.1 Applicability of Message-handlers
A message-handler is applicable to a message if its name matches the message, and it is attached
to a class which is in the class precedence list of the class of the instance receiving the message.
9.5.2 Message-handler Precedence
The set of all applicable message-handlers are sorted into four groups according to role, and
these four groups are further sorted by class specificity. The around, before and primary handlers
are ordered from most specific to most general, whereas after handlers are ordered from most
general to most specific.
The order of execution is as follows: 1) around handlers begin execution from most specific to
most general (each around handler must explicitly allow execution of other handlers), 2) before
handlers execute (one after the other) from most specific to most general 3) primary handlers
begin execution from most specific to most general (more specific primary handlers must
explicitly allow execution of more general ones), 4) primary handlers finish execution from most
general to most specific, 5) after handlers execute (one after the other) from most general to most
specific and 6) around handlers finish execution from most general to most specific.
There must be at least one applicable primary handler for a message, or a message execution
error will be generated (see section 9.5.4).
9.5.3 Shadowed Message-handlers
When one handler must be called by another handler in order to be executed, the first handler is
said to be shadowed by the second. An around handler shadows all handlers except more
specific around handlers. A primary handler shadows all more general primary handlers.
Messages should be implemented using the declarative technique, if possible. Only the handler
roles will dictate which handlers get executed; only before and after handlers and the most
specific primary handler are used. This allows each handler for a message to be completely
independent of the other message-handlers. However, if around handlers or shadowed primary
handlers are necessary, then the handlers must explicitly take part in the message dispatch by
calling other handlers they are shadowing. This is called the imperative technique. The functions
call-next-handler and override-next-handler (see section 12.16.2) allow a handler to execute
the handler it is shadowing. A handler can call the same shadowed handler multiple times.
Example
(defmessage-handler USER my-message around ()
(call-next-handler))
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(defmessage-handler USER my-message before ())
(defmessage-handler USER my-message ()
(call-next-handler))
(defmessage-handler USER my-message after ())
(defmessage-handler OBJECT my-message around ()
(call-next-handler))
(defmessage-handler OBJECT my-message before ())
(defmessage-handler OBJECT my-message ())
(defmessage-handler OBJECT my-message after ())
For a message sent to an instance of a class which inherits from USER, the following diagram
illustrates the order of execution for the handlers attached to the classes USER and OBJECT.
The brackets indicate where a particular handler begins and ends execution. Handlers enclosed
within a bracket are shadowed.
9.5.4 Message Execution Errors
If an error occurs at any time during the execution of a message-handler, any currently executing
handlers will be aborted, any handlers which have not yet started execution will be ignored, and
the send function will return the symbol FALSE.
A lack of applicable of primary message-handlers and a handler being called with the wrong
number of arguments are common message execution errors.
USER around begin
USER around end
OBJECT around begin
OBJECT around end
USER before
USER after
OBJECT before
OBJECT after
USER primary begin
USER primary end
OBJECT primary
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9.5.5 Message Return Value
The return value of call to the send function is the return value of the most specific around
handler, or the most specific primary handler if there are no around handlers. The return value of
a handler is the result of the evaluation of the last action in the handler.
The return values of the before and after handlers are ignored; they are for side-effects only. An
around handler can choose to ignore or capture the return value of the next most specific around
or primary handler. A primary handler can choose to ignore or capture the return value of a more
general primary handler.
9.6 Manipulating Instances
Objects are manipulated by sending them messages. This is achieved by using the send function,
which takes as arguments the destination object for the message, the message itself and any
arguments which are to be passed to handlers.
Syntax
(send <object-expression>
<message-name-expression> <expression>*)
Section 2.4.2 explains object references. The return value of send is the result of the message as
explained in section 9.5.5.
The slots of an object may be read or set directly only within the body of a message-handler that
is executing on behalf of a message that was sent to that object. This is how COOL implements
the notion of encapsulation (see Section 2.6.2). Any action performed on an object by an external
source, such as a rule or function, must be done with messages. There are two major exceptions:
1) objects which are not instances of user-defined classes (floating-point and integer numbers,
symbols, strings, multifield values, fact-addresses and external-addresses) can be manipulated in
the standard non-OOP manner of previous versions of CLIPS as well and 2) creation and
initialization of an instance of a user-defined class are performed via the function
make-instance.
9.6.1 Creating Instances
Like facts, instances of user-defined classes must be explicitly created by the user. Likewise, all
instances are deleted during the reset command, and they can be loaded and saved similarly to
facts. All operations involving instances require message-passing using the send function except
for creation, since the object does not yet exist. A function called make-instance is used to
create and initialize a new instance. This function implicitly sends first a create message and then
an initialization message to the new object after allocation. The user can customize instance
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initialization with daemons. make-instance also allows slot-overrides to change any predefined
initialization for a particular instance. make-instance automatically delays all object
pattern-matching activities for rules until all slot overrides have been processed. The function
active-make-instance can be used if delayed pattern-matching is not desired.
active-make-instance remembers the current state of delayed pattern-matching, explicitly turns
delay on, and then restores it to its previous state once all slot overrides have been processed.
Syntax
(make-instance <instance-definition>)
(active-make-instance <instance-definition>)
<instance-definition> ::= [<instance-name-expression>] of
<class-name-expression>
<slot-override>*
<slot-override> ::= (<slot-name-expression>
<expression>*)
The return value of make-instance is the name of the new instance on success or the symbol
FALSE on failure. The evaluation of <instance-name-expression> can either be an
instance-name or a symbol. If <instance-name-expression> is not specified, then the function
gensym* will be called to generate the instance-name.
The make-instance function performs the following steps in order:
1) If an instance of the specified name already exists, that instance receives a delete message,
e.g. (send <instance-name> delete). If this fails for any reason, the new instance creation is
aborted. Normally, the handler attached to class USER will respond to this message (see
section 9.4.5.2).
2) A new and uninitialized instance of the specified class is created with the specified name.
3) The new instance receives the create message, e.g. (send <instance-name> create).
Normally, the handler attached to class USER will respond to this message (see section
9.4.4.8), although it performs no actions.
4) All slot-overrides are immediately evaluated and placed via put- messages (see section
9.3.3.10), e.g. (send <instance-name> put-<slot-name> <expression>*). If there are any
errors, the new instance is deleted.
5) The new instance receives the init message, e.g. (send <instance-name> init). Normally, the
handler attached to class USER will respond to this message (see section 9.4.4.1). This
handler calls the init-slots function (see section 12.16.4.1). This function uses defaults from
the class definition (if any) for any slots which do not have slot-overrides. The class defaults
are placed directly without the use of messages. If there are any errors, the new instance is
deleted.
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Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot x (default 34))
(slot y (default abc)))
CLIPS>
(defmessage-handler A put-x before (?value)
(printout t "Slot x set with message." crlf))
CLIPS>
(defmessage-handler A delete after ()
(printout t "Old instance deleted." crlf))
CLIPS> (make-instance a of A)
[a]
CLIPS> (send [a] print)
[a] of A
(x 34)
(y abc)
CLIPS> (make-instance [a] of A (x 65))
Old instance deleted.
Slot x set with message.
[a]
CLIPS> (send [a] print)
a of A
(x 65)
(y abc)
CLIPS> (send [a] delete)
Old instance deleted.
TRUE
CLIPS>
9.6.1.1 Definstances Construct
Similar to deffacts, the definstances construct allows the specification of instances which will be
created every time the reset command is executed. On every reset all current instances receive a
delete message, and the equivalent of a make-instance function call is made for every instance
specified in definstances constructs.
Syntax
(definstances <definstances-name> [active] [<comment>]
<instance-template>*)
<instance-template> ::= (<instance-definition>)
A definstances cannot use classes that have not been previously defined. The instances of a
definstances are created in order, and if any individual creation fails, the remainder of the
definstances will be aborted. Normally, definstances just use the make-instance function (which
means delayed Rete activity) to create the instances. However, if this is not desired, then the
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active keyword can be specified after the definstances name so that the active-make-instance
function will be used.
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot x (default 1)))
CLIPS>
(definstances A-OBJECTS
(a1 of A)
(of A (x 65)))
CLIPS> (watch instances)
CLIPS> (reset)
<== instance [initial-object] of INITIAL-OBJECT
==> instance [initial-object] of INITIAL-OBJECT
==> instance [a1] of A
==> instance [gen1] of A
CLIPS> (reset)
<== instance [initial-object] of INITIAL-OBJECT
<== instance [a1] of A
<== instance [gen1] of A
==> instance [initial-object] of INITIAL-OBJECT
==> instance [a1] of A
==> instance [gen2] of A
CLIPS> (unwatch instances)
CLIPS>
Upon startup and after a clear command, CLIPS automatically constructs the following
definstances.
(definstances initial-object
(initial-object of INITIAL-OBJECT))
The class INITIAL-OBJECT is a predefined system class that is a direct subclass of USER.
(defclass INITIAL-OBJECT
(is-a USER)
(role concrete)
(pattern-match reactive))
The initial-object definstances and the INITIAL-OBJECT class are only defined if both the
object system and defrules are enabled (see section 2 of the Advanced Programming Guide). The
INITIAL-OBJECT class cannot be deleted, but the initial-object definstances can. See section
5.4.9 for details on default patterns which pattern-match against the initial-object instance.
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9.6.2 Reinitializing Existing Instances
The initialize-instance function provides the ability to reinitialize an existing instance with class
defaults and new slot-overrides. The return value of initialize-instance is the name of the
instance on success or the symbol FALSE on failure. The evaluation of
<instance-name-expression> can either be an instance-name, instance-address or a symbol.
initialize-instance automatically delays all object pattern-matching activities for rules until all
slot overrides have been processed. The function active-initialize-instance can be used if
delayed pattern-matching is not desired.
Syntax
(initialize-instance <instance-name-expression>
<slot-override>*)
The initialize-instance function performs the following steps in order:
1) All slot-overrides are immediately evaluated and placed via put- messages (see section
9.3.3.10), e.g. (send <instance-name> put-<slot-name> <expression>*).
2) The instance receives the init message, e.g. (send <instance-name> init). Normally, the
handler attached to class USER will respond to this message (see section 9.4.5.1). This
handler calls the init-slots function (see section 12.16.4.1). This function uses defaults from
the class definition (if any) for any slots that do not have slot-overrides. The class defaults
are placed directly without the use of messages.
If no slot-override or class default specifies the value of a slot, that value will remain the same.
Empty class default values allow initialize-instance to clear a slot.
If an error occurs, the instance will not be deleted, but the slot values may be in an inconsistent
state.
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot x (default 34))
(slot y (default abc))
(slot z))
CLIPS> (make-instance a of A (y 100))
[a]
CLIPS> (send [a] print)
[a] of A
(x 34)
(y 100)
(z nil)
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CLIPS> (send [a] put-x 65)
65
CLIPS> (send [a] put-y abc)
abc
CLIPS> (send [a] put-z "Hello world.")
“Hello world.”
CLIPS> (send [a] print)
[a] of A
(x 65)
(y abc)
(z "Hello world.")
CLIPS> (initialize-instance a)
[a]
CLIPS> (send [a] print)
a of A
(x 34)
(y abc)
(z nil)
CLIPS>
9.6.3 Reading Slots
Sources external to an object, such as a rule or deffunction, can read an object’s slots only by
sending the object a message. Message-handlers executing on the behalf of an object can either
use messages or direct access to read the object’s slots (see section 9.4.2). Several functions also
exist which operate implicitly on the active instance for a message that can only be called by
message-handlers, such as dynamic-get (see section 12.16.4.10).
Section 12.16 describes ways of testing for the existence of slots and their values.
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot x (default abc)))
CLIPS> (make-instance a of A)
[a]
CLIPS> (sym-cat (send [a] get-x) def)
abcdef
CLIPS>
9.6.4 Setting Slots
Sources external to an object, such as a rule or deffunction, can write an object’s slots only by
sending the object a message. Several functions also exist which operate implicitly on the active
instance for a message that can only be called by message-handlers, such as dynamic-put (see
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section 12.16.4.11). The bind function can also be used to set a slot's value from within a
message-handler (see section 9.4.2).
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot x (default abc)))
CLIPS> (make-instance a of A)
[a]
CLIPS> (send [a] put-x "New value.")
“New value.”
CLIPS>
9.6.5 Deleting Instances
Sending the delete message to an instance removes it from the system. Within a
message-handler, the delete-instance function (see section 12.16) can be used to delete the
active instance for a message.
Syntax
(send <instance> delete)
9.6.6 Delayed Pattern-Matching When Manipulating Instances
While manipulating instances (either by creating, modifying, or deleting), it is possible to delay
pattern-matching activities for rules until after all of the manipulations have been made. This can
be accomplished using the object-pattern-match-delay function. This function acts identically
to the progn function, however, any actions that could affect object pattern-matching for rules
are delayed until the function is exited. This function’s primary purpose is to provide some
control over performance.
Syntax
(object-pattern-match-delay <action>*)
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER))
CLIPS>
(defrule match-A
(object (is-a A))
=>)
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CLIPS> (make-instance a of A)
[a]
CLIPS> (agenda)
0 match-A: [a]
For a total of 1 activation.
CLIPS> (make-instance b of A)
[b]
CLIPS> (agenda)
0 match-A: [b]
0 match-A: [a]
For a total of 2 activations.
CLIPS>
(object-pattern-match-delay
(make-instance c of A)
(printout t "After c..." crlf)
(agenda)
(make-instance d of A)
(printout t "After d..." crlf)
(agenda))
After c...
0 match-A: [b]
0 match-A: [a]
For a total of 2 activations.
After d...
0 match-A: [b]
0 match-A: [a]
For a total of 2 activations.
CLIPS> (agenda)
0 match-A: [d]
0 match-A: [c]
0 match-A: [b]
0 match-A: [a]
For a total of 4 activations.
CLIPS>
9.6.7 Modifying Instances
Four functions are provided for modifying instances. These functions allow instance slot updates
to be performed in blocks without requiring a series of put- messages. Each of these functions
returns the symbol TRUE if successful, otherwise the symbol FALSE is returned.
9.6.7.1 Directly Modifying an Instance with Delayed Pattern-Matching
The modify-instance function uses the direct-modify message to change the values of the
instance. Object pattern-matching is delayed until all of the slot modifications have been
performed.
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Syntax
(modify-instance <instance> <slot-override>*)
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot foo)
(slot bar))
CLIPS> (make-instance a of A)
[a]
CLIPS> (watch all)
CLIPS> (modify-instance a (foo 0))
MSG >> direct-modify ED:1 (<Instance-a> <Pointer-0019CD5A>)
HND >> direct-modify primary in class USER.
ED:1 (<Instance-a> <Pointer-0019CD5A>)
::= local slot foo in instance a <- 0
HND << direct-modify primary in class USER.
ED:1 (<Instance-a> <Pointer-0019CD5A>)
MSG << direct-modify ED:1 (<Instance-a> <Pointer-0019CD5A>)
TRUE
CLIPS> (unwatch all)
CLIPS>
9.6.7.2 Directly Modifying an Instance with Immediate Pattern-Matching
The active-modify-instance function uses the direct-modify message to change the values of
the instance. Object pattern-matching occurs as slot modifications are being performed.
Syntax
(active-modify-instance <instance> <slot-override>*)
9.6.7.3 Modifying an Instance using Messages with Delayed Pattern-Matching
The message-modify-instance function uses the message-modify message to change the values
of the instance. Object pattern-matching is delayed until all of the slot modifications have been
performed.
Syntax
(message-modify-instance <instance> <slot-override>*)
Example
CLIPS> (clear)
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CLIPS>
(defclass A (is-a USER)
(slot foo)
(slot bar))
CLIPS> (make-instance a of A)
[a]
CLIPS> (watch all)
CLIPS> (message-modify-instance a (bar 4))
MSG >> message-modify ED:1 (<Instance-a> <Pointer-009F04A0>)
HND >> message-modify primary in class USER
ED:1 (<Instance-a> <Pointer-009F04A0>)
MSG >> put-bar ED:2 (<Instance-a> 4)
HND >> put-bar primary in class A
ED:2 (<Instance-a> 4)
::= local slot bar in instance a <- 4
HND << put-bar primary in class A
ED:2 (<Instance-a> 4)
MSG << put-bar ED:2 (<Instance-a> 4)
HND << message-modify primary in class USER
ED:1 (<Instance-a> <Pointer-009F04A0>)
MSG << message-modify ED:1 (<Instance-a> <Pointer-009F04A0>)
TRUE
CLIPS> (unwatch all)
CLIPS>
9.6.7.4 Modifying an Instance using Messages with Immediate Pattern-Matching
The active-message-modify-instance function uses the message-modify message to change the
values of the instance. Object pattern-matching occurs as slot modifications are being performed.
Syntax
(active-message-modify-instance <instance> <slot-override>*)
9.6.8 Duplicating Instances
Four functions are provided for duplicating instances. These functions allow instance duplication
and slot updates to be performed in blocks without requiring a series of put- messages. Each of
these functions return the instance-name of the new duplicated instance if successful, otherwise
the symbol FALSE is returned.
Each of the duplicate functions can optionally specify the name of the instance to which the old
instance will be copied. If the name is not specified, the function will generate the name using
the (gensym*) function. If the target instance already exists, it will be deleted directly or with a
delete message depending on which function was called.
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9.6.8.1 Directly Duplicating an Instance with Delayed Pattern-Matching
The duplicate-instance function uses the direct-duplicate message to change the values of the
instance. Object pattern-matching is delayed until all of the slot modifications have been
performed.
Syntax
(duplicate-instance <instance> [to <instance-name>]
<slot-override>*)
Example
CLIPS> (clear)
CLIPS> (setgen 1)
1
CLIPS>
(defclass A (is-a USER)
(slot foo)
(slot bar))
CLIPS> (make-instance a of A (foo 0) (bar 4))
[a]
CLIPS> (watch all)
CLIPS> (duplicate-instance a)
MSG >> direct-duplicate ED:1 (<Instance-a> [gen1] <Pointer-00000000>)
HND >> direct-duplicate primary in class USER
ED:1 (<Instance-a> [gen1] <Pointer-00000000>)
==> instance [gen1] of A
::= local slot foo in instance gen1 <- 0
::= local slot bar in instance gen1 <- 4
HND << direct-duplicate primary in class USER
ED:1 (<Instance-a> [gen1] <Pointer-00000000>)
MSG << direct-duplicate ED:1 (<Instance-a> [gen1] <Pointer-00000000>)
[gen1]
CLIPS> (unwatch all)
CLIPS>
9.6.8.2 Directly Duplicating an Instance with Immediate Pattern-Matching
The active-duplicate-instance function uses the direct-duplicate message to change the values
of the instance. Object pattern-matching occurs as slot modifications are being performed.
Syntax
(active-duplicate-instance <instance> [to <instance-name>]
<slot-override>*)
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9.6.8.3 Duplicating an Instance using Messages with Delayed Pattern-Matching
The message-duplicate-instance function uses the message-duplicate message to change the
values of the instance. Object pattern-matching is delayed until all of the slot modifications have
been performed.
Syntax
(message-duplicate-instance <instance> [to <instance-name>]
<slot-override>*)
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot foo)
(slot bar))
CLIPS> (make-instance a of A (foo 0) (bar 4))
[a]
CLIPS> (make-instance b of A)
[b]
CLIPS> (watch all)
CLIPS> (message-duplicate-instance a to b (bar 6))
MSG >> message-duplicate ED:1 (<Instance-a> [b] <Pointer-009F04A0>)
HND >> message-duplicate primary in class USER
ED:1 (<Instance-a> [b] <Pointer-009F04A0>)
MSG >> delete ED:2 (<Instance-b>)
HND >> delete primary in class USER
ED:2 (<Instance-b>)
<== instance [b] of A
HND << delete primary in class USER
ED:2 (<Stale Instance-b>)
MSG << delete ED:2 (<Stale Instance-b>)
==> instance [b] of A
MSG >> create ED:2 (<Instance-b>)
HND >> create primary in class USER
ED:2 (<Instance-b>)
HND << create primary in class USER
ED:2 (<Instance-b>)
MSG << create ED:2 (<Instance-b>)
MSG >> put-bar ED:2 (<Instance-b> 6)
HND >> put-bar primary in class A
ED:2 (<Instance-b> 6)
::= local slot bar in instance b <- 6
HND << put-bar primary in class A
ED:2 (<Instance-b> 6)
MSG << put-bar ED:2 (<Instance-b> 6)
MSG >> put-foo ED:2 (<Instance-b> 0)
HND >> put-foo primary in class A
ED:2 (<Instance-b> 0)
::= local slot foo in instance b <- 0
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HND << put-foo primary in class A
ED:2 (<Instance-b> 0)
MSG << put-foo ED:2 (<Instance-b> 0)
MSG >> init ED:2 (<Instance-b>)
HND >> init primary in class USER
ED:2 (<Instance-b>)
HND << init primary in class USER
ED:2 (<Instance-b>)
MSG << init ED:2 (<Instance-b>)
HND << message-duplicate primary in class USER
ED:1 (<Instance-a> [b] <Pointer-009F04A0>)
MSG << message-duplicate ED:1 (<Instance-a> [b] <Pointer-009F04A0>)
[b]
CLIPS> (unwatch all)
CLIPS>
9.6.8.4 Duplicating an Instance using Messages with Immediate Pattern-Matching
The active-message-duplicate-instance function uses the message-duplicate message to change
the values of the instance. Object pattern-matching occurs as slot modifications are being
performed.
Syntax
(active-message-duplicate-instance <instance>
[to <instance-name>]
<slot-override>*)
9.7 Instance-set Queries and Distributed Actions
COOL provides a useful query system for determining and performing actions on sets of
instances of user-defined classes that satisfy user-defined queries. The instance query system in
COOL provides six functions, each of which operate on instance-sets determined by user-defined
criteria:
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Function
Purpose
any-instancep
Determines if one or more instance-sets
satisfy a query
find-instance
Returns the first instance-set that satisfies a
query
find-all-instances
Groups and returns all instance-sets which
satisfy a query
do-for-instance
Performs an action for the first instance-set
which satisfies a query
do-for-all-instances
Performs an action for every instance-set
which satisfies a query as they are found
delayed-do-for-all-instances
Groups all instance-sets which satisfy a query
and then iterates an action over this group
Explanations on how to form instance-set templates, queries and actions immediately follow, for
these definitions are common to all of the query functions. The specific details of each query
function will then be given. The following is a complete example of an instance-set query
function:
Example
For all of the examples in this section, assume that the commands below have already been
entered:
Example
CLIPS>
(defclass PERSON (is-a USER)
(role abstract)
(slot sex (access read-only)
(storage shared))
(slot age (type NUMBER)
CLIPS>
(do-for-all-instances
((?car1 MASERATI BMW) (?car2 ROLLS-ROYCE))
(> ?car1:price (* 1.5 ?car2:price))
(printout t ?car1:name crlf))
[Albert-Maserati]
CLIPS>
Instance-set template
Instance-set query
Instance-set distributed action
Instance-set member variables
Instance-set member class restrictions
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(create-accessor ?NONE)
(visibility public)))
CLIPS>
(defmessage-handler PERSON put-age (?value)
(dynamic-put age ?value))
CLIPS>
(defclass FEMALE (is-a PERSON)
(role abstract)
(slot sex (source composite)
(default female)))
CLIPS>
(defclass MALE (is-a PERSON)
(role abstract)
(slot sex (source composite)
(default male)))
CLIPS>
(defclass GIRL (is-a FEMALE)
(role concrete)
(slot age (source composite)
(default 4)
(range 0.0 17.9)))
CLIPS>
(defclass WOMAN (is-a FEMALE)
(role concrete)
(slot age (source composite)
(default 25)
(range 18.0 100.0)))
CLIPS>
(defclass BOY (is-a MALE)
(role concrete)
(slot age (source composite)
(default 4)
(range 0.0 17.9)))
CLIPS>
(defclass MAN (is-a MALE)
(role concrete)
(slot age (source composite)
(default 25)
(range 18.0 100.0)))
CLIPS>
(definstances PEOPLE
(Man-1 of MAN (age 18))
(Man-2 of MAN (age 60))
(Woman-1 of WOMAN (age 18))
(Woman-2 of WOMAN (age 60))
(Woman-3 of WOMAN)
(Boy-1 of BOY (age 8))
(Boy-2 of BOY)
(Boy-3 of BOY)
(Boy-4 of BOY)
(Girl-1 of GIRL (age 8))
(Girl-2 of GIRL))
CLIPS> (reset)
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CLIPS>
9.7.1 Instance-set Definition
An instance-set is an ordered collection of instances. Each instance-set member is an instance
of a set of classes, called class restrictions, defined by the user. The class restrictions can be
different for each instance-set member. The query functions use instance-set templates to
generate instance-sets. An instance-set template is a set of instance-set member variables and
their associated class restrictions. Instance-set member variables reference the corresponding
members in each instance-set that matches a template. Variables may be used to specify the
classes for the instance-set template, but if the constant names of the classes are specified, the
classes must already be defined. Module specifiers may be included with the class names; the
classes need not be in scope of the current module.
Syntax
<instance-set-template>
::= (<instance-set-member-template>+)
<instance-set-member-template>
::= (<instance-set-member-variable> <class-restrictions>)
<instance-set-member-variable> ::= <single-field-variable>
<class-restrictions> ::= <class-name-expression>+
Example
One instance-set template might be the ordered pairs of boys or men and girls or women.
((?man-or-boy BOY MAN) (?woman-or-girl GIRL WOMAN))
This instance-set template could have been written equivalently:
((?man-or-boy MALE) (?woman-or-girl FEMALE))
Instance-set member variables (e.g. ?man-or-boy) are bound to instance-names.
9.7.2 Instance-set Determination
COOL uses straightforward permutations to generate instance-sets that match an instance-set
template from the actual instances in the system. The rules are as follows:
1) When there is more than one member in an instance-set template, vary the rightmost
members first.
2) When there is more than one class that an instance-set member can be, iterate through the
classes from left to right.
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3) Examine instances of a class in the order that they were defined.
a) Recursively examine instances of subclasses in the order that the subclasses were
defined. If the specified query class was in scope of the current module, then only
subclasses that are also in scope will be examined. Otherwise, only subclasses that are in
scope of the module to which the query class belongs will be examined.
Example
For the instance-set template given in section 9.7.1, thirty instance-sets would be generated in the
following order:
1. [Boy-1] [Girl-1]
2. [Boy-1] [Girl-2]
3. [Boy-1] [Woman-1]
4. [Boy-1] [Woman-2]
5. [Boy-1] [Woman-3]
6. [Boy-2] [Girl-1]
7. [Boy-2] [Girl-2]
8. [Boy-2] [Woman-1]
9. [Boy-2] [Woman-2]
10. [Boy-2] [Woman-3]
11. [Boy-3] [Girl-1]
12. [Boy-3] [Girl-2]
13 [Boy-3] [Woman-1]
14. [Boy-3] [Woman-2]
15. [Boy-3] [Woman-3]
16. [Boy-4] [Girl-1]
17. [Boy-4] [Girl-2]
18. [Boy-4] [Woman-1]
19. [Boy-4] [Woman-2]
20. [Boy-4] [Woman-3]
21. [Man-1] [Girl-1]
22. [Man-1] [Girl-2]
23. [Man-1] [Woman-1]
24. [Man-1] [Woman-2]
25. [Man-1] [Woman-3]
26. [Man-2] [Girl-1]
27. [Man-2] [Girl-2]
28. [Man-2] [Woman-1]
29. [Man-2] [Woman-2]
30. [Man-2] [Woman-3]
Example
Consider the following instance-set template:
((?f1 FEMALE) (?f2 FEMALE))
Twenty-five instance-sets would be generated in the following order:
1. [Girl-1] [Girl-1]
2. [Girl-1] [Girl-2]
3. [Girl-1] [Woman-1]
4. [Girl-1] [Woman-2]
5. [Girl-1] [Woman-3]
6. [Girl-2] [Girl-1]
7. [Girl-2] [Girl-2]
8. [Girl-2] [Woman-1]
9. [Girl-2] [Woman-2]
10.[Girl-2] [Woman-3]
11.[Woman-1] [Girl-1]
12.[Woman-1] [Girl-2]
13.[Woman-1] [Woman-1]
14.[Woman-1] [Woman-2]
15.[Woman-1] [Woman-3]
16.[Woman-2] [Girl-1]
17.[Woman-2] [Girl-2]
18.[Woman-2] [Woman-1]
19.[Woman-2] [Woman-2]
20.[Woman-2] [Woman-3]
21.[Woman-3] [Girl-1]
22.[Woman-3] [Girl-2]
23.[Woman-3] [Woman-1]
24.[Woman-3] [Woman-2]
25.[Woman-3] [Woman-3]
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The instances of class GIRL are examined before the instances of class WOMAN because GIRL
was defined before WOMAN.
9.7.3 Query Definition
A query is a user-defined boolean expression applied to an instance-set to determine if the
instance-set meets further user-defined restrictions. If the evaluation of this expression for an
instance-set is anything but the symbol FALSE, the instance-set is said to satisfy the query.
Syntax
<query> ::= <boolean-expression>
Example
Continuing the previous example, one query might be that the two instances in an ordered pair
have the same age.
(= (send ?man-or-boy get-age) (send ?woman-or-girl get-age))
Within a query, slots of instance-set members can be directly read with a shorthand notation
similar to that used in message-handlers (see section 9.4.2). If message-passing is not explicitly
required for reading a slot (i.e. there are no accessor daemons for reads), then this second method
of slot access should be used, for it gives a significant performance benefit.
Syntax
<instance-set-member-variable>:<slot-name>
Example
The previous example could be rewritten as:
(= ?man-or-boy:age ?woman-or-girl:age)
Since only instance-sets that satisfy a query are of interest, and the query is evaluated for all
possible instance-sets, the query should not have any side-effects.
9.7.4 Distributed Action Definition
A distributed action is a user-defined expression evaluated for each instance-set which satisfies
a query. Unlike queries, distributed actions must use messages to read slots of instance-set
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members. If more than one action is required, use the progn function (see section 12.6.5) to
group them.
Action Syntax
<action> ::= <expression>
Example
Continuing the previous example, one distributed action might be to simply print out the ordered
pair to the screen.
(printout t "(" ?man-or-boy "," ?woman-or-girl ")" crlf)
9.7.5 Scope in Instance-set Query Functions
An instance-set query function can be called from anywhere that a regular function can be called.
If a variable from an outer scope is not masked by an instance-set member variable, then that
variable may be referenced within the query and action. In addition, rebinding variables within
an instance-set function action is allowed. However, attempts to rebind instance-set member
variables will generate errors. Binding variables is not allowed within a query. Instance-set query
functions can be nested.
Example
CLIPS>
(deffunction count-instances (?class)
(bind ?count 0)
(do-for-all-instances ((?ins ?class)) TRUE
(bind ?count (+ ?count 1)))
?count)
CLIPS>
(deffunction count-instances-2 (?class)
(length (find-all-instances ((?ins ?class)) TRUE)))
CLIPS> (count-instances WOMAN)
3
CLIPS> (count-instances-2 BOY)
4
CLIPS>
Instance-set member variables are only in scope within the instance-set query function.
Attempting to use instance-set member variables in an outer scope will generate an error.
Example
CLIPS>
(deffunction last-instance (?class)
(any-instancep ((?ins ?class)) TRUE)
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?ins)
[PRCCODE3] Undefined variable ins referenced in deffunction.
ERROR:
(deffunction MAIN::last-instance
(?class)
(any-instancep ((?ins ?class))
TRUE)
?ins
)
CLIPS>
9.7.6 Errors during Instance-set Query Functions
If an error occurs during an instance-set query function, the function will be immediately
terminated and the return value will be the symbol FALSE.
9.7.7 Halting and Returning Values from Query Functions
The functions break and return are now valid inside the action of the instance-set query
functions do-for-instance, do-for-all-instances and delayed-do-for-all-instances. The return
function is only valid if it is applicable in the outer scope, whereas the break function actually
halts the query.
9.7.8 Instance-set Query Functions
The instance query system in COOL provides six functions. For a given set of instances, all six
query functions will iterate over these instances in the same order (see section 9.7.2). However,
if a particular instance is deleted and recreated, the iteration order will change.
9.7.8.1 Testing if Any Instance-set Satisfies a Query
This function applies a query to each instance-set that matches the template. If an instance-set
satisfies the query, then the function is immediately terminated, and the return value is the
symbol TRUE. Otherwise, the return value is the symbol FALSE.
Syntax
(any-instancep <instance-set-template> <query>)
Example
Are there any men over age 30?
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CLIPS> (any-instancep ((?man MAN)) (> ?man:age 30))
TRUE
CLIPS>
9.7.8.2 Determining the First Instance-set Satisfying a Query
This function applies a query to each instance-set that matches the template. If an instance-set
satisfies the query, then the function is immediately terminated, and the instance-set is returned
in a multifield value. Otherwise, the return value is a zero-length multifield value. Each field of
the multifield value is an instance-name representing an instance-set member.
Syntax
(find-instance <instance-set-template> <query>)
Example
Find the first pair of a man and a woman who have the same age.
CLIPS>
(find-instance ((?m MAN) (?w WOMAN)) (= ?m:age ?w:age))
([Man-1] [Woman-1])
CLIPS>
9.7.8.3 Determining All Instance-sets Satisfying a Query
This function applies a query to each instance-set that matches the template. Each instance-set
that satisfies the query is stored in a multifield value. This multifield value is returned when the
query has been applied to all possible instance-sets. If there are n instances in each instance-set,
and m instance-sets satisfied the query, then the length of the returned multifield value will be n
* m. The first n fields correspond to the first instance-set, and so on. Each field of the multifield
value is an instance-name representing an instance-set member. The multifield value can
consume a large amount of memory due to permutational explosion, so this function should be
used judiciously.
Syntax
(find-all-instances <instance-set-template> <query>)
Example
Find all pairs of a man and a woman who have the same age.
CLIPS>
(find-all-instances ((?m MAN) (?w WOMAN)) (= ?m:age ?w:age))
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([Man-1] [Woman-1] [Man-2] [Woman-2])
CLIPS>
9.7.8.4 Executing an Action for the First Instance-set Satisfying a Query
This function applies a query to each instance-set that matches the template. If an instance-set
satisfies the query, the specified action is executed, and the function is immediately terminated.
The return value is the evaluation of the action. If no instance-set satisfied the query, then the
return value is the symbol FALSE.
Syntax
(do-for-instance <instance-set-template> <query> <action>*)
Example
Print out the first triplet of different people that have the same age. The calls to neq in the query
eliminate the permutations where two or more members of the instance-set are identical.
CLIPS>
(do-for-instance ((?p1 PERSON) (?p2 PERSON) (?p3 PERSON))
(and (= ?p1:age ?p2:age ?p3:age)
(neq ?p1 ?p2)
(neq ?p1 ?p3)
(neq ?p2 ?p3))
(printout t ?p1 " " ?p2 " " ?p3 crlf))
[Girl-2] [Boy-2] [Boy-3]
CLIPS>
9.7.8.5 Executing an Action for All Instance-sets Satisfying a Query
This function applies a query to each instance-set that matches the template. If an instance-set
satisfies the query, the specified action is executed. The return value is the evaluation of the
action for the last instance-set that satisfied the query. If no instance-set satisfied the query, then
the return value is the symbol FALSE.
Syntax
(do-for-all-instances <instance-set-template> <query> <action>*)
Example
Print out all triplets of different people that have the same age. The calls to str-compare limit the
instance-sets that satisfy the query to combinations instead of permutations. Without these
restrictions, two instance-sets that differed only in the order of their members would both satisfy
the query.
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CLIPS>
(do-for-all-instances ((?p1 PERSON) (?p2 PERSON) (?p3 PERSON))
(and (= ?p1:age ?p2:age ?p3:age)
(> (str-compare ?p1 ?p2) 0)
(> (str-compare ?p2 ?p3) 0))
(printout t ?p1 " " ?p2 " " ?p3 crlf))
[Girl-2] [Boy-3] [Boy-2]
[Girl-2] [Boy-4] [Boy-2]
[Girl-2] [Boy-4] [Boy-3]
[Boy-4] [Boy-3] [Boy-2]
CLIPS>
9.7.8.6 Executing a Delayed Action for All Instance-sets
Satisfying a Query
This function is similar to do-for-all-instances except that it groups all instance-sets that satisfy
the query into an intermediary multifield value. If there are no instance-sets which satisfy the
query, then the function returns the symbol FALSE. Otherwise, the specified action is executed
for each instance-set in the multifield value, and the return value is the evaluation of the action
for the last instance-set to satisfy the query. The intermediary multifield value is discarded. This
function can consume large amounts of memory in the same fashion as find-all-instances. This
function should be used in lieu of do-for-all-instances when the action applied to one
instance-set would change the result of the query for another instance-set (unless that is the
desired effect).
Syntax
(delayed-do-for-all-instances <instance-set-template>
<query> <action>*)
Example
Delete all boys with the greatest age. The test in this case is another query function that
determines if there are any older boys than the one currently being examined. The action needs
to be delayed until all boys have been processed, or the greatest age will decrease as the older
boys are deleted.
CLIPS> (watch instances)
CLIPS>
(delayed-do-for-all-instances ((?b1 BOY))
(not (any-instancep ((?b2 BOY))
(> ?b2:age ?b1:age)))
(send ?b1 delete))
<== instance [Boy-1] of BOY
TRUE
CLIPS> (unwatch instances)
CLIPS> (reset)
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CLIPS> (watch instances)
CLIPS>
(do-for-all-instances ((?b1 BOY))
(not (any-instancep ((?b2 BOY))
(> ?b2:age ?b1:age)))
(send ?b1 delete))
<== instance [Boy-1] of BOY
<== instance [Boy-2] of BOY
<== instance [Boy-3] of BOY
<== instance [Boy-4] of BOY
TRUE
CLIPS> (unwatch instances)
CLIPS>
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Section 10:
Defmodule Construct
CLIPS provides support for the modular development and execution of knowledge bases with
the defmodule construct. CLIPS modules allow a set of constructs to be grouped together such
that explicit control can be maintained over restricting the access of the constructs by other
modules. This type of control is similar to global and local scoping used in languages such as C
or Ada (note, however, that the global scoping used by CLIPS is strictly hierarchical and in one
direction only—if module A can see constructs from module B, then it is not possible for module
B to see any of module A’s constructs). By restricting access to deftemplate and defclass
constructs, modules can function as blackboards, permitting only certain facts and instances to be
seen by other modules. Modules are also used by rules to provide execution control.
10.1 Defining Modules
Modules are defined using the defmodule construct.
Syntax
(defmodule <module-name> [<comment>]
<port-specification>*)
<port-specification> ::= (export <port-item>) |
(import <module-name> <port-item>)
<port-item> ::= ?ALL |
?NONE |
<port-construct> ?ALL |
<port-construct> ?NONE |
<port-construct> <construct-name>+
<port-construct> ::= deftemplate | defclass |
defglobal | deffunction |
defgeneric
A defmodule cannot be redefined or even deleted once it is defined (with the exception of the
MAIN module which can be redefined once). The only way to delete a module is with the clear
command. Upon startup and after a clear command, CLIPS automatically constructs the
following defmodule.
(defmodule MAIN)
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All of the predefined system classes (see section 9.2) belong to the MAIN module. However, it is
not necessary to import or export the system classes; they are always in scope. Discounting the
previous exception, the predefined MAIN module does not import or export any constructs.
However, unlike other modules, the MAIN module can be redefined once after startup or a clear
command.
Example
(defmodule FOO
(import BAR ?ALL)
(import YAK deftemplate ?ALL)
(import GOZ defglobal x y z)
(export defgeneric +)
(export defclass ?ALL))
10.2 Specifying a Construct’s Module
The module in which a construct is placed can be specified when the construct is defined. The
deffacts, deftemplate, defrule, deffunction, defgeneric, defclass, and definstances constructs all
specify the module for the construct by including it as part of the name. The module of a
defglobal construct is indicated by specifying the module name after the defglobal keyword. The
module of a defmessage-handler is specified as part of the class specifier. The module of a
defmethod is specified as part of the generic function specifier. For example, the following
constructs would be placed in the DETECTION module.
(defrule DETECTION::Find-Fault
(sensor (name ?name) (value bad))
=>
(assert (fault (name ?name))))
(defglobal DETECTION ?*count* = 0)
(defmessage-handler DETECTION::COMPONENT get-charge ()
(* ?self:flux ?self:flow))
(defmethod DETECTION::+ ((?x STRING) (?y STRING))
(str-cat ?x ?y))
Example
CLIPS> (clear)
CLIPS> (defmodule A)
CLIPS> (defmodule B)
CLIPS> (defrule foo =>)
CLIPS> (defrule A::bar =>)
CLIPS> (list-defrules)
bar
For a total of 1 defrule.
CLIPS> (set-current-module B)
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A
CLIPS> (list-defrules)
foo
For a total of 1 defrule.
CLIPS>
10.3 Specifying Modules
Commands such as undefrule and ppdefrule require the name of a construct on which to
operate. In previous versions of CLIPS, constructs were always referred to by their name only, so
it was sufficient just to pass the name of the construct to these commands. With modules,
however, it is possible to have a construct with the same name in two different modules. The
modules associated with a name can be specified either explicitly or implicitly. To explicitly
specify a name’s module the module name (a symbol) is listed followed by two colons, ::, and
then the name is listed. The module name followed by :: is referred to as a module specifier. For
example, MAIN::find-stuff, refers to the find-stuff construct in the MAIN module. A module can
also be implicitly specified since there is always a “current” module. The current module is
changed whenever a defmodule construct is defined or the set-current-module function is used.
The MAIN module is automatically defined by CLIPS and by default is the current module when
CLIPS is started or after a clear command is issued. Thus the name find-stuff would implicitly
have the MAIN module as its module when CLIPS is first started.
CLIPS> (clear)
CLIPS> (defmodule A)
CLIPS> (defglobal A ?*x* = 0)
CLIPS> (defmodule B)
CLIPS> (defglobal B ?*y* = 1)
CLIPS> (ppdefglobal y)
(defglobal B ?*y* = 1)
CLIPS> (ppdefglobal B::y)
(defglobal B ?*y* = 1)
CLIPS> (ppdefglobal x)
[PRNTUTIL1] Unable to find defglobal x.
CLIPS> (ppdefglobal A::x)
(defglobal A ?*x* = 0)
CLIPS>
10.4 Importing and Exporting Constructs
Unless specifically exported and imported, the constructs of one module may not be used by
another module. A construct is said to be visible or within scope of a module if that construct can
be used by the module. For example, if module B wants to use the foo deftemplate defined in
module A, then module A must export the foo deftemplate and module B must import the foo
deftemplate from module A.
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CLIPS> (clear)
CLIPS> (defmodule A)
CLIPS> (deftemplate A::foo (slot x))
CLIPS> (defmodule B)
CLIPS> (defrule B::bar (foo (x 3)) =>)
[PRNTUTIL2] Syntax Error: Check appropriate syntax for defrule
ERROR:
(defrule B::bar
(foo (
CLIPS> (clear)
CLIPS> (defmodule A (export deftemplate foo))
CLIPS> (deftemplate A::foo (slot x))
CLIPS> (defmodule B (import A deftemplate foo))
CLIPS> (defrule B::bar (foo (x 3)) =>)
CLIPS>
CLIPS will not allow a module or other construct to be defined that causes two constructs with
the same name to be visible within the same module.
10.4.1 Exporting Constructs
The export specification in a defmodule definition is used to indicate which constructs will be
accessible to other modules importing from the module being defined. Only deftemplates,
defclasses, defglobals, deffunctions, and defgenerics may be exported. A module may export any
valid constructs that are visible to it (not just constructs that it defines).
There are three different types of export specifications. First, a module may export all valid
constructs that are visible to it. This accomplished by following the export keyword with the
?ALL keyword. Second, a module may export all valid constructs of a particular type that are
visible to it. This accomplished by following the export keyword with the name of the construct
type followed by the ?ALL keyword. Third, a module may export specific constructs of a
particular type that are visible to it. This accomplished by following the export keyword with the
name of the construct type followed by the name of one or more visible constructs of the
specified type. In the following code, defmodule A exports all of its constructs; defmodule B
exports all of its deftemplates; and defmodule C exports the foo, bar, and yak defglobals.
(defmodule A (export ?ALL))
(defmodule B (export deftemplate ?ALL))
(defmodule C (export defglobal foo bar yak))
The ?NONE keyword may be used in place of the ?ALL keyword to indicate either that no
constructs are exported from a module or that no constructs of a particular type are exported
from a module.
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Defmethods and defmessage-handlers cannot be explicitly exported. Exporting a defgeneric
automatically exports all associated defmethods. Exporting a defclass automatically exports all
associated defmessage-handlers. Deffacts, definstances, and defrules cannot be exported.
10.4.2 Importing Constructs
The import specification in a defmodule definition is used to indicate which constructs the
module being defined will use from other modules. Only deftemplates, defclasses, defglobals,
deffunctions, and defgenerics may be imported.
There are three different types of import specifications. First, a module may import all valid
constructs that are visible to a specified module. This accomplished by following the import
keyword with a module name followed by the ?ALL keyword. Second, a module may import all
valid constructs of a particular type that are visible to a specified module. This accomplished by
following the import keyword with a module name followed by the name of the construct type
followed by the ?ALL keyword. Third, a module may import specific constructs of a particular
type that are visible to it. This accomplished by following the import keyword with a module
name followed by the name of the construct type followed by the name of one or more visible
constructs of the specified type. In the following code, defmodule A imports all of module D’s
constructs; defmodule B imports all of module D’s deftemplates; and defmodule C imports the
foo, bar, and yak defglobals from module D.
(defmodule A (import D ?ALL))
(defmodule B (import D deftemplate ?ALL))
(defmodule C (import D defglobal foo bar yak))
The ?NONE keyword may be used in place of the ?ALL keyword to indicate either that no
constructs are imported from a module or that no constructs of a particular type are imported
from a module.
Defmethods and defmessage-handlers cannot be explicitly imported. Importing a defgeneric
automatically imports all associated defmethods. Importing a defclass automatically imports all
associated defmessage-handlers. Deffacts, definstances, and defrules cannot be imported.
A module must be defined before it is used in an import specification. In addition, if specific
constructs are listed in the import specification, they must already be defined in the module
exporting them. It is not necessary to import a construct from the module in which it is defined in
order to use it. A construct can be indirectly imported from a module that directly imports and
then exports the module to be used.
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10.5 Importing and Exporting Facts and Instances
Facts and instances are “owned” by the module in which their corresponding deftemplate or
defclass is defined, not by the module which creates them. Facts and instances are thus visible
only to those modules that import the corresponding deftemplate or defclass. This allows a
knowledge base to be partitioned such that rules and other constructs can only “see” those facts
and instances that are of interest to them. Instance names, however, are global in scope, so it is
still possible to send messages to an instance of a class that is not in scope.
Example
CLIPS> (clear)
CLIPS> (defmodule A (export deftemplate foo bar))
CLIPS> (deftemplate A::foo (slot x))
CLIPS> (deftemplate A::bar (slot y))
CLIPS> (deffacts A::info (foo (x 3)) (bar (y 4)))
CLIPS> (defmodule B (import A deftemplate foo))
CLIPS> (reset)
CLIPS> (facts A)
f-1 (foo (x 3))
f-2 (bar (y 4))
For a total of 2 facts.
CLIPS> (facts B)
f-1 (foo (x 3))
For a total of 1 fact.
CLIPS>
10.5.1 Specifying Instance-Names
Instance-names are required to be unique regardless of the module that owns them. The syntax of
instance-names has been extended to allow module specifications (note that the left and right
brackets in bold are to be typed and do not indicate an optional part of the syntax).
Syntax
<instance-name> ::= [<symbol>] |
[::<symbol>] |
[<module>::symbol>]
Specifying just a symbol as the instance-name, such as [Rolls-Royce], will search for the
instance in all modules. Specifying only the :: before the name, such as [::Rolls-Royce], will
search for the instance first in the current module and then recursively in the imported modules
as defined in the module definition. Specifying both a symbol and a module name, such as
[CARS::Rolls-Royce], searches for the instance only in the specified module.
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10.6 Modules and Rule Execution
Each module has its own pattern-matching network for its rules and its own agenda. When a run
command is given, the agenda of the module that is the current focus is executed (note that the
reset and clear commands make the MAIN module the current focus). Rule execution continues
until another module becomes the current focus, no rules are left on the agenda, or the return
function is used from the RHS of a rule. Whenever a module that was focused on runs out of
rules on its agenda, the current focus is removed from the focus stack and the next module on the
focus stack becomes the current focus. Before a rule executes, the current module is changed to
the module in which the executing rule is defined (the current focus). The current focus can be
changed by using the focus command. See sections 5.2, 5.4.10.2, 12.12, and 13.12 for more
details.
Example
CLIPS> (clear)
CLIPS> (defmodule MAIN)
CLIPS>
(defrule MAIN::focus-example
=>
(printout t "Firing rule in module MAIN." crlf)
(focus A B))
CLIPS> (defmodule A)
CLIPS>
(defrule A::example-rule
=>
(printout t "Firing rule in module A." crlf))
CLIPS> (defmodule B)
CLIPS>
(defrule B::example-rule
=>
(printout t "Firing rule in module B." crlf))
CLIPS> (reset)
CLIPS> (run)
Firing rule in module MAIN.
Firing rule in module A.
Firing rule in module B.
CLIPS>
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Section 11:
Constraint Attributes
This section describes the constraint attributes that can be associated with deftemplates and
defclasses so that type checking can be performed on slot values when template facts and
instances are created. The constraint information is also analyzed for the patterns on the LHS of
a rule to determine if the specified constraints prevent the rule from ever firing.
Two types of constraint checking are supported: static and dynamic. When static constraint
checking is enabled, constraint violations are checked when function calls and constructs are
parsed. This includes constraint checking between patterns on the LHS of a rule when variables
are used in more than one slot. When dynamic constraint checking is enabled, newly created data
objects (such as deftemplate facts and instances) have their slot values checked for constraint
violations. Essentially, static constraint checking occurs when a CLIPS program is loaded and
dynamic constraint checking occurs when a CLIPS program is running. By default, static
constraint checking is enabled and dynamic constraint checking is disabled. The default behavior
can be changed by using the set-static-constraint-checking and
set-dynamic-constraint-checking functions.
Unless dynamic constraint checking is enabled, constraint information associated with constructs
is not saved when a binary image is created using the bsave command.
The general syntax for constraint attributes is shown following.
Syntax
<constraint-attribute> ::= <type-attribute> |
<allowed-constant-attribute> |
<range-attribute> |
<cardinality-attribute>
11.1 Type Attribute
The type attribute allows the types of values to be stored in a slot to be restricted.
Syntax
<type-attribute> ::= (type <type-specification>)
<type-specification> ::= <allowed-type>+ | ?VARIABLE
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<allowed-type>
::= SYMBOL | STRING | LEXEME |
INTEGER | FLOAT | NUMBER |
INSTANCE-NAME | INSTANCE-ADDRESS | INSTANCE |
EXTERNAL-ADDRESS | FACT-ADDRESS
Using NUMBER for this attribute is equivalent to using both INTEGER and FLOAT. Using
LEXEME for this attribute is equivalent to using both SYMBOL and STRING. Using
INSTANCE for this attribute is equivalent to using both INSTANCE-NAME and
INSTANCE-ADDRESS. ?VARIABLE allows any type to be stored.
11.2 Allowed Constant Attributes
The allowed constant attributes allow the constant values of a specific type that can be stored in a
slot to be restricted. The list of values provided should either be a list of constants of the
specified type or the keyword ?VARIABLE which means any constant of that type is allowed.
The allowed-values attribute allows the slot to be restricted to a specific set of values
(encompassing all types). Note the difference between using the attribute (allowed-symbols red
green blue) and (allowed-values red green blue). The allowed-symbols attribute states that if the
value is of type symbol, then its value must be one of the listed symbols. The allowed-values
attribute completely restricts the allowed values to the listed values. The allowed-classes
attribute does not restrict the slot value in the same manner as the other allowed constant
attributes. Instead, if this attribute is specified and the slot value is either an instance address or
instance name, then the class to which the instance belongs must be a class specified in the
allowed-classes attribute or be a subclass of one of the specified classes.
Syntax
<allowed-constant-attribute>
::= (allowed-symbols <symbol-list>) |
(allowed-strings <string-list>) |
(allowed-lexemes <lexeme-list> |
(allowed-integers <integer-list>) |
(allowed-floats <float-list>) |
(allowed-numbers <number-list>) |
(allowed-instance-names <instance-list>) |
(allowed-classes <class-name-list>)
(allowed-values <value-list>)
<symbol-list> ::= <symbol>+ | ?VARIABLE
<string-list> ::= <string>+ | ?VARIABLE
<lexeme-list> ::= <lexeme>+ | ?VARIABLE
<integer-list> ::= <integer>+ | ?VARIABLE
<float-list> ::= <float>+ | ?VARIABLE
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<number-list> ::= <number>+ | ?VARIABLE
<instance-name-list> ::= <instance-name>+ | ?VARIABLE
<class-name-list> ::= <class-name>+ | ?VARIABLE
<value-list> ::= <constant>+ | ?VARIABLE
Specifying the allowed-lexemes attribute is equivalent to specifying constant restrictions on both
symbols and strings. A string or symbol must match one of the constants in the attribute list.
Type conversion from symbols to strings and strings to symbols is not performed. Similarly,
specifying the allowed-numbers attribute is equivalent to specifying constant restrictions on both
integers and floats. In CLIPS 5.1, type conversion of integers to floats and floats to integers was
performed when using the allowed-numbers attribute (thus using allowed-numbers was not
equivalent to using both the allowed-integers and allowed-floats attributes together). In CLIPS
6.0, this type conversion is no longer performed. The allowed-instances attribute found in CLIPS
5.1 is no longer supported. The allowed-instance-names attribute should be used in its place.
11.3 Range Attribute
The range attribute allows a numeric range to be specified for a slot when a numeric value is
used in that slot. If a numeric value is not used in that slot, then no checking is performed.
Syntax
<range-attribute> ::= (range <range-specification>
<range-specification>)
<range-specification> ::= <number> | ?VARIABLE
Either integers or floats can be used in the range specification with the first value to the range
attribute signifying the minimum allowed value and the second value signifying the maximum
value. Integers will be temporarily converted to floats when necessary to perform range
comparisons. If the keyword ?VARIABLE is used for the minimum value, then the minimum
value is negative infinity (-∞). If the keyword ?VARIABLE is used for the maximum value, then
the maximum value is positive infinity (+∞). The range attribute cannot be used in conjunction
with the allowed-values, allowed-numbers, allowed-integers, or allowed-floats attributes.
11.4 Cardinality Attribute
The cardinality attribute restricts the number of fields that can be stored in a multifield slot. This
attribute can not be used with a single field slot.
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Syntax
<cardinality-attribute>
::= (cardinality <cardinality-specification>
<cardinality-specification>)
<cardinality-specification> ::= <integer> | ?VARIABLE
Only integers can be used in the cardinality specification with the first value to the cardinality
attribute signifying the minimum number of fields that can be stored in the slot and the second
value signifying the maximum number of fields which can be stored in the slot. If the keyword
?VARIABLE is used for the minimum value, then the minimum cardinality is zero. If the
keyword ?VARIABLE is used for the maximum value, then the maximum cardinality is positive
infinity (+∞). If the cardinality is not specified for a multifield slot, then it is assumed to be zero
to infinity.
The min-number-of-elements and max-number-of-elements attributes found in CLIPS 5.1 are no
longer supported. The cardinality attribute should be used in their place.
11.5 Deriving a Default Value From Constraints
Default values for deftemplate and instance slots are automatically derived from the constraints
for the slots if an explicit default value is not specified. The following rules are used (in order) to
determine the default value for a slot with an unspecified default value.
1) The default type for the slot is chosen from the list of allowed types for the slot in the
following order of precedence: SYMBOL, STRING, INTEGER, FLOAT,
INSTANCE-NAME, INSTANCE-ADDRESS, FACT-ADDRESS,
EXTERNAL-ADDRESS.
2) If the default type has an allowed constant restriction specified (such as the allowed-integers
attribute for the INTEGER type), then the first value specified in the allowed constant
attribute is chosen as the default value.
3) If the default value was not specified by step 2 and the default type is INTEGER or FLOAT
and the range attribute is specified, then the minimum range value is used as the default
value if it is not ?VARIABLE, otherwise, the maximum range value is used if it is not
?VARIABLE.
4) If the default value was not specified by step 2 or 3, then the default default value is used.
This value is nil for type SYMBOL, "" for type STRING, 0 for type INTEGER, 0.0 for type
FLOAT, [nil] for type INSTANCE-NAME, a pointer to a dummy instance for type
INSTANCE-ADDRESS, a pointer to a dummy fact for type FACT-ADDRESS, and the
NULL pointer for type EXTERNAL-ADDRESS.
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5) If the default value is being derived for a single field slot, then the default value derived
from steps 1 through 4 is used. The default value for a multifield slot is a multifield value of
length zero. However, if the multifield slot has a minimum cardinality greater than zero,
then a multifield value with a length of the minimum cardinality is created and the default
value that would be used for a single field slot is stored in each field of the multifield value.
11.6 Constraint Violation Examples
The following examples illustrate some of the types of constraint violations that CLIPS can
detect.
Example 1
CLIPS>
(deftemplate bar
(slot a (type SYMBOL INTEGER))
(slot b (type INTEGER FLOAT))
(slot c (type SYMBOL STRING)))
CLIPS>
(defrule error
(bar (a ?x))
(bar (b ?x))
(bar (c ?x))
=>)
[RULECSTR1] Variable ?x in CE #3 slot c
has constraint conflicts which make the pattern unmatchable
ERROR:
(defrule MAIN::error-4
(bar (a ?x))
(bar (b ?x))
(bar (c ?x))
=>)
CLIPS>
The first occurrence of the variable ?x in slot a of the first pattern restricts its allowed types to
either a symbol or integer. The second occurrence of ?x in slot b of the second pattern further
restricts its allowed types to only integers. The final occurence of ?x in the third pattern
generates an error because slot c expects ?x to be either a symbol or a string, but its only allowed
type is an integer.
Example 2
CLIPS>
(deftemplate foo (multislot x (cardinality ?VARIABLE 2)))
CLIPS>
(deftemplate bar (multislot y (cardinality ?VARIABLE 3)))
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CLIPS>
(deftemplate woz (multislot z (cardinality 7 ?VARIABLE)))
CLIPS>
(defrule MAIN::error
(foo (x $?x))
(bar (y $?y))
(woz (z $?x $?y))
=>)
[CSTRNCHK1] The group of restrictions found in CE #3
do not satisfy the cardinality restrictions for slot z
ERROR:
(defrule MAIN::error
(foo (x $?x))
(bar (y $?y))
(woz (z $?x $?y))
=>)
CLIPS>
The variable ?x, found in the first pattern, can have a maximum of two fields. The variable ?y,
found in the second pattern, can have a maximum of three fields. Added together, both variables
have a maximum of five fields. Since slot z in the the third pattern has a minimum cardinality of
seven, the variables ?x and ?y cannot satisfy the minimum cardinality restriction for this slot.
Example 3
CLIPS> (clear)
CLIPS> (deftemplate foo (slot x (type SYMBOL)))
CLIPS>
(defrule error
(foo (x ?x))
(test (> ?x 10))
=>)
[RULECSTR2] Previous variable bindings of ?x caused the type restrictions for
argument #1 of the expression (> ?x 10)
found in CE #2 to be violated
ERROR:
(defrule MAIN::error
(foo (x ?x))
(test (> ?x 10))
=>)
CLIPS>
The variable ?x, found in slot x of the first pattern, must be a symbol. Since the > function
expects numeric values for its arguments, an error occurs.
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Section 12:
Actions And Functions
This section describes various actions and functions which may be used on the LHS and RHS of
rules, from the top-level command prompt, and from other constructs such as deffunctions,
defmessage-handlers, and defmethods. The terms functions, actions, and commands should be
thought of interchangeably. However, when the term function is used it generally refers to a
function that returns a value. The term action refers to a function having no return value but
performing some basic operation as a side effect (such as printout). The term command refers to
functions normally entered at the top-level command prompt (such as the reset command, which
does not return a value, and the set-strategy command, which does return a value).
12.1 Predicate Functions
The following functions perform predicate tests.
12.1.1 Testing For Numbers
The numberp function returns the symbol TRUE if its argument is a float or integer, otherwise it
returns the symbol FALSE.
Syntax
(numberp <expression>)
12.1.2 Testing For Floats
The floatp function returns the symbol TRUE if its argument is a float, otherwise it returns the
symbol FALSE.
Syntax
(floatp <expression>)
12.1.3 Testing For Integers
The integerp function returns the symbol TRUE if its argument is an integer, otherwise it returns
the symbol FALSE.
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Syntax
(integerp <expression>)
12.1.4 Testing For Strings Or Symbols
The lexemep function returns the symbol TRUE if its argument is a string or symbol, otherwise
it returns the symbol FALSE.
Syntax
(lexemep <expression>)
12.1.5 Testing For Strings
The stringp function returns the symbol TRUE if its argument is a string, otherwise it returns the
symbol FALSE.
Syntax
(stringp <expression>)
12.1.6 Testing For Symbols
The symbolp function returns the symbol TRUE if its argument is a symbol, otherwise it returns
the symbol FALSE. This function may also be called using the name wordp.
Syntax
(symbolp <expression>)
12.1.7 Testing For Even Numbers
The evenp function returns the symbol TRUE if its argument is an even number, otherwise it
returns the symbol FALSE.
Syntax
(evenp <integer-expression>)
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12.1.8 Testing For Odd Numbers
The oddp function returns the symbol TRUE if its argument is an odd number, otherwise it
returns the symbol FALSE.
Syntax
(oddp <integer-expression>)
12.1.9 Testing For Multifield Values
The multifieldp function returns the symbol TRUE if its argument is a multifield value,
otherwise it returns the symbol FALSE. This function may also be called using the name
sequencep.
Syntax
(multifieldp <expression>)
12.1.10 Testing For External-Addresses
The pointerp function returns the symbol TRUE if its argument is an external-address, otherwise
it returns the symbol FALSE. External-addresses are discussed in further detail in the Advanced
Programming Guide.
Syntax
(pointerp <expression>)
12.1.11 Comparing for Equality
The eq function returns the symbol TRUE if its first argument is equal in value to all its
subsequent arguments, otherwise it returns the symbol FALSE. Note that eq compares types as
well as values. Thus, (eq 3 3.0) is FALSE since 3 is an integer and 3.0 is a float.
Syntax
(eq <expression> <expression>+)
Example
CLIPS> (eq foo bar mumble foo)
FALSE
CLIPS> (eq foo foo foo foo)
TRUE
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CLIPS> (eq 3 4)
FALSE
CLIPS>
12.1.12 Comparing for Inequality
The neq function returns the symbol TRUE if its first argument is not equal in value to all its
subsequent arguments, otherwise it returns the symbol FALSE. Note that neq compares types as
well as values. Thus, (neq 3 3.0) is TRUE since 3 is an integer and 3.0 is a float.
Syntax
(neq <expression> <expression>+)
Example
CLIPS> (neq foo bar yak bar)
TRUE
CLIPS> (neq foo foo yak bar)
FALSE
CLIPS> (neq 3 a)
TRUE
CLIPS>
12.1.13 Comparing Numbers for Equality
The = function returns the symbol TRUE if its first argument is equal in value to all its
subsequent arguments, otherwise it returns the symbol FALSE. Note that = compares only
numeric values and will convert integers to floats when necessary for comparison.
Syntax
(= <numeric-expression> <numeric-expression>+)
Example
CLIPS> (= 3 3.0)
TRUE
CLIPS> (= 4 4.1)
FALSE
CLIPS>
! Portability Note
Because the precision of floating point numbers varies from one machine to another, it is
possible for the numeric comparison functions to work correctly one machine and incorrectly on
another. In fact, you should be aware, even if code is not being ported, that roundoff error can
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cause erroneous results. For example, the following expression erroneously returns the symbol
TRUE because both numbers are rounded up to 0.6666666666666666667.
CLIPS> (= 0.66666666666666666666 0.66666666666666666667)
TRUE
CLIPS>
12.1.14 Comparing Numbers for Inequality
The <> function returns the symbol TRUE if its first argument is not equal in value to all its
subsequent arguments, otherwise it returns the symbol FALSE. Note that <> compares only
numeric values and will convert integers to floats when necessary for comparison.
Syntax
(<> <numeric-expression> <numeric-expression>+)
Example
CLIPS> (<> 3 3.0)
FALSE
CLIPS> (<> 4 4.1)
TRUE
CLIPS>
! Portability Note
See portability note in section 12.1.13.
12.1.15 Greater Than Comparison
The > function returns the symbol TRUE if for all its arguments, argument n-1 is greater than
argument n, otherwise it returns the symbol FALSE. Note that > compares only numeric values
and will convert integers to floats when necessary for comparison.
Syntax
(> <numeric-expression> <numeric-expression>+)
Example
CLIPS> (> 5 4 3)
TRUE
CLIPS> (> 5 3 4)
FALSE
CLIPS>
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! Portability Note
See portability note in section 12.1.13.
12.1.16 Greater Than or Equal Comparison
The >= function returns the symbol TRUE if for all its arguments, argument n-1 is greater than
or equal to argument n, otherwise it returns the symbol FALSE. Note that >= compares only
numeric values and will convert integers to floats when necessary for comparison.
Syntax
(>= <numeric-expression> <numeric-expression>+)
Example
CLIPS> (>= 5 5 3)
TRUE
CLIPS> (>= 5 3 5)
FALSE
CLIPS>
! Portability Note
See portability note in section 12.1.13.
12.1.17 Less Than Comparison
The < function returns the symbol TRUE if for all its arguments, argument n-1 is less than
argument n, otherwise it returns the symbol FALSE. Note that < compares only numeric values
and will convert integers to floats when necessary for comparison.
Syntax
(< <numeric-expression> <numeric-expression>+)
Example
CLIPS> (< 3 4 5)
TRUE
CLIPS> (< 3 5 4)
FALSE
CLIPS>
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! Portability Note
See portability note in section 12.1.13.
12.1.18 Less Than or Equal Comparison
The <= function returns the symbol TRUE if for all its arguments, argument n-1 is less than or
equal to argument n, otherwise it returns the symbol FALSE. Note that <= compares only
numeric values and will convert integers to floats when necessary for comparison.
Syntax
(<= <numeric-expression> <numeric-expression>+)
Example
CLIPS> (<= 3 5 5)
TRUE
CLIPS> (<= 5 3 5)
FALSE
CLIPS>
! Portability Note
See portability note in section 12.1.13.
12.1.19 Boolean And
The and function returns the symbol TRUE if each of its arguments evaluates to TRUE,
otherwise it returns the symbol FALSE. The and function performs short-circuited boolean
logic. Each argument of the function is evaluated from left to right. If any argument evaluates to
FALSE, then the symbol FALSE is immediately returned by the function.
Syntax
(and <expression>+)
12.1.20 Boolean Or
The or function returns the symbol TRUE if any of its arguments evaluates to TRUE, otherwise
it returns the symbol FALSE. The or function performs short-circuited boolean logic. Each
argument of the function is evaluated from left to right. If any argument evaluates to TRUE, then
the symbol TRUE is immediately returned by the function.
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Syntax
(or <expression>+)
12.1.21 Boolean Not
The not function returns the symbol TRUE if its argument evaluates to FALSE, otherwise it
returns the symbol FALSE.
Syntax
(not <expression>)
12.2 Multifield Functions
The following functions operate on multifield values.
12.2.1 Creating Multifield Values
This function appends any number of fields together to create a multifield value.
Syntax
(create$ <expression>*)
The return value of create$ is a multifield value regardless of the number or types of arguments
(single-field or multifield). Calling create$ with no arguments creates a multifield value of
length zero.
Example
CLIPS (create$ hammer drill saw screw pliers wrench)
(hammer drill saw screw pliers wrench)
CLIPS> (create$ (+ 3 4) (* 2 3) (/ 8 4))
(7 6 2.0)
CLIPS>
12.2.2 Specifying an Element
The nth$ function will return a specified field from a multifield value.
Syntax
(nth$ <integer-expression> <multifield-expression>)
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where the first argument should be an integer from 1 to the number of elements within the
second argument. The symbol nil will be returned if the first argument is greater than the number
of fields in the second argument.
Example
CLIPS> (nth$ 3 (create$ a b c d e f g))
c
CLIPS>
12.2.3 Finding an Element
The member$ function will tell if a single field value is contained in a multifield value.
Syntax
(member$ <expression> <multifield-expression>)
If the first argument is a single field value and is one of the fields within the second argument,
member$ will return the integer position of the field (from 1 to the length of the second
argument). If the first argument is a multifield value and this value is embedded in the second
argument, then the return value is a two field multifield value consisting of the starting and
ending integer indices of the first argument within the second argument. If neither of these
situations is satisfied, then FALSE is returned.
Example
CLIPS> (member$ blue (create$ red 3 "text" 8.7 blue))
5
CLIPS> (member$ 4 (create$ red 3 "text" 8.7 blue))
FALSE
CLIPS> (member$ (create$ b c) (create$ a b c d))
(2 3)
CLIPS>
12.2.4 Comparing Multifield Values
This function checks if one multifield value is a subset of another; i.e., if all the fields in the first
multifield value are also in the second multifield value.
Syntax
(subsetp <multifield-expression> <multifield-expression>)
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If the first argument is a subset of the second argument, the function returns TRUE; otherwise, it
returns FALSE. The order of the fields is not considered. If the first argument is bound to a
multifield of length zero, the subsetp function always returns TRUE.
Example
CLIPS> (subsetp (create$ hammer saw drill)
(create$ hammer drill wrench pliers saw))
TRUE
CLIPS> (subsetp (create$ wrench crowbar)
(create$ hammer drill wrench pliers saw))
FALSE
CLIPS>
12.2.5 Deletion of Fields in Multifield Values
This function deletes the specified range from a multifield value.
Syntax
(delete$ <multifield-expression>
<begin-integer-expression>
<end-integer-expression>)
The modified multifield value is returned, which is the same as <multifield-expression> with the
fields ranging from <begin-integer-expression> to <end-integer-expression> removed. To delete
a single field, the begin range field should equal the end range field.
Example
CLIPS> (delete$ (create$ hammer drill saw pliers wrench) 3 4)
(hammer drill wrench)
CLIPS> (delete$ (create$ computer printer hard-disk) 1 1)
(printer hard-disk)
CLIPS>
12.2.6 Creating Multifield Values from Strings.
This function constructs a multifield value from a string by using each field in a string as a field
in a new multifield value.
Syntax
(explode$ <string-expression>)
A new multifield value is created in which each delimited field in order in <string-expression> is
taken to be a field in the new multifield value that is returned. A string with no fields creates a
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multifield value of length zero. Fields other than symbols, strings, integer, floats, or instances
names (such as parentheses or variables) are converted to strings.
Example
CLIPS> (explode$ "hammer drill saw screw")
(hammer drill saw screw)
CLIPS> (explode$ "1 2 abc 3 4 \"abc\" \"def\"")
(1 2 abc 3 4 "abc" "def")
CLIPS> (explode$ "?x ~ )")
("?x" "~" ")")
CLIPS>
12.2.7 Creating Strings from Multifield Values
This function creates a single string from a multifield value.
Syntax
(implode$ <multifield-expression>)
Each field in <multifield-expression> in order is concatenated into a string value with a single
blank separating fields. The new string is returned.
Example
CLIPS> (implode$ (create$ hammer drill screwdriver))
"hammer drill screwdriver wrench pliers saw"
CLIPS> (implode$ (create$ 1 "abc" def "ghi" 2))
"1 "abc" def "ghi" 2"
CLIPS> (implode$ (create$ "abc def ghi"))
""abc def ghi""
CLIPS>
12.2.8 Extracting a Sub-sequence from a Multifield Value
This function extracts a specified range from a multifield value and returns a new multifield
value containing just the sub-sequence.
Syntax
(subseq$ <multifield-value>
<begin-integer-expression>
<end-integer-expression>)
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where the second and third arguments are integers specifying the begin and end fields of the
desired sub-sequence in <multifield-expression>.
Example
CLIPS> (subseq$ (create$ hammer drill wrench pliers) 3 4)
(wrench pliers)
CLIPS> (subseq$ (create$ 1 "abc" def "ghi" 2) 1 1)
(1)
CLIPS>
12.2.9 Replacing Fields within a Multifield Value
This function replaces a range of field in a multifield value with a series of single-field and/or
multifield values and returns a new multifield value containing the replacement values within the
original multifield value.
Syntax
(replace$ <multifield-expression>
<begin-integer-expression>
<end-integer-expression>
<single-or-multi-field-expression>+)
where <begin-integer-expression> to <end-integer-expression> is the range of values to be
replaced.
Example
CLIPS> (replace$ (create$ drill wrench pliers) 3 3 machete)
(drill wrench machete)
CLIPS> (replace$ (create$ a b c d) 2 3 x y (create$ q r s))
(a x y q r s d)
CLIPS>
12.2.10 Inserting Fields within a Multifield Value
This function inserts a series of single-field and/or multifield values at a specified location in a
multifield value with and returns a new multifield value containing the inserted values within the
original multifield value.
Syntax
(insert$ <multifield-expression>
<integer-expression>
<single-or-multi-field-expression>+)
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where <integer-expression> is the location where the values are to be inserted. This value must
be greater than or equal to 1. A value of 1 inserts the new value(s) at the beginning of the
<multifield-expression>. Any value greater than the length of the <multifield-expression>
appends the new values to the end of the <multifield-expression>.
Example
CLIPS> (insert$ (create$ a b c d) 1 x)
(x a b c d)
CLIPS> (insert$ (create$ a b c d) 4 y z)
(a b c y z d)
CLIPS> (insert$ (create$ a b c d) 5 (create$ q r))
(a b c d q r)
CLIPS>
12.2.11 Getting the First Field from a Multifield Value
This function returns the first field of a multifield value as a multifield value
Syntax
(first$ <multifield-expression>)
Example
CLIPS> (first$ (create$ a b c))
(a)
CLIPS> (first$ (create$))
()
CLIPS>
12.2.12 Getting All but the First Field from a Multifield Value
This function returns all but the first field of a multifield value as a multifield value.
Syntax
(rest$ <multifield-expression>)
Example
CLIPS> (rest$ (create$ a b c))
(b c)
CLIPS> (rest$ (create$))
()
CLIPS>
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12.2.13 Determining the Number of Fields in a Multifield Value
The length$ function returns an integer indicating the number of fields contained in a multifield
value. If the argument passed to length$ is not the appropriate type, a negative one (-1) is
returned.
Syntax
(length$ <multifield-expression>)
Example
CLIPS> (length$ (create$ a b c d e f g))
7
CLIPS>
12.2.14 Deleting Specific Values within a Multifield Value
This function deletes specific values contained within a multifield value and returns the modified
multifield value.
Syntax
(delete-member$ <multifield-expression> <expression>+)
where <expression>+ is one or more values to be deleted from <multifield-expression>. If
<expression> is a multifield value, the entire sequence must be contained within the first
argument in the correct order.
Example
CLIPS> (delete-member$ (create$ a b a c) b a)
(c)
CLIPS> (delete-member$ (create$ a b c c b a) (create$ b a))
(a b c c)
CLIPS>
12.2.15 Replacing Specific Values within a Multifield Value
This function replaces specific values contained within a multifield value and returns the
modified multifield value.
Syntax
(replace-member$ <multifield-expression> <substitute-expression>
<search-expression>+)
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where any <search-expression> that is contained within <multifield-expression> is replaced by
<substitute-expression>.
Example
CLIPS> (replace-member$ (create$ a b a b) (create$ a b a) a b)
(a b a a b a a b a a b a)
CLIPS> (replace-member$ (create$ a b a b) (create$ a b a) (create$ a b))
(a b a a b a)
CLIPS>
12.3 String Functions
The following functions perform operations that are related to strings.
12.3.1 String Concatenation
The str-cat function will concatenates its arguments into a single string.
Syntax
(str-cat <expression>*)
Each <expression> should be one of the following types: symbol, string, float, integer, or
instance-name.
Example
CLIPS> (str-cat "foo" bar)
"foobar"
CLIPS>
12.3.2 Symbol Concatenation
The sym-cat function will concatenate its arguments into a single symbol. It is functionally
identical to the str-cat function with the exception that the returned value is a symbol and not a
string.
Syntax
(sym-cat <expression>*)
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Each <expression> should be one of the following types: symbol, string, float, integer, or
instance-name.
12.3.3 Taking a String Apart
The sub-string function will retrieve a portion of a string from another string.
Syntax
(sub-string <integer-expression> <integer-expression>
<string-expression>)
where the first argument, counting from one, must be a number marking the beginning position
in the string and the second argument must be a number marking the ending position in the
string. If the first argument is greater than the second argument, a null string is returned.
Example
CLIPS> (sub-string 3 8 "abcdefghijkl")
"cdefgh"
CLIPS>
12.3.4 Searching a String
The str-index function will return the position of a string inside another string.
Syntax
(str-index <lexeme-expression> <lexeme-expression>)
where the second argument is searched for the first occurrence of the first argument. The
str-index function returns the integer starting position, counting from one, of the first argument
in the second argument or returns the symbol FALSE if not found.
Example
CLIPS> (str-index "def" "abcdefghi")
4
CLIPS> (str-index "qwerty" "qwertypoiuyt")
1
CLIPS> (str-index "qwerty" "poiuytqwer")
FALSE
CLIPS>
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12.3.5 Evaluating a Function within a String
The eval function evaluates the string as though it were entered at the command prompt.
Syntax
(eval <string-or-symbol-expression>)
where the only argument is the command, constant, or global variable to be executed. NOTE:
eval does not permit the use of local variables (except when the local variables are defined as
part of the command such as with an instance query function), nor will it evaluate any of the
construct definition forms (i.e., defrule, deffacts, etc.). The return value is the result of the
evaluation of the string (or FALSE if an error occurs).
The eval function is not available for binary-load only or run-time CLIPS configurations (see the
Advanced Programming Guide).
Example
CLIPS> (eval "(+ 3 4)")
7
CLIPS> (eval "(create$ a b c)")
(a b c)
CLIPS>
12.3.6 Evaluating a Construct within a String
The build function evaluates the string as though it were entered at the command prompt.
Syntax
(build <string-or-symbol-expression>)
where the only argument is the construct to be added. The return value is TRUE if the construct
was added (or FALSE if an error occurs).
The build function is not available for binary-load only or run-time CLIPS configurations (see
the Advanced Programming Guide).
Example
CLIPS> (clear)
CLIPS> (build "(defrule foo (a) => (assert (b)))")
TRUE
CLIPS> (rules)
foo
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For a total of 1 rule.
CLIPS>
12.3.7 Converting a String to Uppercase
The upcase function will return a string or symbol with uppercase alphabetic characters.
Syntax
(upcase <string-or-symbol-expression>)
Example
CLIPS> (upcase "This is a test of upcase")
"THIS IS A TEST OF UPCASE"
CLIPS> (upcase A_Word_Test_for_Upcase)
A_WORD_TEST_FOR_UPCASE
CLIPS>
12.3.8 Converting a String to Lowercase
The lowcase function will return a string or symbol with lowercase alphabetic characters.
Syntax
(lowcase <string-or-symbol-expression>)
Example
CLIPS> (lowcase "This is a test of lowcase")
"this is a test of lowcase"
CLIPS> (lowcase A_Word_Test_for_Lowcase)
a_word_test_for_lowcase
CLIPS>
12.3.9 Comparing Two Strings
The str-compare function will compare two strings to determine their logical relationship (i.e.,
equal to, less than, greater than). The comparison is performed character-by-character until the
strings are exhausted (implying equal strings) or unequal characters are found. The positions of
the unequal characters within the ASCII character set are used to determine the logical
relationship of unequal strings.
Syntax
(str-compare <string-or-symbol-expression>
<string-or-symbol-expression>)
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This function returns an integer representing the result of the comparison (0 if the strings are
equal, < 0 if the first argument < the second argument, and > 0 if the first argument > the second
argument).
Example
CLIPS> (< (str-compare "string1" "string2") 0)
TRUE ; since "1" < "2" in ASCII character set
CLIPS> (str-compare "abcd" "abcd")
0
CLIPS>
12.3.10 Determining the Length of a String
The str-length function returns the length of a string as an integer.
Syntax
(str-length <string-or-symbol-expression>)
Example
CLIPS> (str-length "abcd")
4
CLIPS> (str-length xyz)
3
CLIPS>
12.3.11 Checking the Syntax of a Construct or Function Call within a String
The function check-syntax allows the text representation of a construct or function call to be
checked for syntax and semantic errors.
Syntax
(check-syntax <construct-or-function-string>)
This function returns FALSE if there are no errors or warnings encountered parsing the construct
or function call. The symbol MISSING-LEFT-PARENTHESIS is returned if the first token is
not a left parenthesis. The symbol EXTRANEOUS-INPUT-AFTER-LAST-PARENTHESIS is
returned if there are additional tokens after the closing right parenthesis of the construct or
function call. If errors or warnings are encounted parsing, the a multifield of length two is
returned. The first field of the multifield is a string containing the text of the error message (or
the symbol FALSE if no errors were encountered). The second field of the multifield is a string
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containing the text of the warning message (or the symbol FALSE if no warnings were
encountered).
Example
CLIPS> (check-syntax "(defrule example =>)")
FALSE
CLIPS> (check-syntax "(defrule foo (number 40000000000000000000) =>)")
(FALSE "[SCANNER1] WARNING: Over or underflow of long long integer.
")
CLIPS> (check-syntax "(defrule example (3) =>)")
("
[PRNTUTIL2] Syntax Error: Check appropriate syntax for the first field of a
pattern.
ERROR:
(defrule MAIN::example
(3
" FALSE)
CLIPS>
12.3.12 Converting a String to a Field
The string-to-field function parses a string and converts its contents to a primitive data type.
Syntax
(string-to-field <string-or-symbol-expression>)
where the only argument is the string to be parsed. Essentially calling string-to-field with its
string argument is equivalent to calling the read function and manually typing the contents of the
string argument or reading it from a file. It is preferable to call string-to-field rather than eval to
convert a string to a primitive data type since the eval function is not available for binary-load
only or run-time CLIPS configurations (see the Advanced Programming Guide).
Example
CLIPS> (string-to-field "3.4")
3.4
CLIPS> (string-to-field "a b")
a
CLIPS>
12.4 The CLIPS I/O System
CLIPS uses a system called I/O routers to provide very flexible I/O while remaining portable. A
more complete discussion of I/O routers is covered in the Advanced Programming Guide.
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12.4.1 Logical Names
One of the key concepts of I/O routing is the use of logical names. Logical names allow
reference to an I/O device without having to understand the details of the implementation of the
reference. Many functions in CLIPS make use of logical names. A logical name can be either a
symbol, a number, or a string. Several logical names are predefined by CLIPS and are used
extensively throughout the CLIPS code. These are
Name
Description
stdin
The default for all user inputs. The read and readline
functions read from stdin if t is specified as the logical name.
stdout
The default for all user inputs. The read and readline
functions read from stdin if t is specified as the logical name.
wclips
The CLIPS prompt is sent to this logical name.
wdialog
All informational messages are sent to this logical name.
wdisplay
Requests to display CLIPS information, such as facts or
rules, are sent to this logical name.
werror
All error messages are sent to this logical name.
wwarning
All warning messages are sent to this logical name.
wtrace
All watch information is sent to this logical name (with the
exception of compilations which is sent to wdialog).
Any of these logical names may be used anywhere a logical name is expected.
12.4.2 Common I/O Functions
CLIPS provides some of the most commonly needed I/O capabilities through several predefined
functions.
12.4.2.1 Open
The open function allows a user to open a file from the RHS of a rule and attaches a logical
name to it. This function takes three arguments: (1) the name of the file to be opened; (2) the
logical name which will be used by other CLIPS I/O functions to access the file; and (3) an
optional mode specifier. The mode specifier must be one of the following strings:
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Mode
Means
r
Character read access. Specified file must exist.
w
Character write access. Existing content overwritten.
a
Character write access. Writes append to end of file.
rb
Binary read access. Specified file must exist.
wb
Binary write access. Existing content overwritten.
ab
Binary write access. Writes append to end of file.
If the mode is not specified, it defaults to character read access.
Syntax
(open <file-name> <logical-name> [<mode>])
The <file-name> must either be a string or symbol and may include directory specifiers. If a
string is used, the backslash (\) and any other special characters that are part of <file-name> must
be escaped with a backslash. The logical name should not have been used previously. The open
function returns TRUE if it was successful, otherwise FALSE.
Example
CLIPS> (open "myfile.clp" writeFile "w")
TRUE
CLIPS> (open "MS-DOS/directory/file.clp" readFile)
TRUE
CLIPS>
12.4.2.2 Close
The close function closes a file stream previously opened with the open command. The file is
specified by a logical name previously attached to the desired stream.
Syntax
(close [<logical-name>])
If close is called without arguments, all open files will be closed. The user is responsible for
closing all files opened during execution. If files are not closed, the contents are not guaranteed
correct, however, CLIPS will attempt to close all open files when the exit command is executed.
The close function returns TRUE if any files were successfully closed, otherwise FALSE.
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Example
CLIPS> (open "myfile.clp" writeFile "w")
TRUE
CLIPS> (open "MS-DOS/directory/file.clp" readFile)
TRUE
CLIPS> (close writeFile)
TRUE
CLIPS> (close writeFile)
FALSE
CLIPS> (close)
TRUE
CLIPS> (close)
FALSE
CLIPS>
12.4.2.3 Printout
The function printout allows output to a device attached to a logical name. The logical name
must be specified and the device must have been prepared previously for output (e.g., a file must
be opened first). To send output to stdout, use a t for the logical name. If the logical name nil is
used, the printout function does nothing.
Syntax
(printout <logical-name> <expression>*)
Any number of expressions may be placed in a printout to be printed. Each expression is
evaluated and printed (with no spaces added between each printed expression). The symbol crlf
used as an <expression> will force a carriage return/newline and may be placed anywhere in the
list of expressions to be printed. Similarly, the symbols tab, vtab, and ff will print respectively a
tab, a vertical tab, and a form feed. The appearance of these special symbols may vary from one
operating system to another. The printout function strips quotation marks from around strings
when it prints them. Fact-addresses, instance-addresses and external-addresses can be printed by
the printout function. This function has no return value.
Example
CLIPS> (printout t "Hello there!" crlf)
Hello There!
CLIPS> (open "data.txt" mydata "w")
TRUE
CLIPS> (printout mydata "red green")
CLIPS> (close)
TRUE
CLIPS>
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12.4.2.4 Read
The read function allows a user to input information for a single field. All of the standard field
rules (e.g., multiple symbols must be embedded within quotes) apply.
Syntax
(read [<logical-name>])
where <logical-name> is an optional parameter. If specified, read tries to read from whatever is
attached to the logical file name. If <logical-name> is t or is not specified, the function will read
from stdin. All the delimiters defined in section 2.3.1 can be used as delimiters. The read
function always returns a primitive data type. Spaces, carriage returns, and tabs only act as
delimiters and are not contained within the return value (unless these characters are included
within double quotes as part of a string). If an end of file (EOF) is encountered while reading,
read will return the symbol EOF. If errors are encountered while reading, the string "*** READ
ERROR ***" will be returned.
Example
CLIPS> (open "data.txt" mydata "w")
TRUE
CLIPS> (printout mydata "red green")
CLIPS> (close)
TRUE
CLIPS> (open "data.txt" mydata)
TRUE
CLIPS> (read mydata)
red
CLIPS> (read mydata)
green
CLIPS> (read mydata)
EOF
CLIPS> (close)
TRUE
CLIPS>
12.4.2.5 Readline
The readline function is similar to the read function, but it allows a whole string to be input
instead of a single field. Normally, read will stop when it encounters a delimiter. The readline
function only stops when it encounters a carriage return, a semicolon, or an EOF. Any tabs or
spaces in the input are returned by readline as a part of the string. The readline function returns
a string.
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Syntax
(readline [<logical-name>])
where <logical-name> is an optional parameter. If specified, readline tries to read from
whatever is attached to the logical file name. If <logical-name> is t or is not specified, the
function will read from stdin. As with the read function, if an EOF is encountered, readline will
return the symbol EOF. If an error is encountered during input, readline returns the string "***
READ ERROR ***".
Example
CLIPS> (open "data.txt" mydata "w")
TRUE
CLIPS> (printout mydata "red green")
CLIPS> (close)
TRUE
CLIPS> (open "data.txt" mydata)
TRUE
CLIPS> (readline mydata)
"red green"
CLIPS> (readline mydata)
EOF
CLIPS> (close)
TRUE
CLIPS>
12.4.2.6 Format
The format function allows a user to send formatted output to a device attached to a logical
name. It can be used in place of printout when special formatting of output information is
desired. Although a slightly more complicated function, format provides much better control
over how the output is formatted. The format commands are similar to the printf statement in C.
The format function always returns a string containing the formatted output. A logical name of
nil may be used when the formatted return string is desired without writing to a device.
Syntax
(format <logical-name> <string-expression> <expression>*)
If t is given, output is sent to stdout. The second argument to format, called the control string,
specifies how the output should be formatted. Subsequent arguments to format (the parameter list
for the control string) are the expressions which are to be output as indicated by the control
string. Format currently does not allow expressions returning multifield values to be included in
the parameter list.
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The control string consists of text and format flags. Text is output exactly as specified, and
format flags describe how each parameter in the parameter list is to be formatted. The first
format flag corresponds to the first value in the parameter list, the second flag corresponds to the
second value, etc. The format flags must be preceded by a percent sign (%) and are of the general
format
%-M.Nx
where x is one of the flags listed below, the minus sign is an optional justification flag, and M
and N are optional parameters which specify the field width and the precision argument (which
varies in meaning based on the format flag). If M is used, at least M characters will be output. If
more than M characters are required to display the value, format expands the field as needed. If
M starts with a 0 (e.g., %07d), a zero is used as the pad character; otherwise, spaces are used. If
N is not specified, it defaults to six digits for floating-point numbers. If a minus sign is included
before the M, the value will be left justified; otherwise the value is right justified.
Format
Flag
Meaning
c
Display parameter as a single character.
d
Display parameter as a long long integer. (The N specifier is the minimum
number of digits to be printed.)
f
Display parameter as a floating-point number (The N specifier is the
number of digits following the decimal point).
e
Display parameter as a floating-point using power of 10 notation (The N
specifier is the number of digits following the decimal point).
g
Display parameter in the most general format, whichever is shorter (the N
specifier is the number of significant digits to be printed).
o
Display parameter as an unsigned octal number. (The N specifier is the
minimum number of digits to be printed.)
x
Display parameter as an unsigned hexadecimal number. (The N specifier
is the minimum number of digits to be printed.)
s
Display parameter as a string. Strings will have the leading and trailing
quotes stripped. (The N specifier indicates the maximum number of
characters to be printed. Zero also cannot be used for the pad character.)
n
Put a new line in the output.
r
Put a carriage return in the output.
%
Put the percent character in the output.
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Example
CLIPS> (format t "Hello World!%n")
Hello World!
"Hello World!
"
CLIPS> (format nil "Integer: |%d|" 12)
"Integer: |12|"
CLIPS> (format nil "Integer: |%4d|" 12)
"Integer: | 12|"
CLIPS> (format nil "Integer: |%-04d|" 12)
"Integer: |12 |"
CLIPS> (format nil "Integer: |%6.4d|" 12)
"Integer: | 0012|"
CLIPS> (format nil "Float: |%f|" 12.01)
"Float: |12.010000|"
CLIPS> (format nil "Float: |%7.2f| "12.01)
"Float: | 12.01| "
CLIPS> (format nil "Test: |%e|" 12.01)
"Test: |1.201000e+01|"
CLIPS> (format nil "Test: |%7.2e|" 12.01)
"Test: |1.20e+01|"
CLIPS> (format nil "General: |%g|" 1234567890)
"General: |1.23457e+09|"
CLIPS> (format nil "General: |%6.3g|" 1234567890)
"General: |1.23e+09|"
CLIPS> (format nil "Hexadecimal: |%x|" 12)
"Hexadecimal: |c|"
CLIPS> (format nil "Octal: |%o|" 12)
"Octal: |14|"
CLIPS> (format nil "Symbols: |%s| |%s|" value-a1 capacity)
"Symbols: |value-a1| |capacity|"
CLIPS>
! Portability Note
The format function uses the C function sprintf as a base. Some systems may not support
sprintf or may not support all of these features, which may affect how format works.
12.4.2.7 Rename
The rename function is used to change the name of a file.
Syntax
(rename <old-file-name> <new-file-name>)
Both <old-file-name> and <new-file-name> must either be a string or symbol and may include
directory specifiers. If a string is used, the backslash (\) and any other special characters that are
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part of either <old-file-name> or <new-file-name> must be escaped with a backslash. The
rename function returns TRUE if it was successful, otherwise FALSE.
! Portability Note
The rename function uses the ANSI C function rename as a base.
12.4.2.8 Remove
The remove function is used to delete a file.
Syntax
(remove <file-name>)
The <file-name> must either be a string or symbol and may include directory specifiers. If a
string is used, the backslash (\) and any other special characters that are part of <file-name> must
be escaped with a backslash. The remove function returns TRUE if it was successful, otherwise
FALSE.
! Portability Note
The remove function uses the ANSI C function remove as a base.
12.4.2.9 Get Character
The get-char function allows a single character to be retrieved from a logical name.
Syntax
(get-char [<logical-name>])
where <logical-name> is an optional parameter. If specified, get-char tries to retrieve a character
from the specified logical file name. If <logical-name> is t or is not specified, the function will
read from stdin. The return value is the integer ASCII value of the character retrieved. The value
of -1 is returned if the end of file is encountered while retrieving a character.
Example
CLIPS> (open example.txt example "w")
TRUE
CLIPS> (printout example "ABC" crlf)
CLIPS> (close example)
TRUE
CLIPS> (open example.txt example)
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TRUE
CLIPS> (get-char example)
65
CLIPS> (format nil "%c" (get-char example))
"B"
CLIPS> (get-char example)
67
CLIPS> (get-char example)
10
CLIPS> (get-char example)
-1
CLIPS>
(progn (printout t "Press any character to continue...")
(get-char t))
Press any character to continue...
13
CLIPS> (close)
TRUE
CLIPS>
12.4.2.10 Read Number
The read-number function allows a user to input a single number using the localized format (if
one has been specified using the set-locale function). If a localized format has not been specified,
then the C format for a number is used.
Syntax
(read-number [<logical-name>])
where <logical-name> is an optional parameter. If specified, read-number tries to read from
whatever is attached to the logical file name. If <logical-name> is t or is not specified, the
function will read from stdin. If a number is successfully parsed, the read-number function will
return either an integer (if the number contained just a sign and digits) or a float (if the number
contained the localized decimal point character or an exponent). If an end of file (EOF) is
encountered while reading, read-number will return the symbol EOF. If errors are encountered
while reading, the string "*** READ ERROR ***" will be returned.
Example
CLIPS> (read-number)
34
34
CLIPS> (read-number)
34.0
34.0
CLIPS> (read-number)
23,0
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"*** READ ERROR ***"
CLIPS>
12.4.2.11 Set Locale
The set-locale function allows a user to specify a locale which affects the numeric format
behavior of the format and read-number functions. Before a number is printed by the format
function or is parsed by the read-number function, the locale is temporarily changed to the last
value specified to the set-locale function (or the default C locale if no value was previously
specified).
Syntax
(set-locale [<locale-string>])
where the optional argument <locale-string> is a string containing the new locale to be used by
the format and read-number functions. If <local-string> is specified, then the value of the
previous locale is returned. If <locale-string> is not specified, then the value of the current locale
is returned. A <locale-string> value of "" uses the native locale (and the specification of this
locale is dependent on the environment in which CLIPS is run). A <locale-string> of "C"
specifies the standard C locale (which is the default).
Example
;;; This example assumes that the native
;;; locale has been set to Germany.
CLIPS> (read-number)
3.21
3.21
CLIPS> (read-number)
3,21
"*** READ ERROR ***"
CLIPS> (format nil "%f" 3.1)
"3.100000"
CLIPS> (set-locale "")
"C"
CLIPS> (read-number)
3.21
"*** READ ERROR ***"
CLIPS> (read-number)
3,21
3.21
CLIPS> (format nil "%f" 3.1)
"3,100000"
CLIPS>
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! Portability Note
The CLIPS set-locale function uses the ANSI C function setlocale to temporarily change the
locale. Setting the native locale used by the setlocale function when <local-string> is specified as
the empty string "" varies from one operating system to another. For example, in Windows 7 the
native locale is set by clicking on the Start menu, selecting Control Panel, selecting Region and
Language, selecting the Formats tab, and then selecting a region from the drop-down menu such
as German (Germany). Alternately in Windows, the <local-string> could be specified as “DE”
for Germany.
In Mac OS X, the native local can be specified by launching System Preferences, clicking on
Language & Region, and then setting the region to Germany. However, this only works when
running CLIPS from the Terminal application. Alternately the <locale-string> could be specified
as “de_DE” to specify Germany for either the GUI or Terminal version of CLIPS.
12.5 Math Functions
CLIPS provides several functions for mathematical computations. They are split into two
packages: a set of standard math functions and a set of extended math functions.
12.5.1 Standard Math Functions
The standard math functions are listed below. These functions should be used only on numeric
arguments. An error message will be printed if a string argument is passed to a math function.
12.5.1.1 Addition
The + function returns the sum of its arguments. Each of its arguments should be a numeric
expression. Addition is performed using the type of the arguments provided unless mixed mode
arguments (integer and float) are used. In this case, the function return value and integer
arguments are converted to floats after the first float argument has been encountered. This
function returns a float if any of its arguments is a float, otherwise it returns an integer.
Syntax
(+ <numeric-expression> <numeric-expression>+)
Example
CLIPS> (+ 2 3 4)
9
CLIPS> (+ 2 3.0 5)
10.0
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CLIPS> (+ 3.1 4.7)
7.8
CLIPS>
12.5.1.2 Subtraction
The - function returns the value of the first argument minus the sum of all subsequent arguments.
Each of its arguments should be a numeric expression. Subtraction is performed using the type of
the arguments provided unless mixed mode arguments (integer and float) are used. In this case,
the function return value and integer arguments are converted to floats after the first float
argument has been encountered. This function returns a float if any of its arguments is a float,
otherwise it returns an integer.
Syntax
(- <numeric-expression> <numeric-expression>+)
Example
CLIPS> (- 12 3 4)
5
CLIPS> (- 12 3.0 5)
4.0
CLIPS> (- 4.7 3.1)
1.6
CLIPS>
12.5.1.3 Multiplication
The * function returns the product of its arguments. Each of its arguments should be a numeric
expression. Multiplication is performed using the type of the arguments provided unless mixed
mode arguments (integer and float) are used. In this case, the function return value and integer
arguments are converted to floats after the first float argument has been encountered. This
function returns a float if any of its arguments is a float, otherwise it returns an integer.
Syntax
(* <numeric-expression> <numeric-expression>+)
Example
CLIPS> (* 2 3 4)
24
CLIPS> (* 2 3.0 5)
30.0
CLIPS> (* 3.1 4.7)
14.57
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CLIPS>
12.5.1.4 Division
The / function returns the value of the first argument divided by each of the subsequent
arguments. Each of its arguments should be a numeric expression. Division is performed using
the type of the arguments provided unless mixed mode arguments (integer and float) are used. In
this case, the function return value and integer arguments are converted to floats after the first
float argument has been encountered. By default, the dividend (the first argument) is
automatically converted to a floating point number so that the result is a floating pointer number.
The function set-auto-float-dividend can be used to control this behavior. If for example, the
auto-float feature is disabled, the expression (/ 4 3 4.0) evaluates to 0.25 as opposed to
0.333333333 if this feature were enabled. This function returns a float if any of its arguments is a
float, otherwise it returns an integer.
Syntax
(/ <numeric-expression> <numeric-expression>+)
Example
CLIPS> (/ 4 2)
2.0
CLIPS> (/ 4.0 2.0)
2.0
CLIPS> (/ 24 3 4)
2.0
CLIPS>
12.5.1.5 Integer Division
The div function returns the value of the first argument divided by each of the subsequent
arguments. Each of its arguments should be a numeric expression. Each argument is
automatically converted to an integer and integer division is performed. This function returns an
integer.
Syntax
(div <numeric-expression> <numeric-expression>+)
Example
CLIPS> (div 4 2)
2
CLIPS> (div 5 2)
2
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CLIPS> (div 33 2 3 5)
1
CLIPS>
12.5.1.6 Maximum Numeric Value
The max function returns the value of its largest numeric argument. Each of its arguments should
be a numeric expression. When necessary, integers are temporarily converted to floats for
comparison. The return value will either be integer or float (depending upon the type of the
largest argument).
Syntax
(max <numeric-expression>+)
Example
CLIPS> (max 3.0 4 2.0)
4
CLIPS>
12.5.1.7 Minimum Numeric Value
The min function returns the value of its smallest numeric argument. Each of its arguments
should be a numeric expression. When necessary, integers are temporarily converted to floats for
comparison. The return value will either be integer or float (depending upon the type of the
smallest argument).
Syntax
(min <numeric-expression>+)
Example
CLIPS> (min 4 0.1 -2.3)
-2.3
CLIPS>
12.5.1.8 Absolute Value
The abs function returns the absolute value of its only argument (which should be a numeric
expression). The return value will either be integer or float (depending upon the type the
argument).
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Syntax
(abs <numeric-expression>)
Example
CLIPS> (abs 4.0)
4.0
CLIPS> (abs -2)
2
CLIPS>
12.5.1.9 Convert To Float
The float function converts its only argument (which should be a numeric expression) to type
float and returns this value.
Syntax
(float <numeric-expression>)
Example
CLIPS> (float 4.0)
4.0
CLIPS> (float -2)
-2.0
CLIPS>
12.5.1.10 Convert To Integer
The integer function converts its only argument (which should be a numeric expression) to type
integer and returns this value.
Syntax
(integer <numeric-expression>)
Example
CLIPS> (integer 4.0)
4
CLIPS> (integer -2)
-2
CLIPS>
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12.5.2 Extended Math Functions
In addition to standard math functions, CLIPS also provides a large number of scientific and
trigonometric math functions for more extensive computations. Although included in the generic
version of CLIPS, if an expert system does not need these capabilities, these functions may be
excluded from the executable element of CLIPS to provide more memory (see the Advanced
Programming Guide).
12.5.2.1 Trigonometric Functions
The following trigonometric functions take one numeric argument and return a floating-point
number. The argument is expected to be in radians.
Function
Returns
acos
arccosine
acot
arccotangent
acsc
arccosecant
asec
arcsecant
asin
arcsine
atan
arctangent
cos
cosine
cot
cotangent
csc
cosecant
sec
secant
sin
sine
tan
tangent
Function
Returns
acosh
hyperbolic arccosine
acoth
hyperbolic arccotangent
acsch
hyperbolic arccosecant
asech
hyperbolic arcsecant
asinh
hyperbolic arcsine
atanh
hyperbolic arctangent
cosh
hyperbolic cosine
coth
hyperbolic cotangent
csch
hyperbolic cosecant
sech
hyperbolic secant
sinh
hyperbolic sine
tanh
hyperbolic tangent
Example
CLIPS> (cos 0)
1.0
CLIPS> (acos 1.0)
0.0
CLIPS>
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12.5.2.2 Convert From Degrees to Grads
The deg-grad function converts its only argument (which should be a numeric expression) from
units of degrees to units of grads (360 degrees = 400 grads). The return value of this function is a
float.
Syntax
(deg-grad <numeric-expression>)
Example
CLIPS> (deg-grad 90)
100.0
CLIPS>
12.5.2.3 Convert From Degrees to Radians
The deg-rad function converts its only argument (which should be a numeric expression) from
units of degrees to units of radians (360 degrees = 2π radians). The return value of this function
is a float.
Syntax
(deg-rad <numeric-expression>)
Example
CLIPS> (deg-rad 180)
3.141592653589793
CLIPS>
12.5.2.4 Convert From Grads to Degrees
The grad-deg function converts its only argument (which should be a numeric expression) from
units of grads to units of degrees (360 degrees = 400 grads). The return value of this function is a
float.
Syntax
(grad-deg <numeric-expression>)
Example
CLIPS> (grad-deg 100)
90.0
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CLIPS>
12.5.2.5 Convert From Radians to Degrees
The rad-deg function converts its only argument (which should be a numeric expression) from
units of radians to units of degrees (360 degrees = 2π radians). The return value of this function
is a float.
Syntax
(rad-deg <numeric-expression>)
Example
CLIPS> (rad-deg 3.141592653589793)
180.0
CLIPS>
12.5.2.6 Return the Value of π
The pi function returns the value of π (3.141592653589793...) as a float.
Syntax
(pi)
Example
CLIPS> (pi)
3.141592653589793
CLIPS>
12.5.2.7 Square Root
The sqrt function returns the square root of its only argument (which should be a numeric
expression) as a float.
Syntax
(sqrt <numeric-expression>)
Example
CLIPS> (sqrt 9)
3.0
CLIPS>
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12.5.2.8 Power
The ** function raises its first argument to the power of its second argument and returns this
value as a float.
Syntax
(** <numeric-expression> <numeric-expression>)
Example
CLIPS> (** 3 2)
9.0
CLIPS>
12.5.2.9 Exponential
The exp function raises the value e (the base of the natural system of logarithms, having a value
of approximately 2.718...) to the power specified by its only argument and returns this value as a
float.
Syntax
(exp <numeric-expression>)
Example
CLIPS> (exp 1)
2.718281828459045
CLIPS>
12.5.2.10 Logarithm
Given n (the only argument) and the value e is the base of the natural system of logarithms, the
log function returns the float value x such that the following equation is satisfied:
n = ex
Syntax
(log <numeric-expression>)
Example
CLIPS> (log 2.718281828459045)
1.0
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CLIPS>
12.5.2.11 Logarithm Base 10
Given n (the only argument), the log10 function returns the float value x such that the following
equation is satisfied:
n = 10x
Syntax
(log10 <numeric-expression>)
Example
CLIPS> (log10 100)
2.0
CLIPS>
12.5.2.12 Round
The round function rounds its only argument (which should be a numeric expression) toward the
closest integer. If the argument is exactly between two integers, it is rounded down. The return
value of this function is an integer.
Syntax
(round <numeric-expression>)
Example
CLIPS> (round 3.6)
4
CLIPS>
12.5.2.13 Modulus
The mod function returns the remainder of the result of dividing its first argument by its second
argument (assuming that the result of division must be an integer). It returns an integer if both
arguments are integers, otherwise it returns a float.
Syntax
(mod <numeric-expression> <numeric-expression>)
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Example
CLIPS> (mod 5 2)
1
CLIPS> (mod 3.7 1.2)
0.1
CLIPS>
12.6 Procedural Functions
The following are functions which provide procedural programming capabilities as found in
languages such as Pascal, C and Ada.
12.6.1 Binding Variables
Occasionally, it is important to create new variables or to modify the value of previously bound
variables on the RHS of a rule. The bind function provides this capability.
Syntax
(bind <variable> <expression>*)
where the first argument to bind, <variable>, is the local or global variable to be bound (it may
have been bound previously). The bind function may also be used within a message-handler's
body to set a slot's value.
If no <expression> is specified, then local variables are unbound and global variables are reset to
their original value. If one <expression> is specified, then the value of <variable> is set to the
return value from evaluating <expression>. If more than one <expression> is specified, then all
of the <expressions> are evaluated and grouped together as a multifield value and the resulting
value is stored in <variable>.
The bind function returns the symbol FALSE when a local variable is unbound, otherwise, the
return value is the value to which <variable> is set.
Example 1
CLIPS> (defglobal ?*x* = 3.4)
CLIPS> ?*x*
3.4
CLIPS> (bind ?*x* (+ 8 9))
17
CLIPS> ?*x*
17
CLIPS> (bind ?*x* (create$ a b c d))
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(a b c d)
CLIPS> ?*x*
(a b c d)
CLIPS> (bind ?*x* d e f)
(d e f)
CLIPS> ?*x*
(d e f)
CLIPS> (bind ?*x*)
3.4
CLIPS> ?*x*
3.4
CLIPS> (bind ?x 32)
32
CLIPS> ?x
32
CLIPS> (reset)
CLIPS> ?x
[EVALUATN1] Variable x is unbound
FALSE
CLIPS>
Example 2
CLIPS>
(defclass A (is-a USER)
(slot x)
(slot y))
CLIPS>
(defmessage-handler A init after ()
(bind ?self:x 3)
(bind ?self:y 4))
CLIPS> (make-instance a of A)
[a]
CLIPS> (send [a] print)
[a] of A
(x 3)
(y 4)
CLIPS>
12.6.2 If...then...else Function
The if function provides an if...then...else structure to allow for conditional execution of a set of
actions.
Syntax
(if <expression>
then
<action>*
[else
<action>*])
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Any number of allowable actions may be used inside of the then or else portion, including
another if...then...else structure. The else portion is optional. If <expression> evaluates to
anything other than the symbol FALSE, then the actions associated with the then portion are
executed. Otherwise, the actions associated with the else portion are executed. The return value
of the if function is the value of the last <expression> or <action> evaluated.
Example
(defrule closed-valves
(temp high)
(valve ?v closed)
=>
(if (= ?v 6)
then
(printout t "The special valve " ?v " is closed!" crlf)
(assert (perform special operation))
else
(printout t "Valve " ?v " is normally closed" crlf)))
Note that this rule could have been accomplished just as easily with two rules, and that it is
usually better to accomplish this with two rules.
(defrule closed-valves-number-6
(temp high)
(valve 6 closed)
=>
(printout t "The special valve 6 is closed!" crlf)
(assert (perform special operation)))
(defrule closed-valves-other-than-6
(temp high)
(valve ?v&~6 closed)
=>
(printout t "Valve " ?v " is normally closed" crlf))
12.6.3 While
The while function is provided to allow simple looping. Its use is similar to that of the if
function.
Syntax
(while <expression> [do]
<action>*)
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Again, all predicate functions are available for use in while. Any number of allowable actions
may be placed inside the while block, including if...then...else or additional while structures.
The test is performed prior to the first execution of the loop. The actions within the while loop
are executed until <expression> evaluates to the symbol FALSE. The while may optionally
include the symbol do after the condition and before the first action. The break and return
functions can be used to terminate the loop prematurely. The return value of this function is
FALSE unless the return function is used to terminate the loop.
Example
(defrule open-valves
(valves-open-through ?v)
=>
(while (> ?v 0)
(printout t "Valve " ?v " is open" crlf)
(bind ?v (- ?v 1))))
12.6.4 Loop-for-count
The loop-for-count function is provided to allow simple iterative looping.
Syntax
(loop-for-count <range-spec> [do] <action>*)
<range-spec> ::= <end-index> |
(<loop-variable> <start-index> <end-index>) |
(<loop-variable> <end-index>)
<start-index> ::= <integer-expression>
<end-index> ::= <integer-expression>
Performs the given actions the number of times specified by <range-spec>. If <start-index> is
not given, it is assumed to be one. If <start-index> is greater than <end-index>, then the body of
the loop is never executed. The integer value of the current iteration can be examined with the
loop variable, if specified.The break and return functions can be used to terminate the loop
prematurely. The return value of this function is FALSE unless the return function is used to
terminate the loop. Variables from an outer scope may be used within the loop, but the loop
variable (if specified) masks any outer variables of the same name. Loops can be nested.
Example
CLIPS> (loop-for-count 2 (printout t "Hello world" crlf))
Hello world
Hello world
FALSE
CLIPS>
(loop-for-count (?cnt1 2 4) do
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(loop-for-count (?cnt2 1 3) do
(printout t ?cnt1 " " ?cnt2 crlf)))
2 1
2 2
2 3
3 1
3 2
3 3
4 1
4 2
4 3
FALSE
CLIPS>
12.6.5 Progn
The progn function evaluates all of its arguments and returns the value of the last argument.
Syntax
(progn <expression>*)
Example
CLIPS> (progn (setgen 5) (gensym))
gen5
CLIPS>
12.6.6 Progn$
The progn$ function performs a set of actions for each field of a multifield value. The field of
the current iteration can be examined with <loop-variable>, if specified. The index of the current
iteration can be examined with <loop-variable>-index. The progn$ function can use variables
from outer scopes, and the return and break functions can also be used within a progn$ as long
as they are valid in the outer scope. The return value of this function is the return value of the last
action performed for the last field in the multifield value.
Syntax
(progn$ <list-spec> <expression>*)
<list-spec> ::= <multifield-expression> |
(<list-variable> <multifield-expression>)
Example
CLIPS> (progn$ (?field (create$ abc def ghi))
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(printout t "--> " ?field " " ?field-index " <--" crlf))
--> abc 1 <--
--> def 2 <--
--> ghi 3 <--
CLIPS>
12.6.7 Return
The return function immediately terminates the currently executing deffunction, generic
function method, message-handler, defrule RHS, or certain instance set query functions
(do-for-instance, do-for-all-instances and delayed-do-for-all-instances). Without any
arguments, there is no return value. However, if an argument is included, its evaluation is given
as the return value of the deffunction , method or message-handler.
The return function can only be used within the actions of deffunctions, methods and
message-handlers, defrules, or the instance set query functions previously listed. If used on the
RHS of a rule, the current focus is removed from the focus stack. In addition, return should not
be used as an argument to another function call. If used within an instance set query function, the
return function is only valid if it is applicable in the outer scope of the query.
Syntax
(return [<expression>])
Example
CLIPS>
(deffunction sign (?num)
(if (> ?num 0) then
(return 1))
(if (< ?num 0) then
(return -1))
0)
CLIPS> (sign 5)
1
CLIPS> (sign -10)
-1
CLIPS> (sign 0)
0
CLIPS>
12.6.8 Break
The break function immediately terminates the currently iterating while loop, loop-for-count
execution, progn execution, progn$ execution, foreach execution, or certain instance set query
functions (do-for-instance, do-for-all-instances and delayed-do-for-all-instances).
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The break function can only be used within the actions of a while loop, loop-for-count
execution, progn execution, progn$ execution, foreach execution, or the specified instance set
queries previously listed. Other uses will have no effect. The break cannot be used within a
progn unless it is valid for the outer scope of the progn. In addition, break should not be used
as an argument to another function call.
Syntax
(break)
Example
CLIPS>
(deffunction iterate (?num)
(bind ?i 0)
(while TRUE do
(if (>= ?i ?num) then
(break))
(printout t ?i " ")
(bind ?i (+ ?i 1)))
(printout t crlf))
CLIPS> (iterate 1)
0
CLIPS> (iterate 10)
0 1 2 3 4 5 6 7 8 9
CLIPS>
12.6.9 Switch
The switch function allows a particular group of actions (among several groups of actions) to be
performed based on a specified value.
Syntax
(switch <test-expression>
<case-statement>*
[<default-statement>])
<case-statement> ::=
(case <comparison-expression> then <action>*)
<default-statement> ::= (default <action>*)
As indicated by the BNF, the optional default statement must succeed all case statements. None
of the case comparison expressions should be the same.
The switch function evaluates the <test-expression> first and then evaluates each
<comparison-expression> in order of definition. Once the evaluation of the
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<comparison-expression> is equivalent to the evaluation of the <test-expression>, the actions of
that case are evaluated (in order) and the switch function is terminated. If no cases are satisfied,
the default actions (if any) are evaluated (in order).
The return value of the switch function is the last action evaluated in the switch function. If no
actions are evaluated, the return value is the symbol FALSE.
Example
CLIPS> (defglobal ?*x* = 0)
CLIPS> (defglobal ?*y* = 1)
CLIPS>
(deffunction foo (?val)
(switch ?val
(case ?*x* then *x*)
(case ?*y* then *y*)
(default none)))
CLIPS> (foo 0)
*x*
CLIPS> (foo 1)
*y*
CLIPS> (foo 2)
none
CLIPS>
12.6.10 Foreach
The foreach function performs a set of actions for each field of a multifield value. The field of
the current iteration can be examined with <loop-variable>, if specified. The index of the current
iteration can be examined with <loop-variable>-index. The foreach function can use variables
from outer scopes, and the return and break functions can also be used within a foreach as long
as they are valid in the outer scope. The return value of this function is the return value of the last
action performed for the last field in the multifield value.
Syntax
(foreach <list-variable> <multifield-expression> <expression>*)
Example
CLIPS> (foreach ?field (create$ abc def ghi)
(printout t "--> " ?field " " ?field-index " <--" crlf))
--> abc 1 <--
--> def 2 <--
--> ghi 3 <--
CLIPS>
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! Portability Note
The foreach function provides the same functionality as the progn$ function, but uses different
syntax with a more meaningful function name. It is provided for compatibility with Jess (Java
Expert System Shell).
12.7 Miscellaneous Functions
The following are additional functions for use within CLIPS.
12.7.1 Gensym
The gensym function returns a special, sequenced symbol that can be stored as a single field.
This is primarily for tagging patterns that need a unique identifier, but the user does not care
what the identifier is. Multiple calls to gensym are guaranteed to return different identifiers of
the form
genX
where X is a positive integer. The first call to gensym returns gen1; all subsequent calls
increment the number. Note that gensym is not reset after a call to clear. If users plan to use the
gensym feature, they should avoid creating facts which include a user-defined field of this form.
Example
(assert (new-id (gensym) flag1 7))
which, on the first call, generates a fact of the form
(new-id gen1 flag1 7)
12.7.2 Gensym*
The gensym* function is similar to the gensym function, however, it will produce a unique
symbol that does not currently exist within the CLIPS environment.
Example
CLIPS> (setgen 1)
1
CLIPS> (assert (gen1 gen2 gen3))
<Fact-1>
CLIPS> (gensym)
gen1
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CLIPS> (gensym*)
gen4
CLIPS>
12.7.3 Setgen
The setgen function allows the user to set the starting number used by gensym and gensym*
(see sections 12.7.1 and 12.7.2).
Syntax
(setgen <integer-expression>)
where <intger-expression> must be a positive integer value and is the value returned by this
function. All subsequent calls to gensym will return a sequenced symbol with the numeric
portion of the symbol starting at <integer-expression>.
Example
CLIPS> (setgen 32)
32
CLIPS>
After this, calls to gensym will return gen32, gen33, etc.
12.7.4 Random
The random function returns a “random” integer value. It is patterned after the ANSI standard
rand library function and therefore may not be available on all platforms.
Syntax
(random [<start-integer-expression> <end-integer-expression>])
where <start-integer-expression> and <end-integer-expression> if specified indicate the range of
values to which the randomly generated integer is limited.
Example
(defrule roll-the-dice
(roll-the-dice)
=>
(bind ?roll1 (random 1 6))
(bind ?roll2 (random 1 6))
(printout t "Your roll is: " ?roll1 " " ?roll2 crlf))
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12.7.5 Seed
The seed function seeds the random number generator. It is patterned after the ANSI standard
seed library function and therefore may not be available on all platforms.
Syntax
(seed <integer-expression>)
where <integer-expression> is the integer seed value and the function has no return value.
12.7.6 Time
The time function returns a floating-point value representing the elapsed seconds since the
system reference time.
Syntax
(time)
! Portability Note
Not all operating systems/compilers provide this function. The code is stored in the sysdep.c file,
and the default coding for generic CLIPS is a non-functional stub that returns zero for the time.
12.7.7 Number of Fields or Characters in a Data Object
The length function returns an integer for the number of fields bound to a multifield value or the
length in characters of a string or symbol.
Syntax
(length <string-symbol-or-multifield-expression>)
If the argument given to length is not the appropriate type, a negative one (-1) is returned. This
function may also be called using the name length$.
Example
CLIPS> (length (create$ a b c d e f g))
7
CLIPS> (length "cat")
3
CLIPS>
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12.7.8 Determining the Restrictions for a Function
The get-function-restrictions function can be used to gain access to the restriction string
associated with a CLIPS or user defined function. The restriction string contains information on
the number and types of arguments that a function expects. See section 3.1 of the Advanced
Programming Guide for the meaning of the characters which compose the restriction string.
Syntax
(get-function-restrictions <function-name>)
Example
CLIPS> (get-function-restrictions +)
"2*n"
CLIPS>
12.7.9 Sorting a List of Values
The function sort allows a list of values to be sorted based on a user specified comparison
function.
Syntax
(sort <comparison-function-name> <expression>*)
This function returns a multifield value containing the sorted values specified as arguments. The
comparison function used for sorting should accept exactly two arguments and can be a user-
defined function, a generic function, or a deffunction. Given two adjacent arguments from the
list to be sorted, the comparison function should return TRUE if its first argument should come
after its second argument in the sorted list.
Example
CLIPS> (sort > 4 3 5 7 2 7)
(2 3 4 5 7 7)
CLIPS>
(deffunction string> (?a ?b)
(> (str-compare ?a ?b) 0))
CLIPS> (sort string> ax aa bk mn ft m)
(aa ax bk ft m mn)
CLIPS>
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12.7.10 Calling a Function
The function funcall constructs a function call from its arguments and then evaluates the
function call. The first argument should be the name of a user-defined function, deffunction, or
generic function. The remaining arguments are evaluated and then passed to the specified
function when it is evaluated. Functions that are invoked using specialized syntax, such as the
assert command (which uses parentheses to delimit both slot and function names), may not be
called using funcall.
Syntax
(funcall (function-name> <expression>*)
Example
CLIPS> (funcall delete$ (create$ a b c) 2 2)
(a c)
CLIPS> (funcall + 1 2 (expand$ (create$ 3 4)))
10
CLIPS>
12.7.11 Timing Functions and Commands
The function timer returns the number of seconds elapsed evaluating a series of expressions.
Syntax
(timer <expression>*)
Example
CLIPS> (timer (loop-for-count 10000 (+ 3 4)))
0.0416709999999512
CLIPS>
12.7.12 Determining the Operating System
The operating-system function returns a symbol indicating the opertating system on which
CLIPS is running. Possible return values are VMS, UNIX-V, UNIX-7, LINUX, DARWIN,
MAC-OS-X, DOS, WINDOWS, and UNKNOWN.
Syntax
(operating-system)
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12.8 Deftemplate Functions
The following functions provide ancillary capabilities for the deftemplate construct.
12.8.1 Determining the Module in which a Deftemplate is Defined
This function returns the module in which the specified deftemplate name is defined.
Syntax
(deftemplate-module <deftemplate-name>)
12.8.2 Getting the Allowed Values for a Deftemplate Slot
This function groups the allowed values for a slot (specified in any of allowed-… attributes for
the slots) into a multifield variable. If no allowed-… attributes were specified for the slot, then
the symbol FALSE is returned. A multifield of length zero is returned if an error occurs.
Syntax
(deftemplate-slot-allowed-values <deftemplate-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS>
(deftemplate A
(slot x)
(slot y (allowed-integers 2 3) (allowed-symbols foo)))
CLIPS> (deftemplate-slot-allowed-values A x)
FALSE
CLIPS> (deftemplate-slot-allowed-values A y)
(2 3 foo)
CLIPS>
12.8.3 Getting the Cardinality for a Deftemplate Slot
This function groups the minimum and maximum cardinality allowed for a multifield slot into a
multifield variable. A maximum cardinality of infinity is indicated by the symbol +oo (the plus
character followed by two lowercase o’s—not zeroes). A multifield of length zero is returned for
single field slots or if an error occurs.
Syntax
(deftemplate-slot-cardinality <deftemplate-name> <slot-name>)
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Example
CLIPS> (clear)
CLIPS>
(deftemplate A
(slot x)
(multislot y (cardinality ?VARIABLE 5))
(multislot z (cardinality 3 ?VARIABLE)))
CLIPS> (deftemplate-slot-cardinality A y)
(0 5)
CLIPS> (deftemplate-slot-cardinality A z)
(3 +oo)
CLIPS>
12.8.4 Testing whether a Deftemplate Slot has a Default
This function returns the symbol static if the specified slot in the specified deftemplate has a
static default (whether explicitly or implicitly defined), the symbol dynamic if the slot has a
dynamic default, or the symbol FALSE if the slot does not have a default. An error is generated
if the specified deftemplate or slot does not exist.
Syntax
(deftemplate-slot-defaultp <deftemplate-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS>
(deftemplate A
(slot w)
(slot x (default ?NONE))
(slot y (default 1))
(slot z (default-dynamic (gensym))))
CLIPS> (deftemplate-slot-defaultp A w)
static
CLIPS> (deftemplate-slot-defaultp A x)
FALSE
CLIPS> (deftemplate-slot-defaultp A y)
static
CLIPS> (deftemplate-slot-defaultp A z)
dynamic
CLIPS>
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12.8.5 Getting the Default Value for a Deftemplate Slot
This function returns the default value associated with a deftemplate slot. If a slot has a dynamic
default, the expression will be evaluated when this function is called. The symbol FALSE is
returned if an error occurs.
Syntax
(deftemplate-slot-default-value <deftemplate-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS>
(deftemplate A
(slot x (default 3))
(multislot y (default a b c))
(slot z (default-dynamic (gensym))))
CLIPS> (deftemplate-slot-default-value A x)
3
CLIPS> (deftemplate-slot-default-value A y)
(a b c)
CLIPS> (deftemplate-slot-default-value A z)
gen1
CLIPS> (deftemplate-slot-default-value A z)
gen2
CLIPS>
12.8.6 Deftemplate Slot Existence
This function returns the symbol TRUE if the specified slot is present in the specified
deftemplate, FALSE otherwise.
Syntax
(deftemplate-slot-existp <deftemplate-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS> (deftemplate A (slot x))
CLIPS> (deftemplate-slot-existp A x)
TRUE
CLIPS> (deftemplate-slot-existp A y)
FALSE
CLIPS>
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12.8.7 Testing whether a Deftemplate Slot is a Multifield Slot
This function returns the symbol TRUE if the specified slot in the specified deftemplate is a
multifield slot. Otherwise, it returns the symbol FALSE. An error is generated if the specified
deftemplate or slot does not exist.
Syntax
(deftemplate-slot-multip <deftemplate-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS> (deftemplate A (slot x) (multislot y))
CLIPS> (deftemplate-slot-multip A x)
FALSE
CLIPS> (deftemplate-slot-multip A y)
TRUE
CLIPS>
12.8.8 Determining the Slot Names Associated with a Deftemplate
The deftemplate-slot-names function returns the slot names associated with the deftemplate in a
multifield value. The symbol implied is returned for an implied deftemplate (which has a single
implied multifield slot). FALSE is returned if the specified deftemplate does not exist.
Syntax
(deftemplate-slot-names <deftemplate-name>)
Example
CLIPS> (clear)
CLIPS> (deftemplate foo (slot bar) (multislot yak))
CLIPS> (deftemplate-slot-names foo)
(bar yak)
CLIPS>
12.8.9 Getting the Numeric Range for a Deftemplate Slot
This function groups the minimum and maximum numeric ranges allowed a slot into a multifield
variable. A minimum value of infinity is indicated by the symbol -oo (the minus character
followed by two lowercase o’s—not zeroes). A maximum value of infinity is indicated by the
symbol +oo (the plus character followed by two lowercase o’s—not zeroes). The symbol FALSE
is returned for slots in which numeric values are not allowed. A multifield of length zero is
returned if an error occurs.
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Syntax
(deftemplate-slot-range <deftemplate-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS>
(deftemplate A
(slot x)
(slot y (type SYMBOL))
(slot z (range 3 10)))
CLIPS> (deftemplate-slot-range A x)
(-oo +oo)
CLIPS> (deftemplate-slot-range A y)
FALSE
CLIPS> (deftemplate-slot-range A z)
(3 10)
CLIPS>
12.8.10 Testing whether a Deftemplate Slot is a Single-Field Slot
This function returns the symbol TRUE if the specified slot in the specified deftemplate is a
single-field slot. Otherwise, it returns the symbol FALSE. An error is generated if the specified
deftemplate or slot does not exist.
Syntax
(deftemplate-slot-singlep <deftemplate-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS> (deftemplate A (slot x) (multislot y))
CLIPS> (deftemplate-slot-singlep A x)
TRUE
CLIPS> (deftemplate-slot-singlep A y)
FALSE
CLIPS>
12.8.11 Getting the Primitive Types for a Deftemplate Slot
This function groups the names of the primitive types allowed for a deftemplate slot into a
multifield variable. A multifield of length zero is returned if an error occurs.
Syntax
(deftemplate-slot-types <deftemplate-name> <slot-name>)
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Example
CLIPS> (clear)
CLIPS> (deftemplate A (slot y (type INTEGER LEXEME)))
CLIPS> (deftemplate-slot-types A y)
(INTEGER SYMBOL STRING)
CLIPS>
12.8.12 Getting the List of Deftemplates
The function get-deftemplate-list returns a multifield value containing the names of all
deftemplate constructs facts visible to the module specified by <module-name> or to the current
module if none is specified. If * is specified as the module name, then all deftemplates are
returned.
Syntax
(get-deftemplate-list [<module-name>])
Example
CLIPS> (clear)
CLIPS> (deftemplate A)
CLIPS> (deftemplate B)
CLIPS> (get-deftemplate-list)
(initial-fact A B)
CLIPS>
12.9 Fact Functions
The following actions are used for assert, retracting, and modifying facts.
12.9.1 Creating New Facts
The assert action allows the user to add a fact to the fact-list. Multiple facts may be asserted with
each call. If the facts item is being watched (see section 13.2), then an informational message
will be printed each time a fact is asserted.
Syntax
(assert <RHS-pattern>+)
Missing slots in a template fact being asserted are assigned their default value (see section 3). If
an identical copy of the fact already exists in the fact-list, the fact will not be added (however,
this behavior can be changed, see sections 13.4.4 and 13.4.5). Note that in addition to constants,
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expressions can be placed within a fact to be asserted. The first field of a fact must be a symbol.
The value returned of the assert function is the fact-address of the last fact asserted. If the
assertion of the last fact causes an error, or if an identical copy of the fact already exists in the
fact-list, then the symbol FALSE is returned.
Example
CLIPS> (clear)
CLIPS> (assert (color red))
<Fact-1>
CLIPS> (assert (color blue) (value (+ 3 4)))
<Fact-3>
CLIPS> (assert (color red))
FALSE
CLIPS> (deftemplate status (slot temp) (slot pressure))
CLIPS> (assert (status (temp high)
(pressure low)))
<Fact-4>
CLIPS> (facts)
f-0 (initial-fact)
f-1 (color red)
f-2 (color blue)
f-3 (value 7)
f-4 (status (temp high) (pressure low))
For a total of 5 facts.
CLIPS>
12.9.2 Removing Facts from the Fact-list
The retract action allows the user to remove facts from the fact-list. Multiple facts may be
retracted with a single retract statement. The retraction of a fact also removes all rules that
depended upon that fact for activation from the agenda. Retraction of a fact may also cause the
retraction of other facts which receive logical support from the retracted fact. If the facts item is
being watched (see section 13.2), then an informational message will be printed each time a fact
is retracted.
Syntax
(retract <retract-specifier>+ | *)
<retract-specifier> ::= <fact-specifier> | <integer-expression>
The term <retract-specifier> includes variables bound on the LHS to fact-addresses as described
in section 5.4.1.8, or the fact-index of the desired fact (e.g. 3 for the fact labeled f-3), or an
expression which evaluates to a retract-specifier. If the symbol * is used as an argument, all facts
will be retracted. Note that the number generally is not known during the execution of a program,
so facts usually are retracted by binding them on the LHS of a rule. Only variables, fact indices,
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or the symbol * may be used in a retract. External functions may not be called. This function has
no return value.
Example
(defrule change-valve-status
?f1 <- (valve ?v open)
?f2 <- (set ?v close)
=>
(retract ?f1 ?f2)
(assert (valve ?v close)))
12.9.3 Modifying Template Facts
The modify action allows the user to modify template facts on the fact-list. Only one fact may be
modified with a single modify statement. The modification of a fact is equivalent to retracting
the present fact and asserting the modified fact. Therefore, any facts receiving logical support
from a template fact are retracted (assuming no other support) when the template fact is modified
and the new template fact loses any logical support that it previously had.
Syntax
(modify <fact-specifier> <RHS-slot>*)
The term <fact-specifier> includes variables bound on the LHS to fact-addresses as described in
section 5.4.1.8 or the fact-index of the desired fact (e.g. 3 for the fact labeled f-3). Note that the
fact-index generally is not known during the execution of a program, so facts usually are
modified by binding them on the LHS of a rule. Static deftemplate checking is not performed
when a fact-index is used as the <fact-specifier> since the deftemplate being referenced is
usually ambiguous. Only variables or fact indices may be used in a modify. External functions
may not be called. The value returned by this function is the fact-address of the newly modified
fact. If the assertion of the newly modified fact causes an error, or if an identical copy of the
newly modified fact already exists in the fact-list, then the symbol FALSE is returned.
Example
(defrule change-valve-status
?f1<-(status (valve open))
?f2<-(close-valve)
=>
(retract ?f2)
(modify ?f1 (valve closed)))
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12.9.4 Duplicating Template Facts
The duplicate action allows the user to duplicate deftemplate facts on the fact-list changing a
group of specified fields. This command allows a new fact to be created by copying most of the
fields of a source fact and then specifying the fields to be changed. Only one fact may be
duplicated with a single duplicate statement. The duplicate command is similar to the modify
command except the fact being duplicated is not retracted.
Syntax
(duplicate <fact-specifier> <RHS-slot>*)
The term <fact-specifier> includes variables bound on the LHS to fact-addresses as described in
section 5.4.1.8 or the fact-index of the desired fact (e.g. 3 for the fact labeled f-3). Note that the
fact-index generally is not known during the execution of a program, so facts usually are
duplicated by binding them on the LHS of a rule. Static deftemplate checking is not performed
when a fact-index is used as the <fact-specifier> since the deftemplate being referenced is
usually ambiguous. Only variables or fact indices may be used in a duplicate. External functions
may not be called. The value returned by this function is the fact-address of the newly duplicated
fact. If the assertion of the newly duplicated fact causes an error, or if an identical copy of the
newly duplicated fact already exists in the fact-list, then the symbol FALSE is returned.
Example
(defrule duplicate-part
?f1 <- (duplicate-part ?name)
?f2 <- (part (name ?name))
=>
(retract ?f1)
(duplicate ?f2 (id (gensym*))))
12.9.5 Asserting a String
The assert-string function is similar to assert in that it will add a fact to the fact-list. However,
assert-string takes a single string representing a fact (expressed in either ordered or deftemplate
format ) and asserts it. Only one fact may be asserted with each assert-string statement.
Syntax
(assert-string <string-expression>)
If an identical copy of the fact already exists in the fact-list, the fact will not be added (however,
this behavior can be changed, see sections 13.4.4 and 13.4.5). Fields within the fact may contain
a string by escaping the quote character with a backslash. Note that this function takes a string
and turns it into fields. If the fields within that string are going to contain special characters (such
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as a backslash), they need to be escaped twice (because you are literally embedding a string
within a string and the backslash mechanism ends up being applied twice). Global variables and
expressions can be contained within the string. The value returned by this function is the
fact-address of the newly created fact. If the assertion of the newly created fact causes an error,
or if an identical copy of the newly created fact already exists in the fact-list, then the symbol
FALSE is returned.
Example
CLIPS> (clear)
CLIPS> (deftemplate foo (slot x) (slot y))
CLIPS> (assert-string "(status valve open)")
<Fact-1>
CLIPS> (assert-string "(light \"red\")")
<Fact-2>
CLIPS> (assert-string "(a\\b \"c\\\\d\")")
<Fact-3>
CLIPS> (assert-string "(foo (x 3))")
<Fact-4>
CLIPS> (assert-string "(foo (y 7))")
<Fact-5>
CLIPS> (facts)
f-0 (initial-fact)
f-1 (status valve open)
f-2 (light "red")
f-3 (a\b "c\d")
f-4 (foo (x 3) (y nil))
f-5 (foo (x nil) (y 7))
For a total of 6 facts.
CLIPS>
12.9.6 Getting the Fact-Index of a Fact-address
The fact-index function returns the fact-index (an integer) of a fact-address.
Syntax
(fact-index <fact-address>)
Example
(defrule print-fact-indices
?f <- (some-fact $?)
=>
(printout t (fact-index ?f) crlf))
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12.9.7 Determining If a Fact Exists
The fact-existp returns TRUE if the fact specified by its fact-index or fact-address arguments
exists, otherwise FALSE is returned.
Syntax
(fact-existp <fact-address-or-index>)
Example
CLIPS> (clear)
CLIPS> (defglobal ?*x* = (assert (example fact)))
CLIPS> (facts)
f-0 (initial-fact)
f-1 (example fact)
For a total of 2 facts.
CLIPS> (fact-existp 1)
TRUE
CLIPS> (retract 1)
CLIPS> (fact-existp ?*x*)
FALSE
CLIPS>
12.9.8 Determining the Deftemplate (Relation) Name Associated with a Fact
The fact-relation function returns the deftemplate (relation) name associated with the fact.
FALSE is returned if the specified fact does not exist.
Syntax
(fact-relation <fact-address-or-index>)
Example
CLIPS> (clear)
CLIPS> (assert (example fact))
<Fact-1>
CLIPS> (fact-relation 1)
example
CLIPS>
12.9.9 Determining the Slot Names Associated with a Fact
The fact-slot-names function returns the slot names associated with the fact in a multifield
value. The symbol implied is returned for an ordered fact (which has a single implied multifield
slot). FALSE is returned if the specified fact does not exist.
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Syntax
(fact-slot-names <fact-address-or-index>)
Example
CLIPS> (clear)
CLIPS> (deftemplate foo (slot bar) (multislot yak))
CLIPS> (assert (foo (bar 1) (yak 2 3)))
<Fact-1>
CLIPS> (fact-slot-names 1)
(bar yak)
CLIPS> (assert (another a b c))
<Fact-2>
CLIPS> (fact-slot-names 2)
(implied)
CLIPS>
12.9.10 Retrieving the Slot Value of a Fact
The fact-slot-value function returns the value of the specified slot from the specified fact. The
symbol implied should be used as the slot name for the implied multifield slot of an ordered fact.
FALSE is returned if the slot name argument is invalid or the specified fact does not exist.
Syntax
(fact-slot-value <fact-address-or-index> <slot-name>)
Example
CLIPS> (clear)
CLIPS> (deftemplate foo (slot bar) (multislot yak))
CLIPS> (assert (foo (bar 1) (yak 2 3)))
<Fact-1>
CLIPS> (fact-slot-value 1 bar)
1
CLIPS> (fact-slot-value 1 yak)
(2 3)
CLIPS> (assert (another a b c))
<Fact-2>
CLIPS> (fact-slot-value 2 implied)
(a b c)
CLIPS>
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12.9.11 Retrieving the Fact-List
The get-fact-list function returns a multifield containing the list of facts visible to the module
specified by <module-name> or to the current module if none is specified. If * is specified as the
module name, then all facts are returned.
Syntax
(get-fact-list [<module-name>])
Example
CLIPS> (clear)
CLIPS> (assert (a))
<Fact-1>
CLIPS> (get-fact-list)
(<Fact-0> <Fact-1>)
CLIPS> (defmodule B)
CLIPS> (assert (b))
<Fact-2>
CLIPS> (get-fact-list)
(<Fact-2>)
CLIPS> (get-fact-list MAIN)
(<Fact-0> <Fact-1>)
CLIPS> (get-fact-list *)
(<Fact-0> <Fact-1> <Fact-2>)
CLIPS>
12.9.12 Fact-set Queries and Distributed Actions
CLIPS provides a useful query system for determining and performing actions on sets of facts
that satisfy user-defined queries. The fact query system in CLIPS provides six functions, each of
which operate on fact-sets determined by user-defined criteria:
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Function
Purpose
any-factp
Determines if one or more fact-sets
satisfy a query
find-fact
Returns the first fact-set that satisfies a
query
find-all-facts
Groups and returns all fact-sets which
satisfy a query
do-for-fact
Performs an action for the first fact-set
which satisfies a query
do-for-all-facts
Performs an action for every fact-set
which satisfies a query as they are found
delayed-do-for-all-facts
Groups all fact-sets which satisfy a query
and then iterates an action over this group
Explanations on how to form fact-set templates, queries and actions immediately follow, for
these definitions are common to all of the query functions. The specific details of each query
function will then be given. The following is a complete example of a fact-set query function:
Example
For all of the examples in this section, assume that the commands below have already been
entered:
Example
CLIPS> (clear)
CLIPS>
(deftemplate girl
(slot name)
(slot sex (default female))
(slot age (default 4)))
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CLIPS>
(deftemplate woman
(slot name)
(slot sex (default female))
(slot age (default 25)))
CLIPS>
(deftemplate boy
(slot name)
(slot sex (default male))
(slot age (default 4)))
CLIPS>
(deftemplate man
(slot name)
(slot sex (default male))
(slot age (default 25)))
CLIPS>
(deffacts PEOPLE
(man (name Man-1) (age 18))
(man (name Man-2) (age 60))
(woman (name Woman-1) (age 18))
(woman (name Woman-2) (age 60))
(woman (name Woman-3))
(boy (name Boy-1) (age 8))
(boy (name Boy-2))
(boy (name Boy-3))
(boy (name Boy-4))
(girl (name Girl-1) (age 8))
(girl (name Girl-2)))
CLIPS> (reset)
CLIPS> (facts)
f-0 (initial-fact)
f-1 (man (name Man-1) (sex male) (age 18))
f-2 (man (name Man-2) (sex male) (age 60))
f-3 (woman (name Woman-1) (sex female) (age 18))
f-4 (woman (name Woman-2) (sex female) (age 60))
f-5 (woman (name Woman-3) (sex female) (age 25))
f-6 (boy (name Boy-1) (sex male) (age 8))
f-7 (boy (name Boy-2) (sex male) (age 4))
f-8 (boy (name Boy-3) (sex male) (age 4))
f-9 (boy (name Boy-4) (sex male) (age 4))
f-10 (girl (name Girl-1) (sex female) (age 8))
f-11 (girl (name Girl-2) (sex female) (age 4))
For a total of 12 facts.
CLIPS>
12.9.12.1 Fact-set Definition
A fact-set is an ordered collection of facts. Each fact-set member is a member of a set of
deftemplates, called template restrictions, defined by the user. The template restrictions can be
different for each fact-set member. The query functions use fact-set templates to generate
fact-sets. A fact-set template is a set of fact-set member variables and their associated template
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restrictions. Fact-set member variables reference the corresponding members in each fact-set
which matches a template. Variables may be used to specify the deftemplates for the fact-set
template, but if the constant names of the deftemplates are specified, the deftemplates must
already be defined. Module specifiers may be included with the deftemplate names; the
deftemplates need not be in scope of the current module.
Syntax
<fact-set-template>
::= (<fact-set-member-template>+)
<fact-set-member-template>
::= (<fact-set-member-variable> <deftemplate-restrictions>)
<fact-set-member-variable> ::= <single-field-variable>
<deftemplate-restrictions> ::= <deftemplate-name-expression>+
Example
One fact-set template might be the ordered pairs of boys or men and girls or women.
((?man-or-boy boy man) (?woman-or-girl girl woman))
Fact-set member variables (e.g. ?man-or-boy) are bound to fact-addresses.
12.9.12.2 Fact-set Determination
CLIPS uses straightforward permutations to generate fact-sets that match a fact-set template
from the actual facts in the system. The rules are as follows:
1) When there is more than one member in a fact-set template, vary the rightmost members
first.
2) When there is more than one deftemplate that an fact-set member can be, iterate through the
deftemplate from left to right.
3) Examine facts of a deftemplate in the order that they were defined.
Example
For the fact-set template given in section 12.9.12.1, thirty fact-sets would be generated in the
following order:
1. <Fact-6> <Fact-10>
2. <Fact-6> <Fact-11>
3. <Fact-6> <Fact-3>
4. .<Fact-6> <Fact-4>
5. <Fact-6> <Fact-5>
16. <Fact-9> <Fact-10>
17. <Fact-9> <Fact-11>
18. <Fact-9> <Fact-3>
19. <Fact-9> <Fact-4>
20. <Fact-9> <Fact-5>
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6. <Fact-7> <Fact-10>
7. <Fact-7> <Fact-11>
8. <Fact-7> <Fact-3>
9. <Fact-7> <Fact-4>
10. <Fact-7> <Fact-5>
11. <Fact-8> <Fact-10>
12. <Fact-8> <Fact-11>
13 <Fact-8> <Fact-3>
14. <Fact-8> <Fact-4>
15. <Fact-8> <Fact-5>
21. <Fact-1> <Fact-10>
22. <Fact-1> <Fact-11>
23. <Fact-1> <Fact-3>
24. <Fact-1> <Fact-4>
25. <Fact-1> <Fact-5>
26. <Fact-2> <Fact-10>
27. <Fact-2> <Fact-11>
28. <Fact-2> <Fact-3>
29. <Fact-2> <Fact-4>
30. <Fact-2> <Fact-5>
12.9.12.3 Query Definition
A query is a user-defined boolean expression applied to a fact-set to determine if the fact-set
meets further user-defined restrictions. If the evaluation of this expression for an fact-set is
anything but the symbol FALSE, the fact-set is said to satisfy the query.
Syntax
<query> ::= <boolean-expression>
Example
Continuing the previous example, one query might be that the two facts in an ordered pair have
the same age.
(= (fact-slot-value ?man-or-boy age) (fact-slot-value ?woman-or-girl age))
Within a query, slots of fact-set members can be directly read with a shorthand notation similar
to that used by instances in message-handlers (see section 9.4.2).
Syntax
<fact-set-member-variable>:<slot-name>
Example
The previous example could be rewritten as:
(= ?man-or-boy:age ?woman-or-girl:age)
Since only fact-sets which satisfy a query are of interest, and the query is evaluated for all
possible fact-sets, the query should not have any side-effects.
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12.9.12.4 Distributed Action Definition
A distributed action is a user-defined expression evaluated for each fact-set which satisfies a
query.
Action Syntax
<action> ::= <expression>
Example
Continuing the previous example, one distributed action might be to simply print out the ordered
pair to the screen.
(printout t "(" ?man-or-boy:name "," ?woman-or-girl:name ")" crlf)
12.9.12.5 Scope in Fact-set Query Functions
A fact-set query function can be called from anywhere that a regular function can be called. If a
variable from an outer scope is not masked by a fact-set member variable, then that variable may
be referenced within the query and action. In addition, rebinding variables within a fact-set
function action is allowed. However, attempts to rebind fact-set member variables will generate
errors. Binding variables is not allowed within a query. Fact-set query functions can be nested.
Example
CLIPS>
(deffunction count-facts (?template)
(bind ?count 0)
(do-for-all-facts ((?fct ?template)) TRUE
(bind ?count (+ ?count 1)))
?count)
CLIPS>
(deffunction count-facts-2 (?template)
(length (find-all-facts ((?fct ?template)) TRUE)))
CLIPS> (count-facts woman)
3
CLIPS> (count-facts-2 boy)
4
CLIPS>
Fact-set member variables are only in scope within the fact-set query function. Attempting to
use fact-set member variables in an outer scope will generate an error.
Example
CLIPS>
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(deffunction last-fact (?template)
(any-factp ((?fct ?template)) TRUE)
?fct)
[PRCCODE3] Undefined variable fct referenced in deffunction.
ERROR:
(deffunction MAIN::last-fact
(?template)
(any-factp ((?fct ?template))
TRUE)
?fct
)
CLIPS>
12.9.12.6 Errors during Instance-set Query Functions
If an error occurs during an fact-set query function, the function will be immediately terminated
and the return value will be the symbol FALSE.
12.9.12.7 Halting and Returning Values from Query Functions
The functions break and return are now valid inside the action of the fact-set query functions
do-for-fact, do-for-all-facts and delayed-do-for-all-facts. The return function is only valid if it
is applicable in the outer scope, whereas the break function actually halts the query.
12.9.12.8 Fact-set Query Functions
The fact query system in CLIPS provides six functions. For a given set of facts, all six query
functions will iterate over these facts in the same order (see section 12.9.12.2). However, if a
particular fact is retracted and reasserted, the iteration order will change.
12.9.12.8.1 Testing if Any Fact-set Satisfies a Query
This function applies a query to each fact-set which matches the template. If a fact-set satisfies
the query, then the function is immediately terminated, and the return value is the symbol TRUE.
Otherwise, the return value is the symbol FALSE.
Syntax
(any-factp <fact-set-template> <query>)
Example
Are there any men over age 30?
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CLIPS> (any-factp ((?man man)) (> ?man:age 30))
TRUE
CLIPS>
12.9.12.8.2 Determining the First Fact-set Satisfying a Query
This function applies a query to each fact-set which matches the template. If a fact-set satisfies
the query, then the function is immediately terminated, and the fact-set is returned in a multifield
value. Otherwise, the return value is a zero-length multifield value. Each field of the multifield
value is a fact-address representing a fact-set member.
Syntax
(find-fact <fact-set-template> <query>)
Example
Find the first pair of a man and a woman who have the same age.
CLIPS>
(find-fact((?m man) (?w woman)) (= ?m:age ?w:age))
(<Fact-1> <Fact-3>)
CLIPS>
12.9.12.8.3 Determining All Fact-sets Satisfying a Query
This function applies a query to each fact-set which matches the template. Each fact-set which
satisfies the query is stored in a multifield value. This multifield value is returned when the query
has been applied to all possible fact-sets. If there are n facts in each fact-set, and m fact-sets
satisfied the query, then the length of the returned multifield value will be n * m. The first n
fields correspond to the first fact-set, and so on. Each field of the multifield value is an
fact-address representing a fact-set member. The multifield value can consume a large amount of
memory due to permutational explosion, so this function should be used judiciously.
Syntax
(find-all-facts <fact-set-template> <query>)
Example
Find all pairs of a man and a woman who have the same age.
CLIPS>
(find-all-facts ((?m man) (?w woman)) (= ?m:age ?w:age))
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(<Fact-1> <Fact-3> <Fact-2> <Fact-4>)
CLIPS>
12.9.12.8.4 Executing an Action for the First Fact-set Satisfying a Query
This function applies a query to each fact-set which matches the template. If a fact-set satisfies
the query, the specified action is executed, and the function is immediately terminated. The
return value is the evaluation of the action. If no fact-set satisfied the query, then the return value
is the symbol FALSE.
Syntax
(do-for-fact <fact-set-template> <query> <action>*)
Example
Print out the first triplet of different people that have the same age. The calls to neq in the query
eliminate the permutations where two or more members of the instance-set are identical.
CLIPS>
(do-for-fact ((?p1 girl boy woman man)
(?p2 girl boy woman man)
(?p3 girl boy woman man))
(and (= ?p1:age ?p2:age ?p3:age)
(neq ?p1 ?p2)
(neq ?p1 ?p3)
(neq ?p2 ?p3))
(printout t ?p1:name " " ?p2:name " " ?p3:name crlf))
Girl-2 Boy-2 Boy-3
CLIPS>
12.9.12.8.5 Executing an Action for All Fact-sets Satisfying a Query
This function applies a query to each fact-set which matches the template. If a fact-set satisfies
the query, the specified action is executed. The return value is the evaluation of the action for the
last fact-set which satisfied the query. If no fact-set satisfied the query, then the return value is
the symbol FALSE.
Syntax
(do-for-all-facts <fact-set-template> <query> <action>*)
Example
Print out all triplets of different people that have the same age. The calls to str-compare limit the
fact-sets which satisfy the query to combinations instead of permutations. Without these
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restrictions, two fact-sets which differed only in the order of their members would both satisfy
the query.
CLIPS>
(do-for-all-facts ((?p1 girl boy woman man)
(?p2 girl boy woman man)
(?p3 girl boy woman man))
(and (= ?p1:age ?p2:age ?p3:age)
(> (str-compare ?p1:name ?p2:name) 0)
(> (str-compare ?p2:name ?p3:name) 0))
(printout t ?p1:name " " ?p2:name " " ?p3:name crlf))
Girl-2 Boy-3 Boy-2
Girl-2 Boy-4 Boy-2
Girl-2 Boy-4 Boy-3
Boy-4 Boy-3 Boy-2
CLIPS>
12.9.12.8.6 Executing a Delayed Action for All Fact-sets Satisfying a Query
This function is similar to do-for-all-facts except that it groups all fact-sets which satisfy the
query into an intermediary multifield value. If there are no fact-sets which satisfy the query, then
the function returns the symbol FALSE. Otherwise, the specified action is executed for each
fact-set in the multifield value, and the return value is the evaluation of the action for the last
fact-set to satisfy the query. The intermediary multifield value is discarded. This function can
consume large amounts of memory in the same fashion as find-all-facts. This function should be
used in lieu of do-for-all-facts when the action applied to one fact-set would change the result of
the query for another fact-set (unless that is the desired effect).
Syntax
(delayed-do-for-all-facts <fact-set-template>
<query> <action>*)
Example
Delete all boys with the greatest age. The test in this case is another query function which
determines if there are any older boys than the one currently being examined. The action needs
to be delayed until all boys have been processed, or the greatest age will decrease as the older
boys are deleted.
CLIPS> (watch facts)
CLIPS>
(delayed-do-for-all-facts ((?b1 boy))
(not (any-factp ((?b2 boy)) (> ?b2:age ?b1:age)))
(retract ?b1))
<== f-6 (boy (name Boy-1) (sex male) (age 8))
CLIPS> (unwatch facts)
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CLIPS> (reset)
CLIPS> (watch facts)
CLIPS>
(do-for-all-facts ((?b1 boy))
(not (any-factp ((?b2 boy)) (> ?b2:age ?b1:age)))
(retract ?b1))
<== f-6 (boy (name Boy-1) (sex male) (age 8))
<== f-7 (boy (name Boy-2) (sex male) (age 4))
<== f-8 (boy (name Boy-3) (sex male) (age 4))
<== f-9 (boy (name Boy-4) (sex male) (age 4))
CLIPS> (unwatch facts)
CLIPS>
12.10 Deffacts Functions
The following functions provide ancillary capabilities for the deffacts construct.
12.10.1 Getting the List of Deffacts
The function get-deffacts-list returns a multifield value containing the names of all deffacts
constructs visible to the module specified by <module-name> or to the current module if none is
specified. If * is specified as the module name, then all deffacts are returned.
Syntax
(get-deffacts-list [<module-name>])
Example
CLIPS> (clear)
CLIPS> (get-deffacts-list)
(initial-fact)
CLIPS> (deffacts foo)
CLIPS> (get-deffacts-list)
(initial-fact foo)
CLIPS>
12.10.2 Determining the Module in which a Deffacts is Defined
This function returns the module in which the specified deffacts name is defined.
Syntax
(deffacts-module <deffacts-name>)
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12.11 Defrule Functions
The following functions provide ancillary capabilities for the defrule construct.
12.11.1 Getting the List of Defrules
The function get-defrule-list returns a multifield value containing the names of all defrule
constructs visible to the module specified by <module-name> or to the current module if none is
specified. If * is specified as the module name, then all defrules are returned.
Syntax
(get-defrule-list)
Example
CLIPS> (clear)
CLIPS> (get-defrule-list)
()
CLIPS> (defrule foo =>)
CLIPS> (defrule bar =>)
CLIPS> (get-defrule-list)
(foo bar)
CLIPS>
12.11.2 Determining the Module in which a Defrule is Defined
This function returns the module in which the specified defrule name is defined.
Syntax
(defrule-module <defrule-name>)
12.12 Agenda Functions
The following functions provide ancillary capabilities manipulating the agenda.
12.12.1 Getting the Current Focus
The function get-focus returns the module name of the current focus. If the focus stack is empty,
then the symbol FALSE is returned.
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Syntax
(get-focus)
Example
CLIPS> (clear)
CLIPS> (get-focus)
MAIN
CLIPS> (defmodule A)
CLIPS> (defmodule B)
CLIPS> (focus A B)
TRUE
CLIPS> (get-focus)
A
CLIPS>
12.12.2 Getting the Focus Stack
The function get-focus-stack returns all of the module names in the focus stack as a multifield
value. A multifield value of length zero is returned if the focus stack is empty.
Syntax
(get-focus-stack)
Example
CLIPS> (clear)
CLIPS> (get-focus-stack)
(MAIN)
CLIPS> (clear-focus-stack)
CLIPS> (get-focus-stack)
()
CLIPS> (defmodule A)
CLIPS> (defmodule B)
CLIPS> (focus A B)
TRUE
CLIPS> (get-focus-stack)
(A B)
CLIPS>
12.12.3 Removing the Current Focus from the Focus Stack
The function pop-focus removes the current focus from the focus stack and returns the module
name of the current focus. If the focus stack is empty, then the symbol FALSE is returned.
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Syntax
(pop-focus)
Example
CLIPS> (clear)
CLIPS> (list-focus-stack)
MAIN
CLIPS> (pop-focus)
MAIN
CLIPS> (defmodule A)
CLIPS> (defmodule B)
CLIPS> (focus A B)
TRUE
CLIPS> (list-focus-stack)
A
B
MAIN
CLIPS> (pop-focus)
A
CLIPS> (list-focus-stack)
B
CLIPS>
12.13 Defglobal Functions
The following functions provide ancillary capabilities for the defglobal construct.
12.13.1 Getting the List of Defglobals
The function get-defglobal-list returns a multifield value containing the names of all global
variables visible to the module specified by <module-name> or to the current module if none is
specified. If * is specified as the module name, then all globals are returned.
Syntax
(get-defglobal-list [<module-name>])
Example
CLIPS> (clear)
CLIPS> (get-defglobal-list)
()
CLIPS> (defglobal ?*x* = 3 ?*y* = 5)
CLIPS> (get-defglobal-list)
(x y)
CLIPS>
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12.13.2 Determining the Module in which a Defglobal is Defined
This function returns the module in which the specified defglobal name is defined.
Syntax
(defglobal-module <defglobal-name>)
12.14 Deffunction Functions
The following functions provide ancillary capabilities for the deffunction construct.
12.14.1 Getting the List of Deffunctions
The function get-deffunction-list returns a multifield value containing the names of all
deffunction constructs visible to the module specified by <module-name> or to the current
module if none is specified. If * is specified as the module name, then all deffunctions are
returned.
Syntax
(get-deffunction-list [<module-name>])
Example
CLIPS> (clear)
CLIPS> (get-deffunction-list)
()
CLIPS> (deffunction foo ())
CLIPS> (deffunction bar ())
CLIPS> (get-deffunction-list)
(foo bar)
CLIPS>
12.14.2 Determining the Module in which a Deffunction is Defined
This function returns the module in which the specified deffunction name is defined.
Syntax
(deffunction-module <deffunction-name>)
12.15 Generic Function Functions
The following functions provide ancillary capabilities for generic function methods.
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12.15.1 Getting the List of Defgenerics
The function get-defgeneric-list returns a multifield value containing the names of all defgeneric
constructs that are currently defined.
Syntax
(get-defgeneric-list)
Example
CLIPS> (clear)
CLIPS> (get-defgeneric-list)
()
CLIPS> (defgeneric foo)
CLIPS> (defgeneric bar)
CLIPS> (get-defgeneric-list)
(foo bar)
CLIPS>
12.15.2 Determining the Module in which a Generic Function is Defined
This function returns the module in which the specified defgeneric name is defined.
Syntax
(defgeneric-module <defgeneric-name>)
12.15.3 Getting the List of Defmethods
The function get-defmethod-list returns a multifield value containing method name/indices pairs
for all defmethod constructs that are currently defined. The optional generic-function name
parameter restricts the methods return to only those of the specified generic function.
Syntax
(get-defmethod-list [<generic-function-name>])
Example
CLIPS> (clear)
CLIPS> (get-defmethod-list)
()
CLIPS> (defmethod foo ((?x STRING)))
CLIPS> (defmethod foo ((?x INTEGER)))
CLIPS> (defmethod bar ((?x STRING)))
CLIPS> (defmethod bar ((?x INTEGER)))
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CLIPS> (get-defmethod-list)
(foo 1 foo 2 bar 1 bar 2)
CLIPS> (get-defmethod-list foo)
(foo 1 foo 2)
CLIPS>
12.15.4 Type Determination
The function type returns a symbol which is the name of the type (or class) of its of argument.
This function is equivalent to the class function (see section 12.16.4.4), but, unlike the class
function, it is available even when COOL is not installed.
Syntax
(type <expression>)
Example
CLIPS> (type (+ 2 2))
INTEGER
CLIPS> (defclass CAR (is-a USER))
CLIPS> (make-instance Rolls-Royce of CAR)
[Rolls-Royce]
CLIPS> (type Rolls-Royce)
SYMBOL
CLIPS> (type [Rolls-Royce])
CAR
CLIPS>
12.15.5 Existence of Shadowed Methods
If called from a method for a generic function, the function next-methodp will return the symbol
TRUE if there is another method shadowed (see section 8.5.3) by the current one. Otherwise, the
function will return the symbol FALSE.
Syntax
(next-methodp)
12.15.6 Calling Shadowed Methods
If the conditions are such that the function next-methodp would return the symbol TRUE (see
section 12.15.5), then calling the function call-next-method will execute the shadowed (see
section 8.5.3) method. Otherwise, a method execution error will occur (see section 8.5.4). In the
event of an error, the return value of this function is the symbol FALSE, otherwise it is the return
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value of the shadowed method. The shadowed method is passed the same arguments as the
calling method.
A method may continue execution after calling call-next-method. In addition, a method may
make multiple calls to call-next-method, and the same shadowed method will be executed each
time.
Syntax
(call-next-method)
Example
CLIPS>
(defmethod describe ((?a INTEGER))
(if (next-methodp) then
(bind ?extension (str-cat " " (call-next-method)))
else
(bind ?extension ""))
(str-cat "INTEGER" ?extension))
CLIPS> (describe 3)
"INTEGER"
CLIPS>
(defmethod describe ((?a NUMBER))
"NUMBER")
CLIPS> (describe 3)
"INTEGER NUMBER"
CLIPS> (describe 3.0)
"NUMBER"
CLIPS>
12.15.7 Calling Shadowed Methods with Overrides
The function override-next-method is similar to call-next-method, except that new arguments
can be provided. This allows one method to act as a wrapper for another and set up a special
environment for the shadowed method. From the set of methods which are more general than the
currently executing one, the most specific method which is applicable to the new arguments is
executed. (In contrast, call-next-method calls the next most specific method which is applicable
to the same arguments as the currently executing one received.) A recursive call to the generic
function itself should be used in lieu of override-next-method if the most specific of all
methods for the generic function which is applicable to the new arguments should be executed.
Syntax
(override-next-method <expression>*)
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Example
CLIPS> (clear)
CLIPS>
(defmethod + ((?a INTEGER) (?b INTEGER))
(override-next-method (* ?a 2) (* ?b 3)))
CLIPS> (list-defmethods +)
+ #2 (INTEGER) (INTEGER)
+ #SYS1 (NUMBER) (NUMBER) ($? NUMBER)
For a total of 2 methods.
CLIPS> (preview-generic + 1 2)
+ #2 (INTEGER) (INTEGER)
+ #SYS1 (NUMBER) (NUMBER) ($? NUMBER)
CLIPS> (watch methods)
CLIPS> (+ 1 2)
MTH >> +:#2 ED:1 (1 2)
MTH >> +:#SYS1 ED:2 (2 6)
MTH << +:#SYS1 ED:2 (2 6)
MTH << +:#2 ED:1 (1 2)
8
CLIPS> (unwatch methods)
CLIPS>
12.15.8 Calling a Specific Method
The function call-specific-method allows the user to call a particular method of a generic
function without regards to method precedence. This allows the user to bypass method
precedence when absolutely necessary. The method must be applicable to the arguments passed.
Shadowed methods can still be called via call-next-method and override-next-method.
Syntax
(call-specific-method <generic-function> <method-index>
<expression>*)
Example
CLIPS> (clear)
CLIPS>
(defmethod + ((?a INTEGER) (?b INTEGER))
(* (- ?a ?b) (- ?b ?a)))
CLIPS> (list-defmethods +)
+ #2 (INTEGER) (INTEGER)
+ #SYS1 (NUMBER) (NUMBER) ($? NUMBER)
For a total of 2 methods.
CLIPS> (preview-generic + 1 2)
+ #2 (INTEGER) (INTEGER)
+ #SYS1 (NUMBER) (NUMBER) ($? NUMBER)
CLIPS> (watch methods)
CLIPS> (+ 1 2)
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MTH >> +:#2 ED:1 (1 2)
MTH << +:#2 ED:1 (1 2)
-1
CLIPS> (call-specific-method + 1 1 2)
MTH >> +:#SYS1 ED:1 (1 2)
MTH << +:#SYS1 ED:1 (1 2)
3
CLIPS> (unwatch methods)
CLIPS>
12.15.9 Getting the Restrictions of Defmethods
The function get-method-restrictions returns a multifield value containing information about
the restrictions for the specified method using the following format:
<minimum-number-of-arguments>
<maximum-number-of-arguments> (can be -1 for wildcards)
<number-of-restrictions>
<multifield-index-of-first-restriction-info>
.
.
.
<multifield-index-of-nth-restriction-info>
<first-restriction-query> (TRUE or FALSE)
<first-restriction-class-count>
<first-restriction-first-class>
.
.
.
<first-restriction-nth-class>
.
.
.
<mth-restriction-class-count>
<mth-restriction-first-class>
.
.
.
<mth-restriction-nth-class>
Syntax
(get-method-restrictions <generic-function-name>
<method-index>)
Example
CLIPS> (clear)
CLIPS>
(defmethod foo 50 ((?a INTEGER SYMBOL) (?b (= 1 1)) $?c))
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CLIPS> (get-method-restrictions foo 50)
(2 -1 3 7 11 13 FALSE 2 INTEGER SYMBOL TRUE 0 FALSE 0)
CLIPS>
12.16 CLIPS Object-Oriented Language (COOL) Functions
The following functions provide ancillary capabilities for COOL.
12.16.1 Class Functions
12.16.1.1 Getting the List of Defclasses
The function get-defclass-list returns a multifield value containing the names of all defclass
constructs visible to the module specified by <module-name> or to the current module if none is
specified. If * is specified as the module name, then all defclasses are returned.
Syntax
(get-defclass-list [<module-name>])
Example
CLIPS> (clear)
CLIPS> (get-defclass-list)
(FLOAT INTEGER SYMBOL STRING MULTIFIELD EXTERNAL-ADDRESS FACT-ADDRESS INSTANCE-
ADDRESS INSTANCE-NAME OBJECT PRIMITIVE NUMBER LEXEME ADDRESS INSTANCE USER
INITIAL-OBJECT)
CLIPS> (defclass FOO (is-a USER))
CLIPS> (defclass BAR (is-a USER))
CLIPS> (get-defclass-list)
(FLOAT INTEGER SYMBOL STRING MULTIFIELD EXTERNAL-ADDRESS FACT-ADDRESS INSTANCE-
ADDRESS INSTANCE-NAME OBJECT PRIMITIVE NUMBER LEXEME ADDRESS INSTANCE USER
INITIAL-OBJECT FOO BAR)
CLIPS>
12.16.1.2 Determining the Module in which a Defclass is Defined
This function returns the module in which the specified defclass name is defined.
Syntax
(defclass-module <defclass-name>)
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12.16.1.3 Determining if a Class Exists
This function returns the symbol TRUE if the specified class is defined, FALSE otherwise.
Syntax
(class-existp <class-name>)
12.16.1.4 Superclass Determination
This function returns the symbol TRUE if the first class is a superclass of the second class,
FALSE otherwise.
Syntax
(superclassp <class1-name> <class2-name>)
12.16.1.5 Subclass Determination
This function returns the symbol TRUE if the first class is a subclass of the second class, FALSE
otherwise.
Syntax
(subclassp <class1-name> <class2-name>)
12.16.1.6 Slot Existence
This function returns the symbol TRUE if the specified slot is present in the specified class,
FALSE otherwise. If the inherit keyword is specified then the slot may be inherited, otherwise it
must be directly defined in the specified class.
Syntax
(slot-existp <class> <slot> [inherit])
12.16.1.7 Testing whether a Slot is Writable
This function returns the symbol TRUE if the specified slot in the specified class is writable (see
section 9.3.3.4). Otherwise, it returns the symbol FALSE. An error is generated if the specified
class or slot does not exist.
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Syntax
(slot-writablep <class-expression> <slot-name-expression>)
12.16.1.8 Testing whether a Slot is Initializable
This function returns the symbol TRUE if the specified slot in the specified class is initializable
(see section 9.3.3.4). Otherwise, it returns the symbol FALSE. An error is generated if the
specified class or slot does not exist.
Syntax
(slot-initablep <class-expression> <slot-name-expression>)
12.16.1.9 Testing whether a Slot is Public
This function returns the symbol TRUE if the specified slot in the specified class is public (see
section 9.3.3.8). Otherwise, it returns the symbol FALSE. An error is generated if the specified
class or slot does not exist.
Syntax
(slot-publicp <class-expression> <slot-name-expression>)
12.16.1.10 Testing whether a Slot can be Accessed Directly
This function returns the symbol TRUE if the specified slot in the specified class can be accessed
directly (see section 9.4.2). Otherwise, it returns the symbol FALSE. An error is generated if the
specified class or slot does not exist.
Syntax
(slot-direct-accessp <class-expression> <slot-name-expression>)
12.16.1.11 Message-handler Existence
This function returns the symbol TRUE if the specified message-handler is defined (directly
only, not by inheritance) for the class, FALSE otherwise.
Syntax
Defaults are in bold italics.
(message-handler-existp <class-name> <handler-name> [<handler-type>])
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<handler-type> ::= around | before |
primary
| after
12.16.1.12 Determining if a Class can have Direct Instances
This function returns the symbol TRUE if the specified class is abstract, i.e. the class cannot
have direct instances, FALSE otherwise.
Syntax
(class-abstractp <class-name>)
12.16.1.13 Determining if a Class can Satisfy Object Patterns
This function returns the symbol TRUE if the specified class is reactive, i.e. objects of the class
can match object patterns, FALSE otherwise.
Syntax
(class-reactivep <class-name>)
12.16.1.14 Getting the List of Superclasses for a Class
This function groups the names of the direct superclasses of a class into a multifield variable. If
the optional argument “inherit” is given, indirect superclasses are also included. A multifield of
length zero is returned if an error occurs.
Syntax
(class-superclasses <class-name> [inherit])
Example
CLIPS> (class-superclasses INTEGER)
(NUMBER)
CLIPS> (class-superclasses INTEGER inherit)
(NUMBER PRIMITIVE OBJECT)
CLIPS>
12.16.1.15 Getting the List of Subclasses for a Class
This function groups the names of the direct subclasses of a class into a multifield variable. If the
optional argument “inherit” is given, indirect subclasses are also included. A multifield of length
zero is returned if an error occurs.
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Syntax
(class-subclasses <class-name> [inherit])
Example
CLIPS> (class-subclasses PRIMITIVE)
(NUMBER LEXEME MULTIFIELD ADDRESS INSTANCE)
CLIPS> (class-subclasses PRIMITIVE inherit)
(NUMBER INTEGER FLOAT LEXEME SYMBOL STRING MULTIFIELD ADDRESS EXTERNAL-ADDRESS
FACT-ADDRESS INSTANCE-ADDRESS INSTANCE INSTANCE-NAME)
CLIPS>
12.16.1.16 Getting the List of Slots for a Class
This function groups the names of the explicitly defined slots of a class into a multifield variable.
If the optional argument “inherit” is given, inherited slots are also included. A multifield of
length zero is returned if an error occurs.
Syntax
(class-slots <class-name> [inherit])
Example
CLIPS> (defclass A (is-a USER) (slot x))
CLIPS> (defclass B (is-a A) (slot y))
CLIPS> (class-slots B)
(y)
CLIPS> (class-slots B inherit)
(x y)
CLIPS>
12.16.1.17 Getting the List of Message-Handlers for a Class
This function groups the class names, message names and message types of the
message-handlers attached direct to class into a multifield variable (implicit slot-accessors are
not included). If the optional argument “inherit” is given, inherited message-handlers are also
included. A multifield of length zero is returned if an error occurs.
Syntax
(get-defmessage-handler-list <class-name> [inherit])
Example
CLIPS> (clear)
CLIPS> (defclass A (is-a USER))
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CLIPS> (defmessage-handler A foo ())
CLIPS> (get-defmessage-handler-list A)
(A foo primary)
CLIPS> (get-defmessage-handler-list A inherit)
(USER init primary USER delete primary USER create primary USER print primary USER
direct-modify primary USER message-modify primary USER direct-duplicate primary
USER message-duplicate primary A foo primary)
CLIPS>
12.16.1.18 Getting the List of Facets for a Slot
This function returns a multifield listing the facet values for the specified slot (the slot can be
inherited or explicitly defined for the class). A multifield of length zero is returned if an error
occurs. Following is a table indicating what each field represents and its possible values:
Field
Meaning
Values
Explanation
1
Field Type
SGL/MLT
Single-field or multifield
2
Default Value
STC/DYN/NIL
Static, dynamic, or none
3
Inheritance
INH/NIL
Inheritable by other classes or not
4
Access
RW/R/INT
Read-write, read-only, or initialize-only
5
Storage
LCL/SHR
Local or shared
6
Pattern-Match
RCT/NIL
Reactive or non-reactive
7
Source
EXC/CMP
Exclusive or composite
8
Visibility
PUB/PRV
Public or private
9
Automatic Accessors
R/W/RW/NIL
Read, write, read-write, or none
10
Override-Message
<message-name>
Name of message sent for slot-overrides
See section 9.3.3 for more details on slot facets.
Syntax
(slot-facets <class-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS> (defclass A (is-a USER) (slot x (access read-only)))
CLIPS> (defclass B (is-a A) (multislot y))
CLIPS> (slot-facets B x)
(SGL STC INH R SHR RCT EXC PRV R NIL)
CLIPS> (slot-facets B y)
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(MLT STC INH RW LCL RCT EXC PRV RW put-y)
CLIPS>>
12.16.1.19 Getting the List of Source Classes for a Slot
This function groups the names of the classes which provide facets for a slot of a class into a
multifield variable. In the case of an exclusive slot, this multifield will be of length one and
contain the name of the contributing class. However, composite slots may have facets from many
different classes (see section 9.3.3.6). A multifield of length zero is returned if an error occurs.
Syntax
(slot-sources <class-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot x (access read-only)))
CLIPS>
(defclass B (is-a A)
(slot x (source composite)
(default 100)))
CLIPS> (defclass C (is-a B))
CLIPS> (slot-sources A x)
(A)
CLIPS> (slot-sources B x)
(A B)
CLIPS> (slot-sources C x)
(A B)
CLIPS>
12.16.1.20 Getting the Primitive Types for a Slot
This function groups the names of the primitive types allowed for a slot into a multifield
variable. A multifield of length zero is returned if an error occurs.
Syntax
(slot-types <class-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS> (defclass A (is-a USER) (slot y (type INTEGER LEXEME)))
CLIPS> (slot-types A y)
(INTEGER SYMBOL STRING)
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CLIPS>
12.16.1.21 Getting the Cardinality for a Slot
This function groups the minimum and maximum cardinality allowed for a multifield slot into a
multifield variable. A maximum cardinality of infinity is indicated by the symbol +oo (the plus
character followed by two lowercase o’s—not zeroes). A multifield of length zero is returned for
single field slots or if an error occurs.
Syntax
(slot-cardinality <class-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot x)
(multislot y (cardinality ?VARIABLE 5))
(multislot z (cardinality 3 ?VARIABLE)))
CLIPS> (slot-cardinality A x)
()
CLIPS> (slot-cardinality A y)
(0 5)
CLIPS> (slot-cardinality A z)
(3 +oo)
CLIPS>
12.16.1.22 Getting the Allowed Values for a Slot
This function groups the allowed values for a slot (specified in any of allowed-… facets for the
slots) into a multifield variable. If no allowed-… facets were specified for the slot, then the
symbol FALSE is returned. A multifield of length zero is returned if an error occurs.
Syntax
(slot-allowed-values <class-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot x)
(slot y (allowed-integers 2 3) (allowed-symbols foo)))
CLIPS> (slot-allowed-values A x)
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FALSE
CLIPS> (slot-allowed-values A y)
(2 3 foo)
CLIPS>
12.16.1.23 Getting the Numeric Range for a Slot
This function groups the minimum and maximum numeric ranges allowed a slot into a multifield
variable. A minimum value of infinity is indicated by the symbol -oo (the minus character
followed by two lowercase o’s—not zeroes). A maximum value of infinity is indicated by the
symbol +oo (the plus character followed by two lowercase o’s—not zeroes). The symbol FALSE
is returned for slots in which numeric values are not allowed. A multifield of length zero is
returned if an error occurs.
Syntax
(slot-range <class-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS>
(defclass A (is-a USER)
(slot x)
(slot y (type SYMBOL))
(slot z (range 3 10)))
CLIPS> (slot-range A x)
(-oo +oo)
CLIPS> (slot-range A y)
FALSE
CLIPS> (slot-range A z)
(3 10)
CLIPS>
12.16.1.24 Getting the Default Value for a Slot
This function returns the default value associated with a slot. If a slot has a dynamic default, the
expression will be evaluated when this function is called. The symbol FALSE is returned if an
error occurs.
Syntax
(slot-default-value <class-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS>
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(defclass A (is-a USER)
(slot x (default 3))
(multislot y (default a b c))
(slot z (default-dynamic (gensym))))
CLIPS> (slot-default-value A x)
3
CLIPS> (slot-default-value A y)
(a b c)
CLIPS> (slot-default-value A z)
gen1
CLIPS> (slot-default-value A z)
gen2
CLIPS>
12.16.1.25 Setting the Defaults Mode for Classes
This function sets the defaults mode used when classes are defined. The old mode is the return
value of this function.
Syntax
(set-class-defaults-mode <mode>)
where <mode> is either convenience or conservation. By default, the class defaults mode is
convenience. If the mode is convenience, then for the purposes of role inheritance, system
defined class behave as concrete classes; for the purpose of pattern-match inheritance, system
defined classes behave as reactive classes unless the inheriting class is abstract; and the default
setting for the create-accessor facet of the class’ slots is read-write. If the class defaults mode is
conservation, then the role and reactivity of system-defined classes is unchanged for the purposes
of role and pattern-match inheritance and the default setting for the create-accessor facet of the
class’ slots is ?NONE.
12.16.1.26 Getting the Defaults Mode for Classes
This function returns the current defaults mode used when classes are defined (convenience or
conservation).
Syntax
(get-class-defaults-mode)
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12.16.1.27 Getting the Allowed Values for a Slot
This function groups the allowed classes for a slot (specified by the allowed-classes facet for the
slot) into a multifield variable. If the allowed-classes facet was not specified for the slot, then the
symbol FALSE is returned. A multifield of length zero is returned if an error occurs.
Syntax
(slot-allowed-classes <class-name> <slot-name>)
Example
CLIPS> (clear)
CLIPS> (defclass A (is-a USER))
CLIPS> (defclass B (is-a USER) (slot x))
CLIPS> (defclass C (is-a USER) (slot y (allowed-classes A B)))
CLIPS> (slot-allowed-classes B x)
FALSE
CLIPS> (slot-allowed-classes C y)
(A B)
CLIPS>
12.16.2 Message-handler Functions
12.16.2.1 Existence of Shadowed Handlers
This function returns the symbol TRUE if there is another message-handler available for
execution, FALSE otherwise. If this function is called from an around handler and there are any
shadowed handlers (see section 9.5.3), the return value is the symbol TRUE. If this function is
called from a primary handler and there are any shadowed primary handlers, the return value is
the symbol TRUE. In any other circumstance, the return value is the symbol FALSE.
Syntax
(next-handlerp)
12.16.2.2 Calling Shadowed Handlers
If the conditions are such that the function next-handlerp would return the symbol TRUE, then
calling this function will execute the shadowed method. Otherwise, a message execution error
(see section 9.5.4) will occur. In the event of an error, the return value of this function is the
symbol FALSE, otherwise it is the return value of the shadowed handler. The shadowed handler
is passed the same arguments as the calling handler.
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A handler may continue execution after calling call-next-handler. In addition, a handler may
make multiple calls to call-next-handler, and the same shadowed handler will be executed each
time.
Syntax
(call-next-handler)
Example
CLIPS> (clear)
CLIPS> (defclass A (is-a USER))
CLIPS>
(defmessage-handler A print-args ($?any)
(printout t "A: " ?any crlf)
(if (next-handlerp) then
(call-next-handler)))
CLIPS>
(defmessage-handler USER print-args ($?any)
(printout t "USER: " ?any crlf))
CLIPS> (make-instance a of A)
[a]
CLIPS> (send [a] print-args 1 2 3 4)
A: (1 2 3 4)
USER: (1 2 3 4)
CLIPS>
12.16.2.3 Calling Shadowed Handlers with Different Arguments
This function is identical to call-next-handler except that this function can change the
arguments passed to the shadowed handler.
Syntax
(override-next-handler <expression>*)
Example
CLIPS> (clear)
CLIPS> (defclass A (is-a USER))
CLIPS>
(defmessage-handler A print-args ($?any)
(printout t "A: " ?any crlf)
(if (next-handlerp) then
(override-next-handler (rest$ ?any))))
CLIPS>
(defmessage-handler USER print-args ($?any)
(printout t "USER: " ?any crlf))
CLIPS> (make-instance a of A)
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[a]
CLIPS> (send [a] print-args 1 2 3 4)
A: (1 2 3 4)
USER: (2 3 4)
CLIPS>
12.16.3 Definstances Functions
12.16.3.1 Getting the List of Definstances
The function get-definstances-list returns a multifield value containing the names of all
definstances constructs visible to the module specified by <module-name> or to the current
module if none is specified. If * is specified as the module name, then all definstances are
returned.
Syntax
(get-definstances-list [<module-name>])
Example
CLIPS> (clear)
CLIPS> (get-definstances-list)
(initial-object)
CLIPS> (definstances foo)
CLIPS> (definstances bar)
CLIPS> (get-definstances-list)
(initial-object foo bar)
CLIPS>>
12.16.3.2 Determining the Module in which a Definstances is Defined
This function returns the module in which the specified definstances name is defined.
Syntax
(definstances-module <definstances-name>)
12.16.4 Instance Manipulation Functions and Actions
12.16.4.1 Initializing an Instance
This function implements the init message-handler attached to the class USER (see section
9.4.5.1). This function evaluates and places slot expressions given by the class definition that
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were not specified by slot-overrides in the call to make-instance or initialize-instance (see
section 9.6.1). This function should never be called directly unless an init message-handler is
being defined such that the one attached to USER will never be called. However, such a
definition is unusual and recommended only to advanced users. A user-defined class which does
not inherit indirectly or directly from the class USER will require an init message-handler which
calls this function in order for instances of the class to be created. If this function is called from
an init message within the context of a make-instance or initialize-instance call and there are
no errors in evaluating the class defaults, this function will return the address of the instance it is
initializing. Otherwise, this function will return the symbol FALSE.
Syntax
(init-slots)
12.16.4.2 Deleting an Instance
This function deletes the specified instances by sending them a delete message. The argument
can be one or more instance-names, instance-addresses, or symbols (an instance-name without
enclosing brackets). The instance specified by the arguments must exist (except in the case of
“*”). If “*” is specified for the instance, all instances will be sent the delete message (unless
there is an instance named “*”). This function returns the symbol TRUE if all instances were
successfully deleted, otherwise it returns the symbol FALSE. Note, this function is exactly
equivalent to sending the instance(s) the delete message directly and is provided only as an
intuitive counterpart to the function retract for facts.
Syntax
(unmake-instance <instance-expression>+)
12.16.4.3 Deleting the Active Instance from a Handler
This function operates implicitly on the active instance (see section 9.4.1.1) for a message, and
thus can only be called from within the body of a message-handler. This function directly deletes
the active instance and is the one used to implement the delete handler attached to class USER
(see section 9.4.5.2). This function returns the symbol TRUE if the instance was successfully
deleted, otherwise the symbol FALSE.
Syntax
(delete-instance)
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12.16.4.4 Determining the Class of an Object
This function returns a symbol which is the name of the class of its argument. It returns the
symbol FALSE on errors. This function is equivalent to the type function (see section 12.15.4).
Syntax
(class <object-expression>)
Example
CLIPS> (class 34)
INTEGER
CLIPS>
12.16.4.5 Determining the Name of an Instance
This function returns a symbol which is the name of its instance argument. It returns the symbol
FALSE on errors. The evaluation of the argument must be an instance-name or instance-address
of an existing instance.
Syntax
(instance-name <instance-expression>)
12.16.4.6 Determining the Address of an Instance
This function returns the address of its instance argument. It returns the symbol FALSE on
errors. The evaluation of <instance expression> must be an instance-name or instance-address of
an existing instance. If <module> or * is not specified, the function searches only in the current
module. If * is specified, the current module and imported modules are recursively searched. If
<module> is specified, only that module is searched. The :: syntax cannot be used with the
instance-name if <module> or * is specified.
Syntax
(instance-address [<module> | *] <instance-expression>)
12.16.4.7 Converting a Symbol to an Instance-Name
This function returns an instance-name which is equivalent to its symbol argument. It returns the
symbol FALSE on errors.
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Syntax
(symbol-to-instance-name <symbol-expression>)
Example
CLIPS> (symbol-to-instance-name (sym-cat abc def))
[abcdef]
CLIPS>
12.16.4.8 Converting an Instance-Name to a Symbol
This function returns a symbol which is equivalent to its instance-name argument. It returns the
symbol FALSE on errors.
Syntax
(instance-name-to-symbol <instance-name-expression>)
Example
CLIPS> (instance-name-to-symbol [a])
a
CLIPS>
12.16.4.9 Predicate Functions
12.16.4.9.1 Testing for an Instance
This function returns the symbol TRUE if the evaluation of its argument is an instance-address
or an instance-name. Otherwise, it returns the symbol FALSE.
Syntax
(instancep <expression>)
12.16.4.9.2 Testing for an Instance-Address
This function returns the symbol TRUE if the evaluation of its argument is an instance-address.
Otherwise, it returns the symbol FALSE.
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Syntax
(instance-addressp <expression>)
12.16.4.9.3 Testing for an Instance-Name
This function returns the symbol TRUE if the evaluation of its argument is an instance-name.
Otherwise, it returns the symbol FALSE.
Syntax
(instance-namep <expression>)
12.16.4.9.4 Testing for the Existence an Instance
This function returns the symbol TRUE if the specified instance exists. Otherwise, it returns the
symbol FALSE. If the argument is an instance-name, the function determines if an instance of
the specified name exists. If the argument is an instance-address, the function determines if the
specified address is still valid.
Syntax
(instance-existp <instance-expression>)
12.16.4.10 Reading a Slot Value
This function returns the value of the specified slot of the active instance (see section 9.4.1.1). If
the slot does not exist, the slot does not have a value or this function is called from outside a
message-handler, this function will return the symbol FALSE and an error will be generated.
This function differs from the ?self:<slot-name> syntax in that the slot is not looked up until the
function is actually called. Thus it is possible to access different slots every time the function is
executed (see section 9.4.2 for more detail). This function bypasses message-passing.
Syntax
(dynamic-get <slot-name-expression>)
12.16.4.11 Setting a Slot Value
This function sets the value of the specified slot of the active instance (see section 9.4.1.1). If the
slot does not exist, there is an error in evaluating the arguments to be placed or this function is
called from outside a message-handler, this function will return the symbol FALSE and an error
will be generated. Otherwise, the new slot value is returned. This function differs from the (bind
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?self:<slot-name> <value>*) syntax in that the slot is not looked up until the function is actually
called. Thus it is possible to access different slots every time the function is executed (see section
9.4.2 for more detail). This function bypasses message-passing.
Syntax
(dynamic-put <slot-name-expression> <expression>*)
12.16.4.12 Multifield Slot Functions
The following functions allow convenient manipulation of multifield slots. There are three types
of functions: replacing a range of fields with one or more new values, inserting one or more new
values at an arbitrary point, and deleting a range of fields. For each type, there are two forms of
functions: an external interface which sets the new value for the multifield slot with a
put- message (see section 9.3.3.9), and an internal interface that can only be called from
message-handlers which sets the slot for the active instance (see section 9.4.1.1) directly. Both
forms read the original value of the slot directly without the use of a get- message. All of these
functions return the new slot value on success and the symbol FALSE on errors.
12.16.4.12.1 Replacing Fields
Allows the replacement of a range of fields in a multifield slot value with one or more new
values. The range indices must be from 1..n, where n is the number of fields in the multifield
slot’s original value and n > 0.
External Interface Syntax
(slot-replace$ <instance-expression> <mv-slot-name>
<range-begin> <range-end> <expression>+)
Internal Interface Syntax
(slot-direct-replace$ <mv-slot-name>
<range-begin> <range-end> <expression>+)
Example
CLIPS>
(defclass A (is-a USER)
(multislot mfs (default a b c d e)))
CLIPS> (make-instance a of A)
[a]
CLIPS> (slot-replace$ a mfs 2 4 2 3 4)
(a 2 3 4 e)
CLIPS>
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12.16.4.12.2 Inserting Fields
Allows the insertion of one or more new values in a multifield slot value before a specified field
index. The index must greater than or equal to 1. A value of 1 inserts the new value(s) at the
beginning of the slot’s value. Any value greater than the length of the slot’s value appends the
new values to the end of the slot’s value.
External Interface Syntax
(slot-insert$ <instance-expression> <mv-slot-name>
<index> <expression>+)
Internal Interface Syntax
(slot-direct-insert$ <mv-slot-name> <index> <expression>+)
Example
CLIPS> (initialize-instance a)
[a]
CLIPS> (slot-insert$ a mfs 2 4 2 3 4)
(a 4 2 3 4 b c d e)
CLIPS>
12.16.4.12.3 Deleting Fields
Allows the deletion of a range of fields in a multifield slot value. The range indices must be from
1..n, where n is the number of fields in the multifield slot’s original value and n > 0.
External Interface Syntax
(slot-delete$ <instance-expression> <mv-slot-name>
<range-begin> <range-end>)
Internal Interface Syntax
(slot-direct-delete$ <mv-slot-name> <range-begin> <range-end>)
Example
CLIPS> (initialize-instance a)
[a]
CLIPS> (slot-delete$ a mfs 2 4)
(a e)
CLIPS>
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12.17 Defmodule Functions
The following functions provide ancillary capabilities for the defmodule construct.
12.17.1 Getting the List of Defmodules
The function get-defmodule-list returns a multifield value containing the names of all
defmodules that are currently defined.
Syntax
(get-defmodule-list)
Example
CLIPS> (clear)
CLIPS> (get-defmodule-list)
(MAIN)
CLIPS> (defmodule A)
CLIPS> (defmodule B)
CLIPS> (get-defmodule-list)
(MAIN A B)
CLIPS>
12.17.2 Setting the Current Module
This function sets the current module. It returns the name of the previous current module. If an
invalid module name is given, then the current module is not changed and the name of the
current module is returned.
Syntax
(set-current-module <defmodule-name>)
12.17.3 Getting the Current Module
This function returns the name of the current module.
Syntax
(get-current-module)
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12.18 Sequence Expansion
By default, there is no distinction between single-field and multifield variable references within
function calls (as opposed to declaring variables for function parameters or variables used for
pattern-matching). For example:
CLIPS> (clear)
CLIPS>
(defrule expansion
(foo $?b)
=>
(printout t ?b crlf)
(printout t $?b crlf))
CLIPS> (assert (foo a b c))
<Fact-1>
CLIPS> (run)
(a b c)
(a b c)
CLIPS>
Note that both printout statements in the rule produce identical output when the rule executes.
The use of ?b and $?b within the function call behave identically.
Multifield variable references within function calls, however, can optionally be expanded into
multiple single field arguments. The $ acts as a “sequence expansion” operator and has special
meaning when applied to a global or local variable reference within the argument list of a
function call. The $ means to take the fields of the multifield value referenced by the variable
and treat them as separate arguments to the function as opposed to passing a single multifield
value argument.
For example, using sequence expansion with the expansion rule would give the following output:
CLIPS> (clear)
CLIPS> (set-sequence-operator-recognition TRUE)
TRUE
CLIPS>
(defrule expansion
(foo $?b)
=>
(printout t ?b crlf)
(printout t $?b crlf))
CLIPS> (assert (foo a b c))
<Fact-1>
CLIPS> (run)
(a b c)
abc
CLIPS> (set-sequence-operator-recognition FALSE)
TRUE
CLIPS>
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Using sequence expansion, the two printout statements on the RHS of the expansion rule are
equivalent to:
(printout t (create$ a b c) crlf)
(printout t a b c crlf)
The $ operator also works with global variables. For example:
CLIPS> (clear)
CLIPS> (set-sequence-operator-recognition TRUE)
FALSE
CLIPS> (defglobal ?*x* = (create$ 3 4 5))
CLIPS> (+ ?*x*)
[ARGACCES4] Function + expected at least 2 argument(s)
CLIPS> (+ $?*x*)
12
CLIPS> (set-sequence-operator-recognition FALSE)
TRUE
CLIPS>
The sequence expansion operator is particularly useful for generic function methods. Consider
the ease now of defining a general addition function for strings.
(defmethod + (($?any STRING))
(str-cat $?any))
By default, sequence expansion is disabled. This allows previously existing CLIPS programs to
work correctly with version 6.0 of CLIPS. The behavior can be enabled using the
set-sequence-operator-recognition function described in section 12.18.3. Old CLIPS code
should be changed so that it works properly with sequence expansion enabled.
12.18.1 Sequence Expansion and Rules
Sequence expansion is allowed on the LHS of rules, but only within function calls. If a variable
is specified in a pattern as a single or multifield variable, then all other references to that variable
that are not within function calls must also be the same. For example, the following rule is not
allowed
(defrule bad-rule-1
(pattern $?x ?x $?x)
=>)
The following rules illustrate appropriate use of sequence expansion on the LHS of rules.
(defrule good-rule-1
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(pattern $?x&:(> (length$ ?x) 1))
(another-pattern $?y&:(> (length$ ?y) 1))
(test (> (+ $?x) (+ $?y)))
=>)
The first and second patterns use the length$ function to determine that the multifields bound to
?x and ?y are greater than 1. Sequence expansion is not used to pass ?x and ?y to the length$
function since the length$ function expects a single argument of type multifield. The test CE
calls the + function to determine the sum of the values bound to ?x and ?y. Sequence expansion
is used for these function calls since the + function expects two or more arguments with numeric
data values.
Sequence expansion has no affect within an assert, modify, or duplicate; however, it can be
used with other functions on the RHS of a rule.
12.18.2 Multifield Expansion Function
The $ operator is merely a shorthand notation for the expand$ function call. For example, the
function calls
(printout t $?b crlf)
and
(printout t (expand$ ?b) crlf)
are identical.
Syntax
(expand$ <multifield-expression>)
The expand$ function is valid only within the argument list of a function call. The expand$
function (and hence sequence expansion) cannot be used as an argument to the following
functions: expand$, return, progn, while, if, progn$, foreach, switch, loop-for-count, assert,
modify, duplicate and object-pattern-match-delay.
12.18.3 Setting The Sequence Operator Recognition Behavior
This function sets the sequence operator recognition behavior. When this behavior is disabled
(FALSE by default), multifield variables found in function calls are treated as a single argument.
When this behaviour is enabled, multifield variables are expanded and passed as separate
arguments in the function call. This behavior should be set before an expression references a
multifield variable is encountered (i.e. changing the behavior does not retroactively change the
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behavior for previously encountered expressions). The return value for this function is the old
value for the behavior.
Syntax
(set-sequence-operator-recognition <boolean-expression>)
12.18.4 Getting The Sequence Operator Recognition Behavior
This function returns the current value of the sequence operator recognition behavior (TRUE or
FALSE).
Syntax
(get-sequence-operator-recognition)
12.18.5 Sequence Operator Caveat
CLIPS normally tries to detect as many constraint errors as possible for a function call at parse
time, such as bad number of arguments or types. However, if the sequence expansion operator is
used in the function call, all such checking is delayed until run-time (because the number and
types of arguments can change for each execution of the call.) For example:
CLIPS> (clear)
CLIPS> (set-sequence-operator-recognition TRUE)
FALSE
CLIPS> (deffunction foo (?a ?b))
CLIPS> (deffunction bar ($?a) (foo ?a))
[ARGACCES4] Function foo expected exactly 2 argument(s)
ERROR:
(deffunction MAIN::bar
($?a)
(foo ?a)
CLIPS> (deffunction bar ($?a) (foo $?a))
CLIPS> (bar 1)
[ARGACCES4] Function foo expected exactly 2 argument(s)
[PRCCODE4] Execution halted during the actions of deffunction bar.
FALSE
CLIPS> (bar 1 2)
FALSE
CLIPS> (set-sequence-operator-recognition FALSE)
TRUE
CLIPS>
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Section 13:
Commands
This section describes commands primarily intended for use from the top-level command
prompt. These commands may also be used from constructs and other places where functions
can be used.
13.1 Environment Commands
The following commands control the CLIPS environment.
13.1.1 Loading Constructs From A File
Loads the constructs stored in the file specified by <file-name> into the environment. If the
compilations item is being watched (see section 13.2), then an informational message (including
the type and name of the construct) will be displayed for each construct loaded. If the
compilations item is not being watched, then a character is printed for each construct loaded (“*”
for defrule, “$” for deffacts, “%” for deftemplate, “:” for defglobal, “!” for deffunction, “^” for
defgeneric, “&” for defmethod, “#” for defclass, “~” for defmessage-handler, “@” for
definstances, and “+” for defmodule). This function returns TRUE if the file was successfully
loaded, otherwise FALSE is returned.
Syntax
(load <file-name>)
13.1.2 Loading Constructs From A File without Progress Information
Loads the constructs stored in the file specified by <file-name> into the environment, however,
unlike the load command informational messsages are not printed to show the progress of
loading the file. Error messages are still printed if errors are encountered while loading the file.
This function returns TRUE if the file was successfully loaded, otherwise FALSE is returned.
Syntax
(load* <file-name>)
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13.1.3 Saving All Constructs To A File
Saves all of the constructs (defrules, deffacts, deftemplates, etc.) in the current environment into
the file specified by <file-name>. Note that deffunctions and generic functions are saved twice to
the file. Because it is possible to create circular references among deffunctions and generic
functions by redefining them, a forward declaration (containing no actions) of each function is
saved first to the file, and then the actual declaration (containing the actions) is saved. This
function returns TRUE if the file was successfully saved, otherwise FALSE is returned. This
function uses the pretty-print forms of the constructs. If pretty-printing has been disabled by the
conserve-mem command, then the save command will have no output.
Syntax
(save <file-name>)
13.1.4 Loading a Binary Image
Loads the constructs stored in the binary file specified by <file-name> into the environment. The
specified file must have been created by bsave. Loading a binary image is quicker than using the
load command to load a ASCII text file. A bload clears all constructs from the current CLIPS
environment (as well as all facts and instances). Bload can be called at any time unless some
constructs that bload will affect are in use (e.g. a deffunction is currently executing). The only
constructive/destructive operation that can occur after a bload is the clear command or the bload
command (which clears the current binary image). This means that constructs cannot be loaded
or deleted while a bload is in effect. In order to add constructs to a binary image, the original
ASCII text file must be reloaded, the new constructs added, and then another bsave must be
performed. This function returns TRUE if the file was successfully bloaded, otherwise FALSE is
returned.
Binary images can be loaded into different compile-time configurations of CLIPS, as long as the
same version of CLIPS is used and all the functions and constructs needed by the binary image
are supported. In addition, binary images should theoretically work across different hardware
platforms if internal data representations are equivalent (e.g. same integer size, same byte order,
same floating-point format, etc). However, it is NOT recommended that this be attempted.
Syntax
(bload <file-name>)
13.1.5 Saving a Binary Image
Saves all of the constructs in the current environment into the file specified by <file-name>. The
save file is written using a binary format which results in faster load time. The save file must be
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loaded via the bload command. A bsave may be performed at any time (except when a bload is
in effect). The pretty print representation of a construct is not saved with a binary image (thus,
commands like ppdefrule will show no output for any of the rules associated with the binary
image). In addition, constraint information associated with constructs is not saved to the binary
image unless dynamic constraint checking is enabled (using the
set-dynamic-constraint-checking command). This function returns TRUE if the file was
successfully bsaved, otherwise FALSE is returned.
Syntax
(bsave <file-name>)
13.1.6 Clearing CLIPS
Clears CLIPS. Removes all constructs and all associated data structures (such as facts and
instances) from the CLIPS environment. A clear may be performed safely at any time, however,
certain constructs will not allow themselves to be deleted while they are in use. For example,
while deffacts are being reset (by the reset command), it is not possible to remove them using
the clear command. Note that the clear command does not effect many environment
characteristics (such as the current conflict resolution strategy). This function has no return
value.
Syntax
(clear)
13.1.7 Exiting CLIPS
Quits CLIPS. This function has no return value.
Syntax
(exit [<integer-expression>])
The optional <integer-expression> argument allows the exit status code to be specified which is
eventually passed to the C exit function.
13.1.8 Resetting CLIPS
Resets CLIPS. Removes all activations from the agenda, all facts from the fact-list and all
instances of user-defined classes, then assigns global variables their initial values, asserts all
facts listed in deffacts statements into the fact-list, creates all instances listed in definstances
statements, sets the current module to the MAIN module and automatically focuses on the same
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module. Incremental reset is supported for rules. This means that rules can be activated from
facts that were asserted before the rule was defined without performing a reset. A reset can be
performed while rules are executing. Note that the reset command does not effect many
environment characteristics (such as the current conflict resolution strategy). This function has
no return value.
Syntax
(reset)
13.1.9 Executing Commands From a File
Allows “batch” processing of CLIPS interactive commands by replacing standard input with the
contents of a file. Any command or function can be used in a batch file, as well as construct
definitions and responses to read or readline function calls. The load command should be used
in batch files rather than defining constructs directly. The load command expects only constructs
and hence moves to the next construct when an error occurs. The batch command, however,
moves on until it finds the next construct or command (and in the case of a construct this is
likely to generate more errors as the remaining commands and functions in the construct are
parsed). This function returns TRUE if the batch file was successfully executed, otherwise
FALSE is returned. Note that the batch command operates by replacing standard input rather
than by immediately executing the commands found in the batch file. In effect, if you execute a
batch command from the RHS of a rule, the commands in that batch file will not be processed
until control is returned to the top-level prompt.
Syntax
(batch <file-name>)
13.1.10 Executing Commands From a File Without Replacing Standard Input
Evaluates the series of commands stored in the file specified by <file-name>. Unlike the batch
command, batch* evaluates all of the commands in the specified file before returning. The
batch* command does not replace standard input and thus a batch* file cannot be used to
provide input to functions such as read and readline. In addition, commands stored in the
batch* file and the return value of these commands are not echoed to standard output.
The batch* command is not available for binary-load only or run-time CLIPS configurations
(see the Advanced Programming Guide).
Syntax
(batch* <file-name>)
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13.1.11 Determining CLIPS Compilation Options
Generates a textual description of the settings of the CLIPS compiler flags. This function has no
return value.
Syntax
(options)
13.1.12 Calling the Operating System
The system function allows a call to the operating system. It is patterned after the system
function provided to C on most UNIX systems. This function has no return value.
Syntax
(system <lexeme-expression>*)
Example
(defrule print-directory
(print-directory ?directory)
=>
(system "dir " ?directory)); Note space => "dir<space>"
Note that any spaces needed for a proper parsing of the system command must be added by the
user in the call to system. Also note that the system command is not guaranteed to execute (e.g.,
the operating system may not have enough memory to spawn a new process).
! Portability Note
Not all operating systems/compilers provide this function. The code is stored in the sysdep.c file,
and the default coding for generic CLIPS is a nonfunctional stub that will compile on any
machine. On some machines (such as an IBM PC running DOS), there may be insufficient
memory available to spawn a subprocess to execute the system command. In such a case, the
command will not be executed and the system command will return with no action taken.
13.1.13 Setting The Auto-Float Dividend Behavior
This function sets auto-float dividend behavior. When this behavior is enabled (TRUE by
default) the dividend of the division function is automatically converted to a floating point
number. The return value for this function is the old value for the behavior.
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Syntax
(set-auto-float-dividend <boolean-expression>)
13.1.14 Getting The Auto-Float Dividend Behavior
This function returns the current value of the auto-float dividend behavior (TRUE or FALSE).
Syntax
(get-auto-float-dividend)
13.1.15 Setting the Dynamic Constraint Checking Behavior
This function sets dynamic constraint checking behavior. When this behavior is disabled
(FALSE by default), newly created data objects (such as deftemplate facts and instances) do not
have their slot values checked for constraint violations. When this behavior is enabled (TRUE),
the slot values are checked for constraint violations. The return value for this function is the old
value for the behavior. Constraint information is not saved when using the bload and
constructs-to-c command if dynamic constraint checking is disabled.
Syntax
(set-dynamic-constraint-checking <boolean-expression>)
13.1.16 Getting the Dynamic Constraint Checking Behavior
This function returns the current value of the dynamic constraint checking behavior (TRUE or
FALSE).
Syntax
(get-dynamic-constraint-checking)
13.1.17 Setting the Static Constraint Checking Behavior
This function sets static constraint checking behavior. When this behavior is disabled (FALSE),
constraint violations are not checked when function calls and constructs are parsed. When this
behavior is enabled (TRUE by default), constraint violations are checked when function calls and
constructs are parsed. The return value for this function is the old value for the behavior.
Syntax
(set-static-constraint-checking <boolean-expression>)
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13.1.18 Getting the Static Constraint Checking Behavior
This function returns the current value of the static constraint checking behavior (TRUE or
FALSE).
Syntax
(get-static-constraint-checking)
13.1.19 Finding Symbols
This command displays all symbols currently defined in CLIPS which contain a specified
substring. This command has no return value.
Syntax
(apropos <lexeme>)
Example
CLIPS> (apropos pen)
dependents
mv-append
open
dependencies
CLIPS>
13.2 Debugging Commands
The following commands control the CLIPS debugging features.
13.2.1 Generating Trace Files
Sends all information normally sent to the logical names wclips, wdialog, wdisplay, werror,
wwarning, wtrace, and stdout to <file-name> as well as to their normal destination.
Additionally, all information received from logical name stdin is also sent to <file-name> as
well as being returned by the requesting function. This function returns TRUE if the dribble file
was successfully opened, otherwise FALSE is returned.
Syntax
(dribble-on <file-name>)
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13.2.2 Closing Trace Files
Stops sending trace information to the dribble file. This function returns TRUE if the dribble file
was successfully closed, otherwise FALSE is returned.
Syntax
(dribble-off)
13.2.3 Enabling Watch Items
This function causes messages to be displayed when certain CLIPS operations take place.
Syntax
(watch <watch-item>)
<watch-item> ::= all |
compilations |
statistics |
focus |
messages |
deffunctions <deffunction-name>* |
globals <global-name>* |
rules <rule-name>* |
activations <rule-name>* |
facts <deftemplate-name>* |
instances <class-name>* |
slots <class-name>* |
message-handlers <handler-spec-1>*
[<handler-spec-2>]) |
generic-functions <generic-name>* |
methods <method-spec-1>* [<method-spec-2>]
<handler-spec-1> ::= <class-name>
<handler-name> <handler-type>
<handler-spec-2> ::= <class-name>
[<handler-name> [<handler-type>]]
<method-spec-1> ::= <generic-name> <method-index>
<method-spec-2> ::= <generic-name> [<method-index>]
If compilations are watched, the progress of construct definitions will be displayed.
If facts are watched, all fact assertions and retractions will be displayed. Optionally, facts
associated with individual deftemplates can be watched by specifying one or more deftemplate
names.
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If rules are watched, all rule firings will be displayed. If activations are watched, all rule
activations and deactivations will be displayed. Optionally, rule firings and activations associated
with individual defrules can be watched by specifying one or more defrule names. If statistics
are watched, timing information along with other information (average number of facts, average
number of activations, etc.) will be displayed after a run. Note that the number of rules fired and
timing information is not printed unless this item is being watch. If focus is watched, then
changes to the current focus will be displayed.
If globals are watched, variable assignments to globals variables will be displayed. Optionally,
variable assignments associated with individual defglobals can be watched by specifying one or
more defglobal names. If deffunctions are watched, the start and finish of deffunctions will be
displayed. Optionally, the start and end display associated with individual deffunctions can be
watched by specifying one or more deffunction names.
If generic-functions are watched, the start and finish of generic functions will be displayed.
Optionally, the start and end display associated with individual defgenerics can be watched by
specifying one or more defgeneric names. If methods are watched, the start and finish of
individual methods within a generic function will be displayed. Optionally, individual methods
can be watched by specifying one or more methods using a defgeneric name and a method index.
When the method index is not specified, then all methods of the specified defgeneric will be
watched.
If instances are watched, creation and deletion of instances will be displayed. If slots are
watched, changes to any instance slot values will be displayed. Optionally, instances and slots
associated with individual concrete defclasses can be watched by specifying one or more
concrete defclass names. If message-handlers are watched, the start and finish of individual
message-handlers within a message will be displayed. Optionally, individual message-handlers
can be watched by specifying one or more message-handlers using a defclass name, a
message-handler name, and a message-handler type. When the message-handler name and
message-handler type are not specified, then all message-handlers for the specified class will be
watched. When the message-handler type is not specified, then all message-handlers for the
specified class with the specified message-handler name will be watched. If messages are
watched, the start and finish of messages will be displayed.
For the watch items that allow individual constructs to be watched, if no constructs are specified,
then all constructs of that type will be watched. If all constructs associated with a watch item are
being watched, then newly defined constructs of the same type will also be watched. A construct
retains its old watch state if it is redefined. If all is watched, then all other watch items will be
watched. By default, only compilations are watched. The watch function has no return value.
Example
CLIPS> (watch rules)
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CLIPS>
13.2.4 Disabling Watch Items
This function disables the effect of the watch command.
Syntax
(unwatch <watch-item>)
This command is identical to the watch command with the exception that it disables watch items
rather than enabling them. This function has no return value.
Example
CLIPS> (unwatch all)
CLIPS>
13.2.5 Viewing the Current State of Watch Items
This command displays the current state of watch items.
Syntax
(list-watch-items [<watch-item>])
This command displays the current state of all watch items. If called without the <watch-item>
argument, the global watch state of all watch items is displayed. If called with the <watch-item>
argument, the global watch state for that item is displayed followed by the individual watch
states for each item of the specified type which can be watched. This function has no return
value.
Example
CLIPS> (list-watch-items)
facts = off
instances = off
slots = off
rules = off
activations = off
messages = off
message-handlers = off
generic-functions = off
methods = off
deffunctions = off
compilations = on
statistics = off
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globals = off
focus = off
CLIPS> (list-watch-items facts)
facts = off
MAIN:
initial-fact = off
CLIPS>
13.3 Deftemplate Commands
The following commands manipulate deftemplates.
13.3.1 Displaying the Text of a Deftemplate
Displays the text of a given deftemplate. This function has no return value.
Syntax
(ppdeftemplate <deftemplate-name>)
13.3.2 Displaying the List of Deftemplates
Displays the names of all deftemplates. This function has no return value.
Syntax
(list-deftemplates [<module-name>])
If <module-name> is unspecified, then the names of all deftemplates in the current module are
displayed. If <module-name> is specified, then the names of all deftemplates in the specified
module are displayed. If <module-name> is the symbol *, then the names of all deftemplates in
all modules are displayed.
13.3.3 Deleting a Deftemplate
This function deletes a previously defined deftemplate.
Syntax
(undeftemplate <deftemplate-name>)
If the deftemplate is in use (for example by a fact or a rule), then the deletion will fail.
Otherwise, no further uses of the deleted deftemplate are permitted (unless redefined). If the
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symbol * is used for <deftemplate-name>, then all deftemplates will be deleted (unless there is a
deftemplate named *). This function has no return value.
13.4 Fact Commands
The following commands display information about facts.
13.4.1 Displaying the Fact-List
Displays facts stored in the fact-list.
Syntax
(facts [<module-name>]
[<start-integer-expression>
[<end-integer-expression>
[<max-integer-expression>]]])
If <module-name> is not specified, then only facts visible to the current module will be
displayed. If <module-name> is specified, then only facts visible to the specified module are
displayed. If the symbol * is used for <module-name>, then facts from any module may be
displayed. If the start argument is specified, only facts with fact-indices greater than or equal to
this argument are displayed. If the end argument is specified, only facts with fact-indices less
than or equal to this argument are displayed. If the max argument is specified, then no facts will
be displayed beyond the specified maximum number of facts to be displayed. This function has
no return value.
13.4.2 Loading Facts From a File
This function will assert a file of information as facts into the CLIPS fact-list. It can read files
created with save-facts or any ASCII text file. Each fact should begin with a left parenthesis and
end with a right parenthesis. Facts may span across lines and can be written in either ordered or
deftemplate format. This function returns TRUE if the fact file was successfully loaded,
otherwise FALSE is returned.
Syntax
(load-facts <file-name>)
13.4.3 Saving The Fact-List To A File
This function saves all of the facts in the current fact-list into the file specified by <file-name>.
External-address and fact-address fields are saved as strings. Instance-address fields are
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converted to instance-names. Optionally, the scope of facts to be saved can be specified. If
<save-scope> is the symbol visible, then all facts visible to the current module are saved. If
<save-scope> is the symbol local, then only those facts with deftemplates defined in the current
module are saved. If <save-scope> is not specified, it defaults to local. If <save-scope> is
specified, then one or more deftemplate names may also be specified. In this event, only those
facts with associated with a corresponding deftemplate in the specified list will be saved. This
function returns TRUE if the fact file was successfully saved, otherwise FALSE is returned.
Syntax
(save-facts <file-name> [<save-scope> <deftemplate-names>*])
<save-scope> ::= visible | local
13.4.4 Setting the Duplication Behavior of Facts
This function sets fact duplication behavior. When this behavior is disabled (FALSE by default),
asserting a duplicate of a fact already in the fact-list produces no effect. When enabled (TRUE),
the duplicate fact is asserted with a new fact-index. The return value for this function is the old
value for the behavior.
Syntax
(set-fact-duplication <boolean-expression>)
Example
CLIPS> (clear)
CLIPS> (get-fact-duplication)
FALSE
CLIPS> (watch facts)
CLIPS> (assert (a))
==> f-1 (a)
<Fact-1>
CLIPS> (assert (a))
FALSE
CLIPS> (set-fact-duplication TRUE)
FALSE
CLIPS> (assert (a))
==> f-2 (a)
<Fact-2>
CLIPS> (unwatch facts)
CLIPS> (set-fact-duplication FALSE)
TRUE
CLIPS>
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13.4.5 Getting the Duplication Behavior of Facts
This function returns the current value of the fact duplication behavior (TRUE or FALSE).
Syntax
(get-fact-duplication)
13.4.6 Displaying a Single Fact
Displays a single fact, placing each slot and its value on a separate line. Optionally the logical
name to which output is sent can be specified and slots containing their default values can be
excluded from the output. If <logical-name> is t or unspecified, then output is sent to the logical
name stdout, otherwise it is sent to the specified logical name. If <ignore-defaults-flag> is
FALSE or unspecified, then all of the fact’s slots are displayed, otherwise slots with static
defaults are only displayed if their current slot value differs from their initial default value.
Syntax
(ppfact <fact-specifier> [<logical-name> [<ignore-defaults-flag>]])
Example
CLIPS> (clear)
CLIPS>
(deftemplate foo
(slot x (default 3))
(slot y)
(multislot z (default a b)))
CLIPS> (assert (foo))
<Fact-1>
CLIPS> (ppfact 1 t)
(foo
(x 3)
(y nil)
(z a b))
CLIPS> (ppfact 1 t TRUE)
(foo)
CLIPS> (modify 1 (y 2) (z c))
<Fact-2>
CLIPS> (ppfact 2 t TRUE)
(foo
(y 2)
(z c))
CLIPS>
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13.5 Deffacts Commands
The following commands manipulate deffacts.
13.5.1 Displaying the Text of a Deffacts
Displays the text of a given deffacts. This function has no return value.
Syntax
(ppdeffacts <deffacts-name>)
13.5.2 Displaying the List of Deffacts
Displays the names of all deffacts stored in the CLIPS environment.
Syntax
(list-deffacts [<module-name>])
If <module-name> is unspecified, then the names of all deffacts in the current module are
displayed. If <module-name> is specified, then the names of all deffacts in the specified module
are displayed. If <module-name> is the symbol *, then the names of all deffacts in all modules
are displayed. This function has no return value.
13.5.3 Deleting a Deffacts
This function deletes a previously defined deffacts.
Syntax
(undeffacts <deffacts-name>)
All facts listed in the deleted deffacts construct will no longer be asserted as part of a reset. If the
symbol * is used for <deffacts-name>, then all deffacts will be deleted (unless there exists a
deffacts named *). The undeffacts command can be used to remove deffacts at any time.
Exceptions: When deffacts are being reset as part of the reset command, they cannot be
removed. This function has no return value.
13.6 Defrule Commands
The following commands manipulate defrules.
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13.6.1 Displaying the Text of a Rule
Displays the text of a given rule.
Syntax
(ppdefrule <rule-name>)
The pprule command can also be used for this purpose. This function has no return value.
13.6.2 Displaying the List of Rules
Displays the names of all rules stored in the CLIPS environment.
Syntax
(list-defrules [<module-name>])
If <module-name> is unspecified, then the names of all defrules in the current module are
displayed. If <module-name> is specified, then the names of all defrules in the specified module
are displayed. If <module-name> is the symbol *, then the names of all defrules in all modules
are displayed. This function has no return value.
13.6.3 Deleting a Defrule
This function deletes a previously defined defrule.
Syntax
(undefrule <defrule-name>)
If the defrule is in use (for example if it is firing), then the deletion will fail. If the symbol * is
used for <defrule-name>, then all defrule will be deleted (unless there is a defrule named *). This
function has no return value.
13.6.4 Displaying Matches for a Rule
For a specified rule, displays the list of the facts or instances which match each pattern in the
rule’s LHS, the partial matches for the rule, and the activations for the rule. When listed as a
partial match, the not, exists, and forall CEs are shown as an asterisk. Other CEs contained
within these CEs are not displayed as part of the information shown for a partial match. This
function returns FALSE if the specified rule does not exist or the function is passed invalid
arguments, otherwise a multifield value is returned containing three values: the combined sum of
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the matches for each pattern, the combined sum of partial matches, and the number of
activations.
Syntax
(matches <rule-name> [<verbosity>])
where <verbosity> is either verbose, succinct, or terse. If <verbosity> is not specified or
<verbosity> is verbose, then output will include details for each match, partial match, and
activation. If <verbosity> is succinct, then output will just include the total number of matches,
partial matches, and activations. If <verbosity> is terse, no output will be displayed.
Example
The rule matches-example-1 has three patterns and none are added by CLIPS. Fact f-1 matches
the first pattern, facts f-2 and f-3 match the the second pattern, and fact f-4 matches the third
pattern. Issuing the run command will remove all of the rule’s activations from the agenda.
CLIPS> (clear)
CLIPS>
(defrule matches-example-1
(a ?)
(b ?)
(c ?)
=>)
CLIPS> (reset)
CLIPS> (assert (a 1) (b 1) (b 2) (c 1))
<Fact-4>
CLIPS> (facts)
f-0 (initial-fact)
f-1 (a 1)
f-2 (b 1)
f-3 (b 2)
f-4 (c 1)
For a total of 5 facts.
CLIPS> (run)
CLIPS>
The rule matches-example-2 has three patterns. There are no matches for the first pattern (since
there are no d facts), facts f-2 and f-3 match the third pattern, and fact f-4 matches the forth
pattern.
CLIPS>
(defrule matches-example-2
(not (d ?))
(exists (b ?x)
(c ?x))
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=>)
CLIPS>
Listing the matches for the rule matches-example-1 displays the matches for the patterns
indicated previously. There are two partial matches which satisfy the first two patterns and two
partial matches which satisfy all three patterns. Since all of the rule’s activations were allowed to
fire there are none listed.
CLIPS> (matches matches-example-1)
Matches for Pattern 1
f-1
Matches for Pattern 2
f-2
f-3
Matches for Pattern 3
f-4
Partial matches for CEs 1 - 2
f-1,f-3
f-1,f-2
Partial matches for CEs 1 - 3
f-1,f-2,f-4
f-1,f-3,f-4
Activations
None
(4 4 0)
CLIPS>
Listing the matches for the rule matches-example-2 displays the matches for the patterns
indicated previously. There is one partial match which satisfies the first two CEs (the not pattern
and the exists CE). The * indicates an existential match that is not associated with specific
facts/instances (e.g. the not CE is satisfied because there are no d facts matching the pattern so *
is used to indicate a match as there’s no specific fact matching that pattern). Since none of the
rule’s activations were allowed to fire they are listed. The list of activations will always be a
subset of the partial matches for all of the rule’s CEs.
CLIPS> (matches matches-example-2)
Matches for Pattern 1
None
Matches for Pattern 2
f-2
f-3
Matches for Pattern 3
f-4
Partial matches for CEs 1 - 2
*,f-2
*,f-3
Partial matches for CEs 1 - 3
*,f-2,f-4
Partial matches for CEs 1 (P1) , 2 (P2 - P3)
*,*
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Activations
*,*
(3 4 1)
CLIPS>
If you just want a summary of the partial matches, specify succinct or terse as the second
argument to the function.
CLIPS> (matches matches-example-2 succinct)
Pattern 1: 0
Pattern 2: 2
Pattern 3: 1
CEs 1 - 2: 2
CEs 1 - 3: 1
CEs 1 (P1) , 2 (P2 - P3): 1
Activations: 1
(3 4 1)
CLIPS> (matches matches-example-2 terse)
(3 4 1)
CLIPS>
13.6.5 Setting a Breakpoint for a Rule
Sets a breakpoint for a given rule.
Syntax
(set-break <rule-name>)
If a breakpoint is set for a given rule, execution will stop prior to executing that rule. At least one
rule must fire before a breakpoint will stop execution. This function has no return value.
13.6.6 Removing a Breakpoint for a Rule
Removes a breakpoint for a given rule.
Syntax
(remove-break [<defrule-name>])
If no argument is given, then all breakpoints are removed. This function has no return value.
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13.6.7 Displaying Rule Breakpoints
This command displays all the rules which have breakpoints set. This function has no return
value.
Syntax
(show-breaks [<module-name>])
If <module-name> is unspecified, then the names of all rules having breakpoints in the current
module are displayed. If <module-name> is specified, then the names of all rules having
breakpoints in the specified module are displayed. If <module-name> is the symbol *, then the
names of all rules having breakpoints in all modules are displayed.
13.6.8 Refreshing a Rule
Places all current activations of a given rule on the agenda. This function has no return value.
Syntax
(refresh <rule-name>)
13.6.9 Setting the Incremental Reset Behavior
This function sets the incremental reset behavior. When this behavior is enabled (TRUE by
default), newly defined rules are updated based upon the current state of the fact-list. When
disabled (FALSE), newly defined rules are only updated by facts added after the rule is defined.
In order to prevent rules from obtaining an inconsistent state, the incremental reset behavior can
only be changed when there are no rules currently defined. The return value for this function is
the old value for the behavior.
Syntax
(set-incremental-reset <boolean-expression>)
13.6.10 Getting the Incremental Reset Behavior
This function returns the current value of the incremental reset behavior (TRUE or FALSE).
Syntax
(get-incremental-reset)
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13.6.11 Determining the Logical Dependencies of a Pattern Entity
The dependencies function lists the partial matches from which a pattern entity receives logical
support. This function has no return value.
Syntax
(dependencies <fact-or-instance-specifier>)
The term <fact-or-instance-specifier> includes variables bound on the LHS to fact-addresses or
instance-addresses as described in section 5.4.1.8, the fact-index of the desired fact (e.g. 3 for the
fact labeled f-3), or the instance-name (e.g. [object]).
Example
(defrule list-dependencies
?f <- (factoid $?)
=>
(dependencies ?f))
13.6.12 Determining the Logical Dependents of a Pattern Entity
The dependents function lists all pattern entities which receive logical support from a pattern
entity. This function has no return value.
Syntax
(dependents <fact-or-instance-specifier>)
The term <fact-or-instance-specifier> includes variables bound on the LHS to fact-addresses or
instance-addresses as described in section 5.4.1.8, the fact-index of the desired fact (e.g. 3 for the
fact labeled f-3), or the instance-name (e.g. [object]).
Example
(defrule list-dependents
?f <- (factoid $?)
=>
(dependents ?f))
13.7 Agenda Commands
The following commands manipulate agenda.
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13.7.1 Displaying the Agenda
Displays all activations on the agenda. This function has no return value.
Syntax
(agenda [<module-name>])
If <module-name> is unspecified, then all activations in the current module (not the current
focus) are displayed. If <module-name> is specified, then all activations on the agenda of the
specified module are displayed. If <module-name> is the symbol *, then the activations on all
agendas in all modules are displayed.
13.7.2 Running CLIPS
Starts execution of the rules. If the optional first argument is positive, execution will cease after
the specified number of rule firings or when the agenda contains no rule activations. If there are
no arguments or the first argument is a negative integer, execution will cease when the agenda
contains no rule activations. If the focus stack is empty, then the MAIN module is automatically
becomes the current focus. The run command has no additional effect if evaluated while rules
are executing. Note that the number of rules fired and timing information is no longer printed
after the completion of the run command unless the statistics item is being watched (see section
13.2). If the rules item is being watched, then an informational message will be printed each time
a rule is fired. This function has no return value.
Syntax
(run [<integer-expression>])
13.7.3 Focusing on a Group of Rules
Pushes one or more modules onto the focus stack. The specified modules are pushed onto the
focus stack in the reverse order they are listed. The current module is set to the last module
pushed onto the focus stack. The current focus is the top module of the focus stack. Thus (focus
A B C) pushes C, then B, then A unto the focus stack so that A is now the current focus. Note
that the current focus is different from the current module. Focusing on a module implies
“remembering” the current module so that it can be returned to later. Setting the current module
with the set-current-module function changes it without remembering the old module. Before a
rule executes, the current module is changed to the module in which the executing rule is defined
(the current focus). This function returns a boolean value: FALSE if an error occurs, otherwise
TRUE.
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Syntax
(focus <module-name>+)
13.7.4 Stopping Rule Execution
The halt function may be used on the RHS of a rule to prevent further rule firing. It is called
without arguments. After halt is called, control is returned from the run command. The agenda
is left intact, and execution may be continued with a run command. This function has no return
value.
Syntax
(halt)
13.7.5 Setting The Current Conflict Resolution Strategy
This function sets the current conflict resolution strategy. The default strategy is depth.
Syntax
(set-strategy <strategy>)
where <strategy> is either depth, breadth, simplicity, complexity, lex, mea, or random. The old
conflict resolution strategy is returned. The agenda will be reordered to reflect the new conflict
resolution strategy.
13.7.6 Getting The Current Conflict Resolution Strategy
This function returns the current conflict resolution strategy (depth, breadth, simplicity,
complexity, lex, mea, or random).
Syntax
(get-strategy)
13.7.7 Listing the Module Names on the Focus Stack
The command list-focus-stack list all module names on the focus stack. The first name listed is
the current focus.
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Syntax
(list-focus-stack)
13.7.8 Removing all Module Names from the Focus Stack
The command clear-focus-stack removes all module names from the focus stack.
Syntax
(clear-focus-stack)
13.7.9 Setting the Salience Evaluation Behavior
This function sets the salience evaluation behavior. By default, salience values are only
evaluated when a rule is defined.
Syntax
(set-salience-evaluation <value>)
where <value> is either when-defined, when-activated, or every-cycle. The return value for this
function is the old value for salience evaluation. The value when-defined forces salience
evaluation at the time of rule definition. The value when-activation forces salience evaluation at
the time of rule definition and upon being activated. The value every-cycle forces evaluation at
the time of rule definition, upon being activated, and after every rule firing.
13.7.10 Getting the Salience Evaluation Behavior
This function returns the current salience evaluation behavior (when-defined, when-activated, or
every-cycle).
Syntax
(get-salience-evaluation)
13.7.11 Refreshing the Salience Value of Rules on the Agenda
This function forces reevaluation of saliences of rules on the agenda regardless of the current
salience evaluation setting. This function has no return value.
Syntax
(refresh-agenda [<module-name>])
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If <module-name> is unspecified, then the agenda in the current module is refreshed. If
<module-name> is specified, then the agenda in the specified module is refreshed. If
<module-name> is the symbol *, then the agenda in every module is refreshed.
13.8 Defglobal Commands
The following commands manipulate defglobals.
13.8.1 Displaying the Text of a Defglobal
Displays the text required to define a given global variable. Note that unlike other constructs
such as deffacts and definstances, defglobal definitions have no name associated with the entire
construct. The variable name passed to ppdefglobal should not include the question mark or the
asterisks (e.g. x is the variable name for the global variable ?*x*). This function has no return
value.
Syntax
(ppdefglobal <global-variable-name>)
13.8.2 Displaying the List of Defglobals
Displays the names of all defglobals. This function has no return value.
Syntax
(list-defglobals [<module-name>])
If <module-name> is unspecified, then the names of all defglobals in the current module are
displayed. If <module-name> is specified, then the names of all defglobals in the specified
module are displayed. If <module-name> is the symbol *, then the names of all defglobals in all
modules are displayed.
13.8.3 Deleting a Defglobal
This function deletes a previously defined defglobal.
Syntax
(undefglobal <defglobal-name>)
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If the defglobal is in use (for example if it is referred to in a deffunction), then the deletion will
fail. Otherwise, no further uses of the deleted defglobal are permitted (unless redefined). If the
symbol * is used for <defglobal-name>, then all defglobals will be deleted (unless there is a
defglobal named *). This function has no return value.
13.8.4 Displaying the Values of Global Variables
Displays the names and current values of all defglobals. This function has no return value.
Syntax
(show-defglobals [<module-name>])
If <module-name> is unspecified, then the names and values of all defglobals in the current
module are displayed. If <module-name> is specified, then the names and values of all
defglobals in the specified module are displayed. If <module-name> is the symbol *, then the
names and values of all defglobals in all modules are displayed.
13.8.5 Setting the Reset Behavior of Global Variables
This function sets the reset global variables behavior. When this behavior is enabled (TRUE by
default) global variables are reset to their original values when the reset command is performed.
The return value for this function is the old value for the behavior.
Syntax
(set-reset-globals <boolean-expression>)
13.8.6 Getting the Reset Behavior of Global Variables
This function returns the current value of the reset global variables behavior (TRUE or FALSE).
Syntax
(get-reset-globals)
13.9 Deffunction Commands
The following commands manipulate deffunctions.
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13.9.1 Displaying the Text of a Deffunction
Displays the text of a given deffunction. This function has no return value.
Syntax
(ppdeffunction <deffunction-name>)
13.9.2 Displaying the List of Deffunctions
Displays the names of all deffunctions stored in the CLIPS environment. This function has no
return value.
Syntax
(list-deffunctions)
13.9.3 Deleting a Deffunction
This function deletes a previously defined deffunction.
Syntax
(undeffunction <deffunction-name>)
If the symbol * is used for <deffunction-name>, then all deffunctions will be deleted (unless
there exists a deffunction called *). The undeffunction command can be used to remove
deffunctions at any time. Exceptions: A deffunction may not be deleted when it is executing or
when there is still a reference to it in another loaded construct, such as a rule RHS. This function
has no return value.
13.10 Generic Function Commands
The following commands manipulate generic functions.
13.10.1 Displaying the Text of a Generic Function Header
Displays the text of a given generic function header. This function has no return value.
Syntax
(ppdefgeneric <generic-function-name>)
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13.10.2 Displaying the Text of a Generic Function Method
Displays the text of a given method.
Syntax
(ppdefmethod <generic-function-name> <index>)
where <index> is the method index (see section 8.4.2). This function has no return value.
13.10.3 Displaying the List of Generic Functions
Displays the names of all generic functions stored in the CLIPS environment.
Syntax
(list-defgenerics [<module-name>])
If <module-name> is unspecified, then the names of all defgenerics in the current module are
displayed. If <module-name> is specified, then the names of all defgenerics in the specified
module are displayed. If <module-name> is the symbol *, then the names of all defgenerics in all
modules are displayed. This function has no return value.
13.10.4 Displaying the List of Methods for a Generic Function
If no name is given, this function lists all generic function methods in the CLIPS environment. If
a name is given, then only the methods for the named generic function are listed. The methods
are listed in decreasing order of precedence (see section 8.5.2) for each generic function. Method
indices can be seen using this function. This function has no return value.
Syntax
(list-defmethods [<generic-function-name>])
13.10.5 Deleting a Generic Function
This function deletes a previously defined generic function.
Syntax
(undefgeneric <generic-function-name>)
If the symbol * is used for <generic-function-name>, then all generic functions will be deleted
(unless there exists a generic function called *). This function removes the header and all
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methods for a generic function. The undefgeneric command can be used to remove generic
functions at any time. Exceptions: A generic function may not be deleted when any of its
methods are executing or when there is still a reference to it in another loaded construct, such as
a rule RHS. This function has no return value.
13.10.6 Deleting a Generic Function Method
This function deletes a previously defined generic function method.
Syntax
(undefmethod <generic-function-name> <index>)
where <index> is the index of the method to be deleted for the generic function. If the symbol *
is used for <index>, then all the methods for the generic function will be deleted. (This is
different from the undefgeneric command because the header is not removed.) If * is used for
<generic-function-name>, then * must also be specified for <index>, and all the methods for all
generic functions will be removed. This function removes the specified method for a generic
function, but even if the method removed is the last one, the generic function header is not
removed. The undefmethod command can be used to remove methods at any time. Exceptions: A
method may not be deleted when it or any of the other methods for the same generic function are
executing. This function has no return value.
13.10.7 Previewing a Generic Function Call
This debugging function lists all applicable methods for a particular generic function call in
order of decreasing precedence (see section 8.5.2). The function list-defmethods is different in
that it lists all methods for a generic function.
Syntax
(preview-generic <generic-function-name> <expression>*)
This function does not actually execute any of the methods, but any side-effects of evaluating the
generic function arguments and any query parameter restrictions (see section 8.4.3) in methods
do occur. The output for the first example in section 8.5.2 would be as follows:
Example
CLIPS> (preview-generic + 4 5)
+ #7 (INTEGER <qry>) (INTEGER <qry>)
+ #8 (INTEGER <qry>) (NUMBER)
+ #3 (INTEGER) (INTEGER)
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+ #4 (INTEGER) (NUMBER)
+ #6 (NUMBER) (INTEGER <qry>)
+ #2 (NUMBER) (INTEGER)
+ #SYS1 (NUMBER) (NUMBER) ($? NUMBER)
+ #5 (NUMBER) (NUMBER) ($? PRIMITIVE)
CLIPS>
13.11 CLIPS Object-Oriented Language (COOL) Commands
The following commands manipulate elements of COOL.
13.11.1 Class Commands
The following commands manipulate defclasses.
13.11.1.1 Displaying the Text of a Defclass
Displays the text of a given defclass. This function has no return value.
Syntax
(ppdefclass <class-name>)
13.11.1.2 Displaying the List of Defclasses
Displays the names of all defclasses stored in the CLIPS environment. If <module-name> is
unspecified, then the names of all defclasses in the current module are displayed. If
<module-name> is specified, then the names of all defclasses in the specified module are
displayed. If <module-name> is the symbol *, then the names of all defclasses in all modules are
displayed. This function has no return value.
Syntax
(list-defclasses [<module-name>])
13.11.1.3 Deleting a Defclass
This function deletes a previously defined defclass and all its subclasses from the CLIPS
environment.
Syntax
(undefclass <class-name>)
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If the symbol * is used for <class-name>, then all defclasses will be deleted (unless there exists a
defclass called *). The undefclass command can be used to remove defclasses at any time.
Exceptions: A defclass may not be deleted if it has any instances or if there is still a reference to
it in another loaded construct, such as a generic function method. This function has no return
value.
13.11.1.4 Examining a Class
This function provides a verbose description of a class including: abstract role (whether direct
instances can be created or not), direct superclasses and subclasses, class precedence list, slots
with all their facets and sources, and all recognized message-handlers. This function has no
return value.
Syntax
(describe-class <class-name>)
Example
CLIPS>
(defclass CHILD (is-a USER)
(role abstract)
(multislot parents (cardinality 2 2))
(slot age (type INTEGER)
(range 0 18))
(slot sex (access read-only)
(type SYMBOL)
(allowed-symbols male female)
(storage shared)))
CLIPS>
(defclass BOY (is-a CHILD)
(slot sex (source composite)
(default male)))
CLIPS>
(defmessage-handler BOY play ()
(printout t "The boy is now playing..." crlf))
CLIPS> (describe-class CHILD)
================================================================================
********************************************************************************
Abstract: direct instances of this class cannot be created.
Direct Superclasses: USER
Inheritance Precedence: CHILD USER OBJECT
Direct Subclasses: BOY
--------------------------------------------------------------------------------
SLOTS : FLD DEF PRP ACC STO MCH SRC VIS CRT OVRD-MSG SOURCE(S)
parents : MLT STC INH RW LCL RCT EXC PRV RW put-parents CHILD
age : SGL STC INH RW LCL RCT EXC PRV RW put-age CHILD
sex : SGL STC INH R SHR RCT EXC PRV R NIL CHILD
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Constraint information for slots:
SLOTS : SYM STR INN INA EXA FTA INT FLT
parents : + + + + + + + + RNG:[-oo..+oo] CRD:[2..2]
age : + RNG:[0..18]
sex : #
--------------------------------------------------------------------------------
Recognized message-handlers:
init primary in class USER
delete primary in class USER
create primary in class USER
print primary in class USER
direct-modify primary in class USER
message-modify primary in class USER
direct-duplicate primary in class USER
message-duplicate primary in class USER
get-parents primary in class CHILD
put-parents primary in class CHILD
get-age primary in class CHILD
put-age primary in class CHILD
get-sex primary in class CHILD
********************************************************************************
================================================================================
CLIPS>
The following table explains the fields and their possible values in the slot descriptions:
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Field
Values
Explanation
FLD
SGL/MLT
Field type (single-field or multifield)
DEF
STC/DYN/NIL
Default value (static, dynamic, or none)
PRP
INH/NIL
Propagation to subclasses (inheritable or not
inheritable)
ACC
RW/R/INT
Access (read-write, read-only, or initialize-only)
STO
LCL/SHR
Storage (local or shared)
MCH
RCT/NIL
Pattern-match (reactive or non-reactive)
SRC
CMP/EXC
Source type (composite or exclusive)
VIS
PUB/PRV
Visibility (public or private)
CRT
R/W/RW/NIL
Automatically created accessors (read, write,
read-write, or none)
OVRD-MSG
<message-name>
Name of message sent for slot-overrides in
make-instance, etc.
SOURCE(S)
<class-name>+
Source of slot (more than one class for
composite)
In the constraint information summary for the slots, each of the columns shows one of the
primitive data types . A + in the column means that any value of that type is allowed in the slot.
A # in the column means that some values of that type are allowed in the slot. Range and
cardinality constraints are displayed to the far right of each slot's row. The following table
explains the abbreviations used in the constraint information summary for the slots:
Abbreviation
Explanation
SYM
Symbol
STR
String
INN
Instance Name
INA
Instance Address
EXA
External Address
FTA
Fact Address
INT
Integer
FLT
Float
RNG
Range
CRD
Cardinality
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13.11.1.5 Examining the Class Hierarchy
This function provides a rudimentary display of the inheritance relationships between a class and
all its subclasses. Indentation indicates a subclass. Because of multiple inheritance, some classes
may appear more than once. Asterisks mark classes which are direct subclasses of more than one
class. With no arguments, this function starts with the root class OBJECT. This function has no
return value.
Syntax
(browse-classes [<class-name>])
Example
CLIPS> (clear)
CLIPS> (defclass A (is-a USER))
CLIPS> (defclass B (is-a USER))
CLIPS> (defclass C (is-a A B))
CLIPS> (defclass D (is-a USER))
CLIPS> (defclass E (is-a C D))
CLIPS> (defclass F (is-a E))
CLIPS> (browse-classes)
OBJECT
PRIMITIVE
NUMBER
INTEGER
FLOAT
LEXEME
SYMBOL
STRING
MULTIFIELD
ADDRESS
EXTERNAL-ADDRESS
FACT-ADDRESS
INSTANCE-ADDRESS *
INSTANCE
INSTANCE-ADDRESS *
INSTANCE-NAME
USER
INITIAL-OBJECT
A
C *
E *
F
B
C *
E *
F
D
E *
F
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CLIPS>
13.11.2 Message-handler Commands
The following commands manipulate defmessage-handlers.
13.11.2.1 Displaying the Text of a Defmessage-handler
Displays the text of a given defmessage-handler. This function has no return value.
Syntax
Defaults are in bold italics.
(ppdefmessage-handler <class-name> <handler-name>
[<handler-type>])
<handler-type> ::= around | before |
primary
| after
13.11.2.2 Displaying the List of Defmessage-handlers
With no arguments, this function lists all handlers in the system. With one argument, this
function lists all handlers for the specified class. If the optional argument “inherit” is given,
inherited message-handlers are also included. This function has no return value.
Syntax
(list-defmessage-handlers [<class-name> [inherit]])
Example
List all primary handlers in the system.
CLIPS> (clear)
CLIPS> (defclass A (is-a USER))
CLIPS> (defmessage-handler A foo ())
CLIPS> (list-defmessage-handlers A)
foo primary in class A
For a total of 1 message-handler.
CLIPS> (list-defmessage-handlers A inherit)
init primary in class USER
delete primary in class USER
create primary in class USER
print primary in class USER
direct-modify primary in class USER
message-modify primary in class USER
direct-duplicate primary in class USER
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message-duplicate primary in class USER
foo primary in class A
For a total of 9 message-handlers.
CLIPS>
13.11.2.3 Deleting a Defmessage-handler
This function deletes a previously defined message-handler.
Syntax
Defaults are in bold italics.
(undefmessage-handler <class-name> <handler-name>
[<handler-type>])
<handler-type> ::= around | before |
primary
| after
An asterisk can be used to specify a wildcard for any of the arguments. (Wildcards will not work
for the class name or handler name if there is a class or handler called *.) The
undefmessage-handler command can be used to remove handlers at any time. Exceptions: A
handler may not be deleted when it or any of the other handlers for the same class are executing.
This function has no return value.
Example
Delete all primary handlers in the system.
CLIPS> (undefmessage-handler * *)
CLIPS>
13.11.2.4 Previewing a Message
Displays a list of all the applicable message-handlers for a message sent to an instance of a
particular class. The level of indentation indicates the number of times a handler is shadowed,
and lines connect the beginning and ending portions of the execution of a handler if it encloses
shadowed handlers. The right double-angle brackets indicate the beginning of handler execution,
and the left double-angle brackets indicate the end of handler execution. Message arguments are
not necessary for a preview since they do not dictate handler applicability.
Syntax
(preview-send <class-name> <message-name>)
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Example
For the example in section 9.5.3, the output would be:
CLIPS> (preview-send USER my-message)
>> my-message around in class USER
| >> my-message around in class OBJECT
| | >> my-message before in class USER
| | << my-message before in class USER
| | >> my-message before in class OBJECT
| | << my-message before in class OBJECT
| | >> my-message primary in class USER
| | | >> my-message primary in class OBJECT
| | | << my-message primary in class OBJECT
| | << my-message primary in class USER
| | >> my-message after in class OBJECT
| | << my-message after in class OBJECT
| | >> my-message after in class USER
| | << my-message after in class USER
| << my-message around in class OBJECT
<< my-message around in class USER
CLIPS>
13.11.3 Definstances Commands
The following commands manipulate definstances.
13.11.3.1 Displaying the Text of a Definstances
Displays the text of a given definstances. This function has no return value.
Syntax
(ppdefinstances <definstances-name>)
13.11.3.2 Displaying the List of Definstances
Displays the names of all definstances stored in the CLIPS environment. This function has no
return value.
Syntax
(list-definstances)
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13.11.3.3 Deleting a Definstances
This function deletes a previously defined definstances.
Syntax
(undefinstances <definstances-name>)
If the symbol * is used for <definstances-name>, then all definstances will be deleted (unless
there exists a definstances called *). The undefinstances command can be used to remove
definstances at any time. Exceptions: A definstances may not be deleted when any of the
instances in it are being created. This function has no return value.
13.11.4 Instances Commands
The following commands manipulate instances of user-defined classes.
13.11.4.1 Listing the Instances
If no arguments are specified, all instances in scope of the current module are listed. If a module
name is given, all instances within the scope of that module are given. If “*” is specified (and
there is no module named “*”), all instances in all modules are listed (only instances which
actually belong to classes of a module are listed for each module to prevent duplicates). If a class
name is specified, only the instances for the named class are listed. If a class is specified, then
the optional keyword inherit causes this function to list instances of subclasses of the class as
well. This function has no return value.
Syntax
(instances [<module-name> [<class-name> [inherit]]])
13.11.4.2 Printing an Instance’s Slots from a Handler
This function operates implicitly on the active instance (see section 9.4.1.1) for a message, and
thus can only be called from within the body of a message-handler. This function directly prints
the slots of the active instance and is the one used to implement the print handler attached to
class USER (see section 9.4.4.3). This function has no return value.
Syntax
(ppinstance)
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13.11.4.3 Saving Instances to a Text File
This function saves all instances in the CLIPS environment to the specified file in the following
format:
(<instance-name> of <class-name> <slot-override>*)
<slot-override> ::= (<slot-name> <single-field-value>*)
A slot-override is generated for every slot of every instance, regardless of whether the slot
currently holds a default value or not. External-address and fact-address slot values are saved as
strings. Instance-address slot values are saved as instance-names. This function returns the
number of instances saved.
Syntax
(save-instances <file-name>
[local | visible [[inherit] <class>+])
By default, save-instances saves only the instances of all defclasses in the current module.
Specifying visible saves instances for all classes within scope of the current module. Also,
particular classes may be specified for saving, but they must be in scope according to the local or
visible option. The inherit keyword can be used to force the saving of indirect instances of
named classes as well (by default only direct instances are saved for named classes). Subclasses
must still be in local or visible scope in order for their instances to be saved. Unless the inherit
option is specified, only concrete classes can be specified. At least one class is required for the
inherit option.
The file generated by this function can be loaded by either load-instances or restore-instances.
save-instances does not preserve module information, so the instance file should be loaded into
the module which was current when it was saved.
13.11.4.4 Saving Instances to a Binary File
The function bsave-instances works exactly like save-instances except that the instances are
saved in a binary format which can only be loaded with the function bload-instances. The
advantage to this format is that loading binary instances can be much faster than loading text
instances for large numbers of instances. The disadvantage is that the file is not usually portable
to other platforms.
Syntax
(bsave-instances <file-name>
[local | visible [[inherit] <class>+])
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13.11.4.5 Loading Instances from a Text File
This function loads instances from a file into the CLIPS environment. It can read files created
with save-instances or any ASCII text file. Each instance should be in the format described in
section 13.11.4.3 (although the instance name can be left unspecified). Calling load-instances is
exactly equivalent to a series of make-instance calls (in CLIPS version 5.1, slot access
restrictions, such as read-only, were suspended during calls to load-instances). This function
returns the number of instances loaded or -1 if it could not access the instance file.
Syntax
(load-instances <file-name>)
13.11.4.6 Loading Instances from a Text File without Message Passing
The function restore-instances loads instances from a file into the CLIPS environment. It can
read files created with save-instances or any ASCII text file. Each instance should be in the
format described in section 13.11.4.3 (although the instance name can be left unspecified). It is
similar in operation to load-instances, however, unlike load-instances, restore-instances does not
use message-passing for deletions, initialization, or slot-overrides. Thus in order to preserve
object encapsulation, it is recommended that restore-instances only be used with files generated
by save-instances. This function returns the number of instances loaded or -1 if it could not
access the instance file.
Syntax
(restore-instances <file-name>)
13.11.4.7 Loading Instances from a Binary File
This function is similar to restore-instances except that it can only work with files generated by
bsave-instances. See section 13.11.4.4 for a discussion of the merits of using binary instance
files.
Syntax
(bload-instances <file-name>)
13.12 Defmodule Commands
The following commands manipulate defmodule constructs.
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13.12.1 Displaying the Text of a Defmodule
Displays the text of a given defmodule. This function has no return value.
Syntax
(ppdefmodule <defmodule-name>)
13.12.2 Displaying the List of Defmodules
Displays the names of all defmodule constructs stored in the CLIPS environment. This function
has no return value.
Syntax
(list-defmodules)
13.13 Memory Management Commands
The following commands display CLIPS memory status information. CLIPS memory
management is described more fully in the Advanced Programming Guide.
13.13.1 Determining the Amount of Memory Used by CLIPS
Returns an integer representing the number of bytes CLIPS has currently in-use or has held for
later use. This number does not include operating system overhead for allocating memory.
Syntax
(mem-used)
13.13.2 Determining the Number of Memory Requests Made by CLIPS
Returns an integer representing the number of times CLIPS has requested memory from the
operating system. If the operating system overhead for allocating memory is known, then the
total memory used can be calculated by
(+ (mem-used) (* <overhead-in-bytes> (mem-requests)))
Syntax
(mem-requests)
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13.13.3 Releasing Memory Used by CLIPS
Releases all free memory held internally by CLIPS back to the operating system. CLIPS will
automatically call this function if it is running low on memory to allow the operating system to
coalesce smaller memory blocks into larger ones. This function generally should not be called
unless the user knows exactly what he/she is doing (since calling this function can prevent
CLIPS from reusing memory efficiently and thus slow down performance). This function returns
an integer representing the amount of memory freed to the operating system.
Syntax
(release-mem)
13.13.4 Conserving Memory
Turns on or off the storage of information used for save and pretty print commands. This can
save considerable memory in a large system. It should be called prior to loading any constructs.
This function has no return value.
Syntax
(conserve-mem <value>)
where value is either on or off.
13.14 External Text Manipulation
CLIPS provides a set of functions to build and access a hierarchical lookup system for multiple
external files. Each file contains a set of text entries in a special format that CLIPS can later
reference and display. The basic concept is that CLIPS retains a “map” of the text file in memory
and can easily pull sections of text from the file without having to store the whole file in memory
and without having to sequentially search the file for the appropriate text.
13.14.1 External Text File Format
Each external text file to be loaded into CLIPS must be described in a particular way. Each topic
entry in each file must be in the format shown following.
Syntax
<level-num> <entry-type> BEGIN-ENTRY- <topic-name>
•
•
Topic information in form to be displayed when referenced.
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•
•
END-ENTRY
The delimiter strings (lines with BEGIN_ENTRY or END_ENTRY info) must be the only things
on their lines. Embedded white space between the fields of the delimiters is allowed.
The first parameter, <level-num>, is the level of the hierarchical tree to which the entry belongs.
The lower the number, the closer to the root level the topic is; i.e., the lowest level number
indicates the root level. Subtopics are indicated by making the level number of the current topic
larger than the previous entry (which is to be the parent). Thus, the tree must be entered in the
file sequentially; i.e., a topic with all its subtopics must be described before going on to a topic at
the same level. Entering a number less than that of the previous topic will cause the tree to be
searched upwards until a level number is found which is less than the current one. The current
topic then will be attached as a subtopic at that level. In this manner, multiple root trees may be
created. Level number and order of entry in a file can indicate the order of precedence in which a
list of subtopics that are all children of the same topic will be searched. Topics with the same
level number will be searched in the order in which they appear in the file. Topics with
lower-level numbers will be searched first.
Example
0MBEGIN-ENTRY-ROOT
-- Text --
END-ENTRY
2IBEGIN-ENTRY-SUBTOPIC1
-- Text --
END-ENTRY
1IBEGIN-ENTRY-SUBTOPIC2
-- Text --
END-ENTRY
In the above example, SUBTOPIC1 and SUBTOPIC2 are children of ROOT. However, in
searching the children of ROOT, SUBTOPIC2 would be found first.
The second parameter in the format defined above, the <entry-type>, must be a single capital
letter, either M (for MENU) or I (for INFORMATION). Only MENU entries may have
subtopics.
The third parameter defined above, the <topic-name>, can be any alphanumeric string of up to
80 characters. No white space can be embedded in the name.
Beginning a line with the delimiter “$$” forces the loader to treat the line as pure text, even if
one of the key delimiters is in it. When the line is printed, the dollar signs are treated as blanks.
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Example
0MBEGIN-ENTRY-ROOT1
-- Root1 Text --
END-ENTRY
1MBEGIN-ENTRY-SUBTOPIC1
-- Subtopic1 Text --
END-ENTRY
2IBEGIN-ENTRY-SUBTOPIC4
-- Subtopic4 Text --
END-ENTRY
1IBEGIN-ENTRY-SUBTOPIC2
-- Subtopic2 Text --
END-ENTRY
0IBEGIN-ENTRY-ROOT2
-- Root2 Text --
END-ENTRY
-1MBEGIN-ENTRY-ROOT3
-- Root3 Text --
END-ENTRY
0IBEGIN-ENTRY-SUBTOPIC3
-- Subtopic3 Text --
END-ENTRY
Tree Diagram of Above Example :
-> ROOT3 ---------> ROOT1 ---------> ROOT2
| / \
| / \
V V V
SUBTOPIC3 SUBTOPIC1 SUBTOPIC2
|
|
V
SUBTOPIC4
13.14.2 External Text Manipulation Functions
The following functions can be used by users to maintain their own information system.
13.14.2.1 Fetch
The function fetch loads the named file (which must be in the format defined in section 13.14.1)
into the internal lookup table.
Syntax
(fetch <file-name>)
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The function returns the number of entries loaded if the fetch succeeded. If the file could not be
loaded or was loaded already, the function returns the symbol FALSE.
13.14.2.2 Print-region
The function print-region looks up a specified entry in a particular file which has been loaded
previously into the lookup table and prints the contents of that entry to the specified output.
Syntax
(print-region <logical-name> <file-name> <topic-field>*)
where <logical-name> is a name previously attached to an output device. To send the output to
stdout, specify t for the logical name. <file-name> is the name of the previously loaded file in
which the entry is to be found, and the optional arguments, <topic-field>*, is the full path of the
topic entry to be found.
Each element or field in the path is delimited by white space, and the function is not case
sensitive. In addition, the entire name of a field does not need to be specified. Only enough
characters to distinguish the field from other choices at the same level of the tree are necessary.
If there is a conflict, the function will pick the first one in the list. A few special fields can be
specified.
^ Branch up one level.
? When specified at the end of a path, this forces a display of the current menu, even on
branch-ups.
<nil> Giving no topic field will branch up one level.
The level of the tree for a file remains constant between calls to print-region. All levels count
from menu only. Information levels do not count for branching up or down. To access an entry at
the root level after branching down several levels in a previous call or series of calls, an equal
number of branches up must be executed.
Examples
To display the entry for ROOT SUBTOPIC from the file foo.lis on the screen, type
(print-region t "foo.lis" ROOT SUBTOPIC)
or, using less characters,
(print-region t "foo.lis" roo sub)
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Only one entry can be accessed per print-region call. The function returns the symbol TRUE if
the print-region succeeded. If the entry was not found, it returns FALSE.
CLIPS> (fetch "foo.lis")
7
CLIPS> (print-region t "foo.lis" roo sub)
-- Subtopic3 Text --
TRUE
CLIPS> (print-region t "foo.lis" "?")
-- Root3 Text --
TRUE
CLIPS> (print-region t "foo.lis" ^ root1 sub)
-- Subtopic1 Text --
TRUE
CLIPS> (print-region t "foo.lis" sub)
-- Subtopic4 Text --
TRUE
CLIPS> (print-region t "foo.lis" ^ subtopic2)
-- Subtopic2 Text --
TRUE
CLIPS> (print-region t "foo.lis" ^ root2)
-- Root2 Text --
TRUE
CLIPS> (toss "foo.lis")
TRUE
CLIPS>
13.14.2.3 Get-region
The function get-region looks up a specified entry in a particular file which has been loaded
previously into the lookup table and returns the contents of that entry as a string.
Syntax
(get-region <file-name> <topic-field>*)
where <file-name> is the name of the previously loaded file in which the entry is to be found,
and the optional arguments, <topic-field>*, is the full path of the topic entry to be found. The
get-region the print-region functions share the same behavior for the special topic fields and
maintaining the level of the tree for a file between function calls. If an error occurs, this function
returns an empty string.
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13.14.2.4 Toss
The function toss unloads the named file from the internal lookup table and releases the memory
back to the system.
Syntax
(toss <file-name>)
The function returns the symbol TRUE if the toss succeeded. If the file was not on the lookup
table, it returns FALSE.
13.15 Profiling Commands
The following commands provide the ability to profile CLIPS programs for performance.
13.15.1 Setting the Profiling Report Threshold
The set-profile-percent-threshold command sets the minimum percentage of time that must be
spent executing a construct or user function for it to be displayed by the profile-info command.
By default, the percent threshold is zero, so all constructs or user-functions that were profiled
and executed at least once will be displayed by the profile-info command. The return value of
this function is the old percent threshold.
Syntax
(set-profile-percent-threshold <number in the range 0 to 100>)
13.15.2 Getting the Profiling Report Threshold
The get-profile-percent-threshold command returns the current value of the profile percent
threshold.
Syntax
(get-profile-percent-threshold)
13.15.3 Resetting Profiling Information
The profile-reset command resets all profiling information currently collected for constructs and
user functions.
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Section 13: Commands
Syntax
(profile-reset)
13.15.4 Displaying Profiling Information
The profile-info command displays profiling information currently collected for constructs or
user functions. Profiling information is displayed in six columns. The first column contains the
name of the construct or user function profiled. The second column indicates the number of
times the construct or user function was executed. The third column is the amount of time spent
executing the construct or user function. The fourth column is the percentage of time spent in the
construct or user function with respect to the total amount of time profiling was enabled. The
fifth column is the total amount of time spent in the first execution of the construct or user
function and all subsequent calls to other constructs/user functions. The sixth column is the
percentage of this time with respect to the total amount of time profiling was enabled.
Syntax
(profile-info)
13.15.5 Profiling Constructs and User Functions
The profile command is used to enable/disable profiling of constructs and user functions. If
constructs are profiled, then the amount of time spent executing deffunctions, generic functions,
message handlers, and the RHS of defrules is tracked. If user-functions are profiled, then the
time spent executing system and user defined functions is tracked. System defined functions
include predefined functions available for your own use such as the < and numberp functions in
addition to low level internal functions which are not available for your use (these will usually
appear in profile-info output in all capital letters or surrounded by parentheses). It is not possible
to profile constructs and user-functions at the same time. Enabling one disables the other. The off
keyword argument disables profiling. Profiling can be repeatedly enable and disabled as long as
only one of constructs or user-functions is consistently enabled. The total amount of time spent
with profiling enabled will be displayed by the profile-info command. If profiling is enabled
from the command prompt, it is a good idea to place the calls enabling and disabling profiling
within a single progn function call. This will prevent the elapsed profiling time from including
the amount of time needed to type the commands being profiled.
Syntax
(profile constructs | user-functions | off)
Example
CLIPS> (clear)
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CLIPS> (deffacts start (fact 1))
CLIPS>
(deffunction function-1 (?x)
(bind ?y 1)
(loop-for-count (* ?x 10)
(bind ?y (+ ?y ?x))))
CLIPS>
(defrule rule-1
?f <- (fact ?x&:(< ?x 100))
=>
(function-1 ?x)
(retract ?f)
(assert (fact (+ ?x 1))))
CLIPS>
(reset)
CLIPS>
(progn (profile constructs)
(run)
(profile off))
CLIPS> (profile-info)
Profile elapsed time = 0.474921 seconds
Construct Name Entries Time % Time+Kids %+Kids
-------------- ------- ------ ----- --------- ------
*** Deffunctions ***
function-1 99 0.436704 91.92% 0.436704 91.92%
*** Defrules ***
rule-1 99 0.027561 5.80% 0.464265 97.72%
CLIPS> (profile-reset)
CLIPS> (reset)
CLIPS>
(progn (profile user-functions)
(run)
(profile off))
CLIPS> (profile-info)
Profile elapsed time = 12.0454 seconds
Function Name Entries Time % Time+Kids %+Kids
------------- ------- ------ ----- --------- ------
retract 99 0.007953 0.07% 0.010646 0.09%
assert 99 0.012160 0.10% 0.032766 0.27%
run 1 0.047421 0.39% 12.045301 100.00%
profile 1 0.000049 0.00% 0.000049 0.00%
* 99 0.005579 0.05% 0.007610 0.06%
+ 49599 3.626217 30.10% 5.765490 47.86%
< 99 0.005234 0.04% 0.007749 0.06%
progn 49698 2.353003 19.53% 11.997880 99.61%
loop-for-count 99 1.481078 12.30% 11.910553 98.88%
PCALL 99 0.020747 0.17% 11.943234 99.15%
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Section 13: Commands
FACT_PN_VAR3 99 0.002515 0.02% 0.002515 0.02%
FACT_JN_VAR1 99 0.002693 0.02% 0.002693 0.02%
FACT_JN_VAR3 198 0.004718 0.04% 0.004718 0.04%
FACT_STORE_MULTIFIELD 99 0.005478 0.05% 0.012857 0.11%
PROC_PARAM 49599 1.036460 8.60% 1.036460 8.60%
PROC_GET_BIND 49500 1.102682 9.15% 1.102682 9.15%
PROC_BIND 49599 2.331363 19.35% 8.089474 67.16%
CLIPS> (set-profile-percent-threshold 1)
0.0
CLIPS> (profile-info)
Profile elapsed time = 12.0454 seconds
Function Name Entries Time % Time+Kids %+Kids
------------- ------- ------ ----- --------- ------
+ 49599 3.626217 30.10% 5.765490 47.86%
progn 49698 2.353003 19.53% 11.997880 99.61%
loop-for-count 99 1.481078 12.30% 11.910553 98.88%
PROC_PARAM 49599 1.036460 8.60% 1.036460 8.60%
PROC_GET_BIND 49500 1.102682 9.15% 1.102682 9.15%
PROC_BIND 49599 2.331363 19.35% 8.089474 67.16%
CLIPS> (profile-reset)
CLIPS> (profile-info)
CLIPS>
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Appendix A:
Support Information
A.1 Questions and Information
The URL for the CLIPS Web page is http://clipsrules.sourceforge.net.
Questions regarding CLIPS can be posted to one of several online forums including the CLIPS
Expert System Group, http://groups.google.com/group/CLIPSESG/, the SourceForge CLIPS
Forums, http://sourceforge.net/forum/?group_id=215471, and Stack Overflow,
http://stackoverflow.com/questions/tagged/clips.
Inquiries related to the use or installation of CLIPS can be sent via electronic mail to
clipssupport@secretsocietysoftware.com.
A.2 Documentation
The CLIPS Reference Manuals and User’s Guide are available in Portable Document Format
(PDF) at http://clipsrules.sourceforge.net/OnlineDocs.html.
Expert Systems: Principles and Programming, 4th Edition, by Giarratano and Riley comes with
a CD-ROM containing CLIPS 6.22 executables (DOS, Windows XP, and Mac OS),
documentation, and source code. The first half of the book is theory oriented and the second half
covers rule-based, procedural, and object-oriented programming using CLIPS.
A.3 CLIPS Source Code and Executables
CLIPS executables and source code are available on the SourceForge web site at
http://sourceforge.net/projects/clipsrules/files.
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Appendix B:
Update Release Notes
The following sections denote the changes and bug fixes for CLIPS versions 6.2. 6.21, 6.22,
6.23, 6.24, and 6.3.
B.1 Version 6.30
• Performance Improvements – Rule performance has been improved particularly in
situations with large numbers of fact/instances or partial matches.
• 64-bit Integers – Integers in CLIPS are now represented using the “long long” C data type
which provides a minimum of 64 bits of precision.
• Reset after Clear – A reset command is now performed after a clear command (which
includes the clear command issued internally by CLIPS when it is started). Since no user
constructs will be present after a clear, the primary effect of this behavior is to create the
initial-fact and initial-object.
• Pattern Addition – The initial-fact and initial-object patterns are no longer used in
triggering rules. When printing partial matches, the * symbol is used to indicate a not or
exists pattern that is satisfied.
• Module Specifiers – A module specifier can be used in expressions to reference a
deffunction or defgeneric that is exported by a module, but not specifically imported by the
module which is referencing it. For example: (UTIL::my-function a 3).
• Instance Name and Class Visibility – Instance names now have global scope and must be
unique regardless of their module. Instances of classes that are not in scope can be created if
the module name is specified as part of the class name. Messages can be sent to instances
regardless of whether the instance class is in scope.
• Command Prompt – Local variables bound at the command prompt using the bind
function persist until a reset or clear command is issued (see section 2.1.1).
• Printout Function – The deprecated use of the symbol t as a substitute for the crlf symbol
is no longer allowed.
• MicroEMACS Editor – The built-in editor is no longer supported.
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• New Functions and Commands - Several new functions and commands have been added.
They are:
• foreach (see section 12.6.10)
• operating-system (see section 12.7.12)
• Command and Function Changes - The following commands and functions have been
enhanced:
• matches (see section 13.6.4). This command now has a return value indicating the number
of matches, partial matches, and activations. The amount of output can be controlled with a
verbosity argument.
• open (see section 12.4.2.1). The r+ mode is no longer supported. New modes ab and rb have
been added.
• Help Functions – The help and help-path funtions are no longer supported
• Behavior Changes - The following changes have been made to behavior:
• A defgeneric redefinition warning is no longer printed when a defmethod is defined.
B.2 Version 6.24
• Allowed Classes Constraint Attribute – The allowed-classes constraint attribute allows a
slot containing an instance value to be restricted to the specified list of classes.
• New Functions and Commands - Several new functions and commands have been added.
They are:
• deftemplate-slot-allowed-values
• deftemplate-slot-cardinality
• deftemplate-slot-defaultp
• deftemplate-slot-default-value
• deftemplate-slot-existp
• deftemplate-slot-multip
• deftemplate-slot-names
• deftemplate-slot-range
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• deftemplate-slot-singlep
• deftemplate-slot-type
• get-char
• get-region
• ppfact
• read-number
• set-locale
• slot-allowed-classes
• Command and Function Changes - The following commands and functions have been
enhanced:
• format The formatting of printed numbers can be changed to use a native locale with the
set-locale function. The documentation has been updated to include the effect of the
precision argument on the d, g, o, and x format flags.
• Behavior Changes - The following changes have been made to behavior:
• The message displayed when a construct is redefined and compilations are being
watched is now more prominent.
• Bug Fixes - The following bugs were fixed by the 6.24 release:
• The DescribeClass macros were incorrectly defined.
• The sort function leaks memory when called with a multifield value of length zero.
• Link error occurred for the SlotExistError function when OBJECT_SYSTEM is set to 0
in setup.h.
• An error when calling the Eval function causes a subsequent call to
DeallocateEnvironmentData to fail.
• Loading a binary instance file from a run-time program caused a bus error.
• Incorrect activations could occur with the exists CE.
• Compilation errors occurred when compiling CLIPS source as C++ files.
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Appendix B: Update Release Notes
• The AssignFactSlotDefaults function did not correctly handle defaults for multifield
slots.
• The slot-default-value function crashed when no default existed for a slot (the ?NONE
value was specified).
• CLIPS crashed on AMD64 processor in the function used to generate hash values for
integers.
• A syntax error was not generated for the last deffunction or defmethod in a file if it was
missing the final closing right parenthesis.
• Compiler Support - The following compilers are now supported. See the Interfaces Guide
for more details.
• Metrowerks CodeWarrior 9.6 for Mac OS X.
• Xcode 2.3 for Mac OS X.
• Microsoft Visual C++ .NET 2003 for Windows.
B.3 Version 6.23
• Fact-Set Query Functions – Six new functions similar to the instance set query functions
have been added for determining and performing actions on sets of facts that satisfy
user-defined queries: any-factp, find-fact, find-all-facts, do-for-fact, do-for-all-facts, and
delayed-do-for-all-facts. The GetNextFactInTemplate function allows iteration from C over
the facts belonging to a specific deftemplate.
• Bug Fixes - The following bugs were fixed by the 6.23 release:
• Passing the wrong number of arguments to a deffunction through the funcall function
could cause unpredictable behavior including memory corruption.
• A large file name (at least 60 characters) passed into the fetch command causes a buffer
overrun.
• A large file name (at least 60 characters) passed into the constructs-to-c command
causes a buffer overrun.
• A large defclass or defgeneric name (at least 500 characters) causes a buffer overrun
when the profile-info command is called.
• A large module or construct name (at least 500 characters) causes a buffer overrun when
the get-<construct>-list command is called.
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• The FalseSymbol and TrueSymbol constants were not defined as described in the
Advanced Programming Guide. These constants have have now been defined as macros
so that their corresponding environment companion functions (EnvFalseSymbol and
EnvTrueSymbol) could be defined. See the Advanced Programming Guide for more
details.
• The slot-writablep function returns TRUE for slots having initialize-only access.
• Files created by the constructs-to-c function for use in a run-time program generate
compilation errors.
• Command and Function Changes - The following commands and functions have been
enhanced:
• funcall Multifield arguments are no longer expanded into multiple arguments before
being passed to the target function of the funcall. The expand$ function can be placed
around an argument to revert to the old behavior.
• Compiler Support - The following compilers are now supported. See the Interfaces Guide
for more details.
• Metrowerks CodeWarrior 9.4 for Mac OS X and Windows.
• Xcode 1.2 for Mac OS X.
B.4 Version 6.22
• Bug Fixes - The following bugs were fixed by the 6.22 release:
• Numerous fixes for functions and macros that did not accept the correct number of
arguments as specified in the Advanced Programming Guide. The following functions
and macros were corrected: Agenda, BatchStar, EnvGetActivationSalience,
EnvBatchStar, EnvFactDeftemplate, EnvFactExistp, EnvFactList, EnvFactSlotNames,
EnvGetNextInstanceInClassAndSubclasses, EnvLoadInstancesFromString,
EnvRestoreInstancesFromString, EnvSetOutOfMemoryFunction, FactDeftemplate,
FactExistp, FactList, FactSlotNames, GetNextInstanceInClassAndSubclasses,
LoadInstancesFromString, RestoreInstancesFromString, SetOutOfMemoryFunction.
B.5 Version 6.21
• Bug Fixes - The following bugs were fixed by the 6.21 release:
• The C GetDefglobalValue macro did not have the correct number of arguments.
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Appendix B: Update Release Notes
• The C RtnArgCount macro did not have the correct number of arguments.
• Erroneous error generated for object pattern under some circumstances.
• The C Save macro did not have the correct number of arguments.
• The C Eval and Build functions did not have the correct number of arguments.
• The progn$ index variable did not always return the correct value.
• The member$ function did not always return the correct value.
• C++ style comments in the code caused errors when using strict ANSI C compilation.
• The C LoadFactsFromString function did not have the correct number of arguments.
• Prior bug fix to the PutFactSlot C function prevented memory associated with the fact to
be garbage collected after the fact had been retracted. The original bug is now fixed
through a new API which allows embedded programs to temporarily disable garbage
collection. See section 1.4 of The Advanced Programming Guide for more details.
B.6 Version 6.2
• Environments – It is now possible in an embedded application to create multiple
environments into which programs can be loaded. See section 9 of The Advanced
Programming Guide for more details
• New Microsoft Windows and MacOS X Interfaces – An improved Windows 95/98/NT
CLIPS interface is now available for PC compatible computers. See section 2 of The
Interfaces Guide for more details. An improved MacOS X/9.0 CLIPS interface is now
available for Macintosh computers. See section 3 of The Interfaces Guide for more details.
• COOL Default Behavior – For the purpose of role inheritance, system defined classes
behave as concrete classes. The default value for the create-accessor facet is now read-
write. For the purpose of pattern-match inheritance, system defined classes behave as
reactive classes unless the inheriting class is abstract. This behavior can be restored to
CLIPS 6.1 behavior using the set-class-defaults-mode function.
• COOL Changes - The following changes have been made to instance behavior:
• Newly created instances are sent a create message.
• New Functions and Commands - Several new functions and commands have been added.
They are:
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• funcall
• get-class-defaults-mode
• set-class-defaults-mode
• string-to-field
• timer
• Command and Function Enhancements - The following commands and functions have
been enhanced:
• switch The requirement of having at least two case statements has been removed.
• printout The logical name nil now has special significance.
• sort Multifield as well as single-field values can now be sorted.
• random The integer value returned by the function can now be restricted to a specified
range of values.
• do-for-instance Multiple actions can be specified in the action portion of the query
(which previously required an explicit progn call).
• do-for-all-instances Multiple actions can be specified in the action portion of the query
(which previously required an explicit progn call).
• delayed-do-for-all-instances Multiple actions can be specified in the action portion of
the query (which previously required an explicit progn call).
• Bug Fixes - The following bugs were fixed by the 6.20 release:
• Inner member variables in nested instance set queries could be confused with member
variables from an outer query. This would happen if the inner member variable name
shared all of its characters with the first N characters of the outer variable name.
• Some data structures generated by object pattern matching were not garbage collected
until a run command was issued.
• Backspaces were not properly handled in the display window of the Windows interface.
• The module name was not specified for deffunctions by the save command.
• Garbage collection triggered by evaluating the arguments to str-cat/sym-cat could
change the value of the arguments already retrieved.
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Appendix B: Update Release Notes
• The PutFactSlot C function does not properly increment/decrement the slot value that it
changes.
• Defrule data structures could end up in an invalid state during a retract if a fact/object
matched two patterns in a rule and one pattern was inside two nested not conditional
elements and the other pattern was inside one not conditional element.
• The implode$ function does not properly handle the \ character in a string.
• Garbage collection triggered by expression evaluation during an assert-string call could
corrupt the fact being asserted.
• Inappropriate fact syntax for the assert-string function causes a crash.
• The evaluation error flag was not reset before calling the AssertString C function.
• The FindDefclass C function crashes when the specified module is not defined.
• The save command did not always properly save constructs when modules using
import/export specifications were used.
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Appendix C:
Glossary
This section defines some of the terminology used throughout this manual.
abstraction
The definition of new classes to describe the common properties
and behavior of a group of objects.
action
A function executed by a construct (such as the RHS of a rule)
which typically has no return value, but performs some useful
action (such as the printout action) (see section 12).
activation
A rule is activated if all of its conditional elements are satisfied
and it has not yet fired based on a specific set of matching pattern
entities that caused it to be activated. Note that a rule can be
activated by more than one set of pattern entities. An activated
rule that is placed on the agenda is called an activation.
active instance
The object responding to a message which can be referred to by
?self in the message’s handlers.
agenda
A list of all rules that are presently ready to fire. It is sorted by
salience values and the current conflict resolution strategy. The
rule at the top of the agenda is the next rule that will fire.
antecedent
The LHS of a rule.
bind
The action of storing a value in a variable.
class
Template for describing the common properties (slots) and
behavior (message-handlers) of a group of objects called instances
of the class.
class precedence list
A linear ordering of classes which describes the path of
inheritance for a class.
command
A function executed at the top-level command prompt (such as the
reset command) typically having no return value.
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Appendix C: Glossary
command prompt
In the interactive interface, the “CLIPS>” prompt which indicates
that CLIPS is ready for a command to be entered.
condition
A conditional element.
conditional
element
A restriction on the LHS of a rule which must be satisfied in order
for the rule to be applicable (also referred to as a CE).
conflict resolution
strategy
A method for determining the order in which rules should fire
among rules with the same salience. There are seven different
conflict resolution strategies: depth, breadth, simplicity,
complexity, lex, mea, and random.
consequent
The RHS of a rule.
constant
A non-varying single field value directly expressed as a series of
characters.
constraint
In patterns, a constraint is a requirement that is placed on the value
of a field from a fact or instance that must be satisified in order for
the pattern to be satisfied. For example, the ~red constraint is
satisfied if the field to which the constraint is applied is not the
symbol red. The term constraint is also used to refer to the legal
values allowed in the slots of facts and instances.
construct
A high level CLIPS abstraction used to add components to the
knowledge base.
current focus
The module from which activations are selected to be fired.
current module
The module to which newly defined constructs that do not have a
module specifier are added. Also is the default module for certain
commands which accept as an optional argument a module name
(such as list-defrules).
daemon
A message-handler which executes implicitly whenever some
action is taken upon an object, such as initialization, deletion, or
slot access.
deffunction
A non-overloaded function written directly in CLIPS.
deftemplate fact
A deftemplate name followed by a list of named fields (slots) and
specific values used to represent a deftemplate object. Note that a
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deftemplate fact has no inheritance. Also called a non-ordered
fact.
deftemplate object
An informal term for the entity described by a deftemplate. A
deftemplate object is simply an informal term for the collections
of slots (without specific values) which define a deftemplate.
Deftemplate objects do not have inheritance
deftemplate pattern
A list of named constraints (constrained slots). A deftemplate
pattern describes the attributes and associated values of a
deftemplate object. Also called a non-ordered pattern.
delimiter
A character which indicates the end of a symbol. The following
characters act as delimiters: any non-printable ASCII character
(including spaces, tabs, carriage returns, and line feeds), a double
quote, opening and closing parenthesis “(” and “)”, an ampersand
“&”, a vertical bar “|”, a less than “<”, a semicolon “;”, and a tilde
“~”.
dynamic binding
The deferral of which message-handlers will be called for a
message until run-time.
encapsulation
The requirement that all manipulation of instances of user-defined
classes be done with messages.
expression
A function call with arguments specified.
external-address
The address of an external data structure returned by a function
(written in a language such as C or Ada) that has been integrated
with CLIPS (see section 2.3.1 for more details).
external function
A function written in an external language (such as C or Ada)
defined by the user or provided by CLIPS and called from within
CLIPS rules.
facet
A component of a slot specification for a class, e.g. default value
and cardinality.
fact
An ordered or deftemplate (non-ordered) fact. Facts are the data
about which rules reason and represent the current state of the
world.
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Appendix C: Glossary
fact-address
A pointer to a fact obtained by binding a variable to the fact which
matches a pattern on the LHS of a rule.
fact-identifier
A shorthand notation for referring to a fact. It consists of the
character “f”, followed by a dash, followed by the fact-index of
the fact.
fact-index
A unique integer index used to identify a particular fact.
fact-list
The list of current facts.
field
A placeholder (named or unnamed) that has a value.
fire
A rule is said to have fired if all of its conditions are satisfied and
the actions then are executed.
float
A number that begins with an optional sign followed optionally in
order by zero or more digits, a decimal point, zero or more digits,
and an exponent (consisting of an e or E followed by an integer).
A floating point number must have at least one digit in it (not
including the exponent) and must either contain a decimal point or
an exponent (see section 2.3.1 for more details).
focus
As a verb, refers to changing the current focus. As a noun, refers
to the current focus.
focus stack
The list of modules that have been focused upon. The module at
the top of the focus stack is the current focus. When all the
activations from the current focus have been fired, the current
focus is removed from the focus stack and the next module on the
stack becomes the current focus.
function
A piece of executable code identified by a specific name which
returns a useful value or performs a useful side effect. Typically
only used to refer to functions which do return a value (whereas
commands and actions are used to refer to functions which do not
return a value).
generic dispatch
The process whereby applicable methods are selected and
executed for a particular generic function call.
generic function
A function written in CLIPS which can do different things
depending on what the number and types of its arguments.
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inference engine
The mechanism provided by CLIPS which automatically matches
patterns against the current state of the fact-list and list of
instances and determines which rules are applicable.
inheritance
The process whereby one class can be defined in terms of other
class(es).
instance
An object is an instance of a class. Throughout the documentation,
the term instance usually refers to objects which are instances of
user-defined classes.
instance (of a
user-defined class)
An object which can only be manipulated via messages, i.e all
objects except symbols, strings, integers, floats, multifields and
external-addresses.
instance-address
The address of an instance of a user-defined class (see section
2.3.1 for more details).
instance-name
A symbol enclosed within left and right brackets (see section 2.3.1
for more details). An instance-name refers to an object of the
specified name which is an instance of a user-defined class.
instance-set
An ordered collection of instances of user-defined classes. Each
member of an instance-set is an instance of a set of classes, where
the set can be different for each member.
instance-set distributed
action
A user-defined expression which is evaluated for every
instance-set which satisfies an instance-set query.
instance-set query
A user-defined boolean expression applied to an instance-set to
see if it satisfies further user-defined criteria.
integer
A number that begins with an optional sign followed by one or
more digits (see section 2.3.1 for more details).
LHS
Left-Hand Side. The set of conditional elements that must be
satisfied for the actions of the RHS of a rule to be performed.
list
A group of items with no implied order.
logical name
A symbolic name that is associated with an I/O source or
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Appendix C: Glossary
destination.
message
The mechanism used to manipulate an object.
message dispatch
The process whereby applicable message-handlers are selected
and executed for a particular message.
message-handler
An implementation of a message for a particular class of objects.
message-handler
precedence
The property used by the message dispatch to select between
handlers when more than one is applicable to a particular message.
method
An implementation of a generic function for a particular set of
argument restrictions.
method index
A shorthand notation for referring to a method with a particular set
of parameter restrictions.
method precedence
The property used by the generic dispatch to select a method when
more than one is applicable to a particular generic function call.
module
A workspace where a set of constructs can be grouped together
such that explicit control can be maintained over restricting the
access of the constructs by other modules. Also used to control the
flow of execution of rules through the use of the focus command.
module specifier
A notation for specifying a module. It consists of a module name
followed by two colons. When placed before a construct name,
it’s used to specify which module a newly defined construct is to
be added to or to specify which construct a command will affect if
that construct is not in the current module.
multifield
A sequence of unnamed placeholders each having a value.
multifield value
A sequence of zero or more single-field values.
non-ordered fact
A deftemplate fact.
number
An integer or float.
object
A symbol, a string, a floating-point or integer number, a multifield
value, an external address or an instance of a user-defined class.
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order
Position is significant.
ordered fact
A sequence of unnamed fields.
ordered pattern
A sequence of constraints.
overload
The process whereby a generic function can do different things
depending on the types and number of its arguments, i.e. the
generic function has multiple methods.
pattern
A conditional element on the LHS of a rule which is used to match
facts in the fact-list.
pattern entity
An item that is capable of matching a pattern on the LHS of a rule.
Facts and instances are the only types of pattern entities available.
pattern-matching
The process of matching facts or instances to patterns on the LHS
of rules.
polymorphism
The ability of different objects to respond to the same message in
a specialized manner.
primitive type object
A symbol, string, integer, float, multifield or external-address.
relation
The first field in a fact or fact pattern. Synonomous with the
associated deftemplate name.
RHS
Right-Hand Side. The actions to be performed when the LHS of a
rule is satisfied.
rule
A collection of conditions and actions. When all patterns are
satisfied, the actions will be taken.
salience
A priority number given to a rule. When multiple rules are ready
for firing, they are fired in order of priority. The default salience is
zero (0). Rules with the same salience are fired according to the
current conflict resolution strategy.
sequence
An ordered list.
shadowed
message-handler
A message-handler that must be explicitly called by another
message-handler in order to execute.
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Appendix C: Glossary
shadowed method
A method that must be explicitly called by another method in
order to execute.
single-field value
One of the primitive data types: float, integer, symbol, string,
external-address, instance-name, or instance-address.
slot
Named single-field or multifield. To write a slot give the field
name (attribute) followed by the field value. A single-field slot has
one value, while a multifield slot has zero or more values. Note
that a multifield slot with one value is strictly not the same as a
single field slot. However, the value of a single-field slot (or
variable) may match a multifield slot (or multifield variable) that
has one field.
slot-accessor
Implicit message-handlers which provide read and write access to
slots of an object.
specificity (class)
A class that precedes another class in a class precedence list is
said to be more specific. A class is more specific than any of its
superclasses.
specificity (rule)
A measure of how “specific” the LHS of a rule is in the
pattern-matching process. The specificity is determined by the
number of constants, variables, and function calls used within
LHS conditional elements.
string
A set of characters that starts with double quotes (") and is
followed by zero or more printable characters and ends with
double quotes (see section 2.3.1 for more details).
subclass
If a class inherits from a second class, the first class is a subclass
of the second class.
superclass
If a class inherits from a second class, the second class is a
superclass of the first class.
symbol
Any sequence of characters that starts with any printable ASCII
character and is followed by zero or more characters (see section
2.3.1 for more details).
top level
In the interactive interface, the “CLIPS>” prompt which indicates
that CLIPS is ready for a command to be entered.
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value
A single or multifield value.
variable
An symbolic location which can store a value.
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Appendix D:
Performance Considerations
This appendix explains various techniques that the user can apply to a CLIPS program to
maximize performance. Included are discussions of pattern ordering in rules, use of deffunctions
in lieu of non-overloaded generic functions, parameter restriction ordering in generic function
methods, and various approaches to improving the speed of message-passing and reading slots of
instances.
D.1 Ordering of Patterns on the LHS
The issues which affect performance of a rule-based system are considerably different from
those which affect conventional programs. This section discusses the single most important
issue: the ordering of patterns on the LHS of a rule.
CLIPS is a rule language based on the RETE algorithm. The RETE algorithm was designed
specifically to provide very efficient pattern-matching. CLIPS has attempted to implement this
algorithm in a manner that combines efficient performance with powerful features. When used
properly, CLIPS can provide very reasonable performance, even on microcomputers. However,
to use CLIPS properly requires some understanding of how the pattern-matcher works.
Prior to initiating execution, each rule is loaded into the system and a network of all patterns that
appear on the LHS of any rule is constructed. As facts and instances of reactive classes (referred
to collectively as pattern entities) are created, they are filtered through the pattern network. If the
pattern entities match any of the patterns in the network, the rules associated with those patterns
are partially instantiated. When pattern entities exist that match all patterns on the LHS of the
rule, variable bindings (if any) are considered. They are considered from the top to the bottom;
i.e., the first pattern on the LHS of a rule is considered, then the second, and so on. If the variable
bindings for all patterns are consistent with the constraints applied to the variables, the rules are
activated and placed on the agenda.
This is a very simple description of what occurs in CLIPS, but it gives the basic idea. A number
of important considerations come out of this. Basic pattern-matching is done by filtering through
the pattern network. The time involved in doing this is fairly constant. The slow portion of basic
pattern-matching comes from comparing variable bindings across patterns. Therefore, the single
most important performance factor is the ordering of patterns on the LHS of the rule.
Unfortunately, there are no hard and fast methods that will always order the patterns properly. At
best, there seem to be three “quasi” methods for ordering the patterns.
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Appendix D: Performance Considerations
1) Most specific to most general. The more wildcards or unbound variables there are in a
pattern, the lower it should go. If the rule firing can be controlled by a single pattern, place
that pattern first. This technique often is used to provide control structure in an expert
system; e.g., some kind of “phase” fact. Putting this kind of pattern first will guarantee that
the rest of the rule will not be considered until that pattern exists. This is most effective if
the single pattern consists only of literal constraints. If multiple patterns with variable
bindings control rule firing, arrange the patterns so the most important variables are bound
first and compared as soon as possible to the other pattern constraints. The use of phase facts
is not recommended for large programs if they are used solely for controlling the flow of
execution (use modules instead).
2) Patterns with the lowest number of occurrences in the fact-list or instance-list should go near
the top. A large number of patterns of a particular form in the fact-list or instance-list can
cause numerous partial instantiations of a rule that have to be “weeded” out by comparing
the variable bindings, a slower operation.
3) Volatile patterns (ones that are retracted and asserted continuously) should go last,
particularly if the rest of the patterns are mostly independent. Every time a pattern entity is
created, it must be filtered through the network. If a pattern entity causes a partial rule
instantiation, the variable bindings must be considered. By putting volatile patterns last, the
variable bindings only will be checked if all of the rest of the patterns already exist.
These rules are not independent and commonly conflict with each other. At best, they provide
some rough guidelines. Since all systems have these characteristics in different proportions, at a
glance the most efficient manner of ordering patterns for a given system is not evident. The best
approach is to develop the rules with minimal consideration of ordering. When the reasoning is
fairly well verified, experiment with the patterns until the optimum configuration is found.
Another performance issue is the use of multifield variables and wildcards ($?). Although they
provide a powerful capability, they must be used very carefully. Since they can bind to zero or
more fields, they can cause multiple instantiations of a single rule. In particular, the use of
multiple multifield variables in one pattern can cause a very large number of instantiations.
Some final notes on rule performance. Experience suggests that the user should keep the expert
system “lean and mean.” The list of pattern entities should not be used as a data base for storage
of extraneous information. Store and pattern-match only on that information necessary for
reasoning. Keep the pattern-matching to a minimum and be as specific as possible. Many short,
simple rules perform better than long, complex rules and have the added benefit of being easier
to understand and maintain.
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D.2 Deffunctions versus Generic Functions
Deffunctions execute more quickly than generic function because generic functions must first
examine their arguments to determine which methods are applicable. If a generic function has
only one method, a deffunction probably would be better. Care should be taken when
determining if a particular function truly needs to be overloaded. In addition, if recompiling and
relinking CLIPS is not prohibitive, user-defined external functions are even more efficient than
deffunctions. This is because deffunction are interpreted whereas external functions are directly
executed. For more details, see sections 7 and 8.2.
D.3 Ordering of Method Parameter Restrictions
When the generic dispatch examines a generic function’s method to determine if it is applicable
to a particular set of arguments, it examines that method’s parameter restrictions from left to
right. The programmer can take advantage of this by placing parameter restrictions which are
less frequently satisfied than others first in the list. Thus, the generic dispatch can conclude as
quickly as possible when a method is not applicable to a generic function call. If a group of
restrictions are all equally likely to be satisfied, placing the simpler restrictions first, such as
those without queries, will also allow the generic dispatch to conclude more quickly for a method
that is not applicable. For more details, see section 8.4.3.
D.4 Instance-Addresses versus Instance-Names
COOL allows instances of user-defined classes to be referenced either by address or by name in
functions which manipulate instances, such as message-passing with the send function.
However, when an instance is referenced by name, CLIPS must perform an internal lookup to
find the instance-address anyway. If the same instance is going to be manipulated many times, it
might be advantageous to store the instance-address and use that as a reference. This will allow
CLIPS to always go directly to the instance. For more details, see sections 2.4.2 and 12.16.4.6.
D.5 Reading Instance Slots Directly
Normally, message-passing must be used to read or set a slot of an instance. However, slots can
be read directly within instance-set queries and message-handlers, and they can be set directly
within message-handlers. Accessing slots directly is significantly faster than message-passing.
Unless message-passing is required (because of slot daemons), direct access should be used
when allowed. For more details, see sections 9.4.2, 9.4.3, 9.4.4, 9.6.3, 9.6.4 and 9.7.3.
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Appendix E:
CLIPS Warning Messages
CLIPS typically will display two kinds of warning messages: those associated with executing
constructs and those associated with loading constructs. This appendix describes some of the
more common warning messages and what they mean. Each message begins with a unique
identifier enclosed in brackets followed by the keyword WARNING; the messages are listed
here in alphabetic order according to the identifier.
[CONSCOMP1] WARNING: Base file name exceeds 3 characters.
This may cause files to be overwritten if file name length
is limited on your platform.
The constructs-to-c command generates file names using the file name prefix supplied as an
argument. If this base file name is longer than three characters, then the possibility exists that
files may be overwritten if file name length is limited on your platform.
[CONSCOMP2] WARNING: Array name <arrayName> exceeds 6 characters in length.
This variable may be indistinguishable from another by the linker.
The constructs-to-c command generates arrays for storing data structures. If the
SHORT_LINK_NAMES compiler flag is enabled, then this warning message is displayed if
generated array names exceed six characters in length.
[CSTRCPSR1] WARNING: Redefining <constructType>: <constructName>
This indicates that a previously defined construct of the specified type has been redefined.
[CSTRNBIN1] WARNING: Constraints are not saved with a binary image when dynamic
constraint checking is disabled
or
[CSTRNCMP1] WARNING: Constraints are not saved with a constructs-to-c image when
dynamic constraint checking is disabled
These warnings occur when dynamic constraint checking is disabled and the constructs-to-c or
bsave commands are executed. Constraints attached to deftemplate and defclass slots will not be
saved with the runtime or binary image in these cases since it is assumed that dynamic constraint
checking is not required. Enable dynamic constraint checking with the
set-dynamic-constraint-checking function before calling constructs-to-c or bsave in order to
include constraints in the runtime or binary image.
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Appendix E: CLIPS Warning Messages
[DFFNXFUN1] WARNING: Deffunction <name> only partially deleted due to usage by
other constructs.
During a clear or deletion of all deffunctions, only the actions of a deffunction were deleted
because another construct which also could not be deleted referenced the deffunction.
Example:
CLIPS>
(deffunction foo ()
(printout t "Hi there!" crlf))
CLIPS>
(deffunction bar ()
(foo)
(undeffunction *))
CLIPS> (bar)
[GENRCBIN1] WARNING: COOL not installed! User-defined class in method restriction
substituted with OBJECT.
This warning occurs when a generic function method restricted by defclasses is loaded using the
bload command into a CLIPS configuration where the object language is not enabled. The
restriction containing the defclass will match any of the primitive types.
[OBJBIN1] WARNING: Around message-handlers are not supported in this environment.
This warning occurs when an around message-handler is loaded using the bload command into
a CLIPS configuration not supporting imperative message-handlers.
[OBJBIN2] WARNING: Before and after message-handlers are not supported in this
environment.
This warning occurs when a before or an after message-handler is loaded using the bload
command into a CLIPS configuration not supporting auxiliary message-handlers.
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Appendix F:
CLIPS Error Messages
CLIPS typically will display two kinds of error messages: those associated with executing
constructs and those associated with loading constructs. This appendix describes some of the
more common error messages and what they mean. Each message begins with a unique identifier
enclosed in brackets; the messages are listed here in alphabetic order according to the identifier.
[AGENDA1] Salience value must be an integer value.
Salience requires a integer argument and will otherwise result in this error message.
Example:
CLIPS> (defrule error (declare (salience a)) =>)
[AGENDA2] Salience value out of range <min> to <max>
The range of allowed salience has an explicit limit; this error message will result if the value is
out of that range.
Example:
CLIPS> (defrule error (declare (salience 20000)) =>)
[AGENDA3] This error occurred while evaluating the salience [for rule <name>]
When an error results from evaluating a salience value for a rule, this error message is given.
[ANALYSIS1] Duplicate pattern-address <variable name> found in CE <CE number>.
This message occurs when two facts or instances are bound to the same pattern-address variable.
Example:
CLIPS> (defrule error ?f <- (a) ?f <- (b) =>)
[ANALYSIS2] Pattern-address <variable name> used in CE #2 was previously bound
within a pattern CE.
A variable first bound within a pattern cannot be later bound to a fact-address.
Example:
CLIPS> (defrule error (a ?f) ?f <- (b) =>)
[ANALYSIS3] Variable <variable name> is used as both a single and multifield variable.
Variables on the LHS of a rule cannot be bound to both single and multifield variables.
Example:
CLIPS> (defrule error (a ?x $?x) =>)
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Appendix F: CLIPS Error Messages
[ANALYSIS4] Variable <variable name> [found in the expression <expression>]
was referenced in CE <CE number> <field or slot identifier> before being defined
A variable cannot be referenced before it is defined and, thus, results in this error message.
Example:
CLIPS> (defrule foo (a ~?x) =>)
[ARGACCES1] Function <name> expected at least <minimum> and no more than
<maximum> argument(s)
This error occurs when a function receives less than the minimum number or more than the
maximum number of argument(s) expected.
[ARGACCES2] Function <function-name> was unable to open file <file-name>
This error occurs when the specified function cannot open a file.
[ARGACCES3] Function <name1> received a request from function <name2> for
argument #<number> which is non-existent
This error occurs when a function is passed fewer arguments than were expected.
[ARGACCES4] Function <name> expected exactly <number> argument(s)
This error occurs when a function that expects a precise number of argument(s) receives an
incorrect number of arguments.
[ARGACCES4] Function <name> expected at least <number> argument(s)
This error occurs when a function does not receive the minimum number of argument(s) that it
expected.
[ARGACCES4] Function <name> expected no more than <number> argument(s)
This error occurs when a function receives more than the maximum number of argument(s)
expected.
[ARGACCES5] Function <name> expected argument #<number> to be of type
<data-type>
This error occurs when a function is passed the wrong type of argument.
[ARGACCES6] Function <name1> received a request from function <name2> for
argument #<number> which is not of type <data-type>
This error occurs when a function requests from another function the wrong type of argument,
typically a string or symbol, when expecting a number or vice versa.
[BLOAD1] Cannot load <construct type> construct with binary load in effect.
If the bload command was used to load in a binary image, then the named construct cannot be
entered until a clear command has been performed to remove the binary image.
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[BLOAD2] File <file-name> is not a binary construct file
This error occurs when the bload command is used to load a file that was not created with the
bsave command.
[BLOAD3] File <file-name> is an incompatible binary construct file
This error occurs when the bload command is used to load a file that was created with the bsave
command using a different version of CLIPS.
[BLOAD4] The CLIPS environment could not be cleared.
Binary load cannot continue.
A binary load cannot be performed unless the current CLIPS environment can be cleared.
[BLOAD5] Some constructs are still in use by the current binary image:
<construct-name 1>
<construct-name 2>
...
<construct-name N>
Binary <operation> cannot continue.
This error occurs when the current binary image cannot be cleared because some constructs are
still being used. The <operation> in progress may either be a binary load or a binary clear.
[BLOAD6] The following undefined functions are referenced by this binary image:
<function-name 1>
<function-name 2>
...
<function-name N>
This error occurs when a binary image is loaded that calls functions which were available in the
CLIPS executable that originally created the binary image, but which are not available in the
CLIPS executable that is loading the binary image.
[BSAVE1] Cannot perform a binary save while a binary load is in effect.
The bsave command does not work when a binary image is loaded.
[CLASSEXM1] Inherited slot <slot-name> from class <slot-name> is not valid for function
slot-publicp
This error message occurs when the function slot-publicp is given an inherited slot. This
function can only be used on slots defined in the given class.
Example:
CLIPS>
(defclass FOO (is-a USER)
(slot woz (visibility private)))
CLIPS>
(defclass BAR (is-a FOO))
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Appendix F: CLIPS Error Messages
CLIPS> (slot-publicp BAR woz)
[CLASSFUN1] Unable to find class <class name> in function <function name>.
This error message occurs when a function is given a non-existent class name.
Example:
CLIPS> (class-slots FOO)
[CLASSFUN2] Maximum number of simultaneous class hierarchy traversals exceeded
<number>.
This error is usually caused by too many simultaneously active instance-set queries, e.g.,
do-for-all-instances. The direct or indirect nesting of instance-set query functions is limited in
the following way:
Ci is the number of members in an instance-set for the ith nested instance-set query function.
N is the number of nested instance-set query functions.
<= 128 (the default upper limit)
Example:
CLIPS>
(deffunction my-func ()
(do-for-instance ((?a USER) (?b USER) (?c USER)) TRUE
(printout t ?a " " ?b " " ?c crlf))
; The sum here is C1 = 3 which is OK.
CLIPS>
(do-for-all-instances ((?a OBJECT) (?b OBJECT)) TRUE
(my-func))
; The sum here is C1 + C2 = 2 + 3 = 5 which is OK.
The default upper limit of 128 should be sufficient for most if not all applications. However, the
limit may be increased by editing the header file OBJECT.H and recompiling CLIPS.
[CLASSPSR1] An abstract class cannot be reactive.
Only concrete classes can be reactive.
Example:
CLIPS>
(defclass FOO (is-a USER)
(role abstract)
(pattern-match reactive))
∑
i=1
N
Ci
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[CLASSPSR2] Cannot redefine a predefined system class.
Predefined system classes cannot be modified by the user.
Example:
CLIPS> (defclass STRING (is-a NUMBER))
[CLASSPSR3] <name> class cannot be redefined while outstanding references to it still
exist.
This error occurs when an attempt to redefine a class is made under one or both of the following
two circumstances:
1) The class (or any of its subclasses) has instances.
2) The class (or any of its subclasses) appear in the parameter restrictions of any generic
function method.
Before the class can be redefined, all such instances and methods must be deleted.
Example:
CLIPS> (defclass A (is-a USER))
CLIPS> (defmethod foo ((?a A LEXEME)))
CLIPS> (defclass A (is-a OBJECT)))
[CLASSPSR4] Class <attribute> already declared.
Only one specification of a class attribute is allowed.
Example:
CLIPS>
(defclass A (is-a USER)
(role abstract)
(role concrete))
[CLSLTPSR1] Duplicate slots not allowed.
Slots in a defclass must be unique.
Example:
CLIPS>
(defclass A (is-a USER)
(slot foo)
(slot foo))
[CLSLTPSR2] <name> facet already specified.
Only one occurrence of a facet per slot is allowed.
Example:
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Appendix F: CLIPS Error Messages
CLIPS>
(defclass A (is-a USER)
(slot foo (access read-only)
(access read-write)))
[CLSLTPSR3] Cardinality facet can only be used with multifield slots
Single-field slots by definition have a cardinality of one.
Example:
CLIPS>
(defclass A (is-a USER)
(slot foo (cardinality 3 5)))
[CLSLTPSR4] read-only slots must have a default value
Since slots cannot be unbound and read-only slots cannot be set after initial creation of the
instance, read-only slots must have a default value.
Example:
CLIPS>
(defclass A (is-a USER)
(slot foo (access read-only)
(default ?NONE)))
[CLSLTPSR5] read-only slots cannot have a write accessor
Since read-only slots cannot be changed after initializationof the instance, a write accessor
(put- message-handler) is not allowed.
Example:
CLIPS>
(defclass A (is-a USER)
(slot foo (access read-only)
(create-accessor write)))
[CLSLTPSR6] no-inherit slots cannot also be public
no-inherit slots are by definition not accessible to subclasses and thus only visible to the parent
class.
Example:
CLIPS>
(defclass A (is-a USER)
(slot foo (propagation no-inherit)
(visibility public)))
[COMMLINE1] Expected a '(', constant, or global variable
This message occurs when a top-level command does not begin with a '(', constant, or global
variable.
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Example:
CLIPS> )
[COMMLINE2] Expected a command.
This message occurs when a top-level command is not a symbol.
Example:
CLIPS> ("facts"
[CONSCOMP1] Invalid file name <fileName> contains '.'
A '.' cannot be used in the file name prefix that is passed to the constructs-to-c command since
this prefix is used to generate file names and some operating systems do not allow more than one
'.' to appear in a file name.
[CONSTRCT1] Some constructs are still in use. Clear cannot continue.
This error occurs when the clear command is issued when a construct is in use (such as a rule
that is firing).
[CSTRCPSR1] Expected the beginning of a construct.
This error occurs when the load command expects a left parenthesis followed a construct type
and these token types are not found.
[CSTRCPSR2] Missing name for <construct-type> construct
This error occurs when the name is missing for a construct that requires a name.
Example:
CLIPS> (defgeneric ())
[CSTRCPSR3] Cannot define <construct-type> <construct-name> because of an
import/export conflict.
or
[CSTRCPSR3] Cannot define defmodule <defmodule-name> because of an import/export
conflict cause by the <construct-type> <construct-name>.
A construct cannot be defined if defining the construct would allow two different definitions of
the same construct type and name to both be visible to any module.
Example:
CLIPS> (defmodule MAIN (export ?ALL))
CLIPS> (deftemplate MAIN::foo)
CLIPS> (defmodule BAR (import MAIN ?ALL))
CLIPS> (deftemplate BAR::foo (slot x))
[CSTRCPSR4] Cannot redefine <construct-type> <construct-name> while it is in use.
A construct cannot be redefined while it is being used by another construct or other data structure
(such as a fact or instance).
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Appendix F: CLIPS Error Messages
Example:
CLIPS> (clear)
CLIPS> (deftemplate bar)
CLIPS> (assert (bar))
<Fact-0>
CLIPS> (deftemplate (bar (slot x)))
[CSTRNCHK1] Message Varies
This error ID covers a range of messages indicating a type, value, range, or cardinality violation.
Example:
CLIPS> (deftemplate foo (slot x (type SYMBOL)))
CLIPS> (assert (foo (x 3)))
[CSTRNPSR1] The <first attribute name> attribute conflicts with the <second attribute
name> attribute.
This error message occurs when two slot attributes conflict.
Example:
CLIPS> (deftemplate foo (slot x (type SYMBOL) (range 0 2)))
[CSTRNPSR2] Minimum <attribute> value must be less than
or equal to the maximum <attribute> value.
The minimum attribute value for the range and cardinality attributes must be less than or equal to
the maximum attribute value for the attribute.
Example:
CLIPS> (deftemplate foo (slot x (range 8 1)))
[CSTRNPSR3] The <first attribute name> attribute cannot be used in conjunction with
the <second attribute name> attribute.
The use of some slot attributes excludes the use of other slot attributes.
Example:
CLIPS> (deftemplate foo (slot x (allowed-values a)
(allowed-symbols b)))
[CSTRNPSR4] Value does not match the expected type for the <attribute name> attribute.
The arguments to an attribute must match the type expected for that attribute (e.g. integers must
be used for the allowed-integers attribute).
Example:
CLIPS> (deftemplate example (slot x (allowed-integers 3.0)))
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[CSTRNPSR5] The cardinality attribute can only be used with multifield slots.
The cardinality attribute can only be used for slots defined with the multislot keyword.
Example:
CLIPS> (deftemplate foo (slot x (cardinality 1 1)))
[CSTRNPSR6] Minimum cardinality value must be greater than or equal to zero.
A multislot with no value has a cardinality of 0. It is not possible to have a lower cardinality.
Example:
CLIPS> (deftemplate foo (multislot x (cardinality -3 1)))
[DEFAULT1] The default value for a single field slot must be a single field value.
This error occurs when the default or default-dynamic attribute for a single-field slot does not
contain a single value or an expression returning a single value.
Example:
CLIPS> (deftemplate error (slot x (default)))
[DFFNXPSR1] Deffunctions are not allowed to replace constructs.
A deffunction cannot have the same name as any construct.
Example:
CLIPS> (deffunction defgeneric ())
[DFFNXPSR2] Deffunctions are not allowed to replace external functions.
A deffunction cannot have the same name as any system or user-defined external function.
Example:
CLIPS> (deffunction + ())
[DFFNXPSR3] Deffunctions are not allowed to replace generic functions.
A deffunction cannot have the same name as any generic function.
Example:
CLIPS> (defgeneric foo)
CLIPS> (deffunction foo ())
[DFFNXPSR4] Deffunction <name> may not be redefined while it is executing.
A deffunction can be loaded at any time except when a deffunction of the same name is already
executing.
Example:
CLIPS>
(deffunction foo ()
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Appendix F: CLIPS Error Messages
(build "(deffunction foo ())"))
CLIPS> (foo)
[DFFNXPSR5] Defgeneric <name> imported from module <module name> conflicts with
this deffunction.
A deffunction cannot have the same name as any generic function imported from another
module.
Example:
CLIPS> (defmodule MAIN (export ?ALL))
CLIPS> (defmethod foo ())
CLIPS> (defmodule FOO (import MAIN ?ALL))
CLIPS> (deffunction foo)
[DRIVE1] This error occurred in the join network
Problem resides in join #<pattern-number> in rule(s):
<problem-rules>+
This error pinpoints other evaluation errors associated with evaluating an expression within the
join network. The specific pattern of the problem rules is identified.
[EMATHFUN1] Domain error for <function-name> function
This error occurs when an argument passed to a math function is not in the domain of values for
which a return value exists.
[EMATHFUN2] Argument overflow for <function-name> function
This error occurs when an argument to an extended math function would cause a numeric
overflow.
[EMATHFUN3] Singularity at asymptote in <function-name> function
This error occurs when an argument to a trigonometric math function would cause a singularity.
[EVALUATN1] Variable <name> is unbound
This error occurs when a local variable not set by a previous call to bind is accessed at the top
level.
Example:
CLIPS> (progn ?error)
[EVALUATN2] No function, generic function or deffunction of name <name> exists for
external call.
IThis error occurs only when an invalid function name is passed to the external C
access routine CLIPSFunctionCall.
[EXPRNPSR1] A function name must be a symbol
In the following example, '~' is recognized by CLIPS as an operator, not a function:
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Example:
CLIPS> (+ (~ 3 4) 4)
[EXPRNPSR2] Expected a constant, variable, or expression
In the following example, '~' is an operator and is illegal as an argument to a function call:
Example:
CLIPS> (<= ~ 4)
[EXPRNPSR3] Missing function declaration for <name>
CLIPS does not recognize <name> as a declared function and gives this error message.
Example:
CLIPS> (xyz)
[EXPRNPSR4] $ Sequence operator not a valid argument for <name>.
The sequence expansion operator cannot be used with certain functions.
Example:
CLIPS> (set-sequence-operator-recognition TRUE)
FALSE
CLIPS> (defrule foo (x $?y) => (assert (x1 $?y)))
[FACTMCH1] This error occurred in the pattern network
Currently active fact: <newly assert fact>
Problem resides in slot <slot name>
Of pattern #<pattern-number> in rule(s):
<problem-rules>+
This error pinpoints other evaluation errors associated with evaluating an expression within the
pattern network. The specific pattern and field of the problem rules are identified.
[FACTMNGR1] Facts may not be retracted during pattern-matching
or
[FACTMNGR2] Facts may not be retracted during pattern-matching
Functions used on the LHS of a rule should not have side effects (such as the creation of a new
instance or fact).
Example:
CLIPS>
(defrule error
(test (assert (blah)))
=>)
CLIPS> (reset)
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[FACTRHS1] Template <name> does not exist for assert.
This error occurs when an assert is attempted for a deftemplate which does not exist in a runtime
or active bload image. In other situations, CLIPS will create an implied deftemplate if one does
not already exist.
Example:
CLIPS> (clear)
CLIPS> (bsave error.bin)
TRUE
CLIPS> (bload error.bin)
TRUE
CLIPS> (assert (error))
[GENRCCOM1] No such generic function <name> in function undefmethod.
This error occurs when the generic function name passed to the undefmethod function does not
exist.
Example:
CLIPS> (clear)
CLIPS> (undefmethod yak 3)
[GENRCCOM2] Expected a valid method index in function undefmethod.
This error occurs when an invalid method index is passed to undefmethod (e.g. a negative integer
or a symbol other than *).
Example:
CLIPS> (defmethod foo ())
CLIPS> (undefmethod foo a))
[GENRCCOM3] Incomplete method specification for deletion.
It is illegal to specify a non-wildcard method index when a wildcard is given for the generic
function in the function undefmethod.
Example:
CLIPS> (undefmethod * 1)
[GENRCCOM4] Cannot remove implicit system function method for generic function
<name>.
A method corresponding to a system defined function cannot be deleted.
Example:
CLIPS> (defmethod integer ((?x SYMBOL)) 0)
CLIPS> (list-defmethods integer)
integer #SYS1 (NUMBER)
integer #2 (SYMBOL)
For a total of 2 methods.
CLIPS> (undefmethod integer 1)
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[GENRCEXE1] No applicable methods for <name>.
The generic function call arguments do not satisfy any method’s parameter restrictions.
Example:
CLIPS> (defmethod foo ())
CLIPS> (foo 1 2)
[GENRCEXE2] Shadowed methods not applicable in current context.
No shadowed method is available when the function call-next-method is called.
Example:
CLIPS> (call-next-method)
[GENRCEXE3] Unable to determine class of <value> in generic function <name>.
The class or type of a generic function argument could not be determined for comparison to a
method type restriction.
Example:
CLIPS> (defmethod foo ((?a INTEGER)))
CLIPS> (foo [bogus-instance])
[GENRCEXE4] Generic function <name> method #<index> is not applicable to the given
arguments.
This error occurs when call-specific-method is called with an inappropriate set of arguments for
the specified method.
Example:
CLIPS> (defmethod foo ())
CLIPS> (call-specific-method foo 1 abc)
[GENRCFUN1] Defgeneric <name> cannot be modified while one of its methods is
executing.
Defgenerics can’t be redefined while one of their methods is currently executing.
Example:
CLIPS> (defgeneric foo)
CLIPS> (defmethod foo () (build "(defgeneric foo)"))
CLIPS> (foo)
[GENRCFUN2] Unable to find method <name> #<index> in function <name>.
No generic function method of the specified index could be found by the named function.
Example:
CLIPS> (defmethod foo 1 ())
CLIPS> (ppdefmethod foo 2)
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[GENRCFUN3] Unable to find generic function <name> in function <name>.
No generic function method of the specified index could be found by the named function.
Example:
CLIPS> (preview-generic balh)
[GENRCPSR1] Expected ')' to complete defgeneric.
A right parenthesis completes the definition of a generic function header.
Example:
CLIPS> (defgeneric foo ())
[GENRCPSR2] New method #<index1> would be indistinguishable from method
#<index2>.
An explicit index has been specified for a new method that does not match that of an older
method which has identical parameter restrictions.
Example:
CLIPS> (defmethod foo 1 ((?a INTEGER)))
CLIPS> (defmethod foo 2 ((?a INTEGER)))
[GENRCPSR3] Defgenerics are not allowed to replace constructs.
A generic function cannot have the same name as any construct.
[GENRCPSR4] Deffunction <name> imported from module <module name> conflicts with
this defgeneric.
A deffunction cannot have the same name as any generic function imported from another
module.
Example:
CLIPS> (defmodule MAIN (export ?ALL))
CLIPS> (deffunction foo ())
CLIPS> (defmodule FOO (import MAIN ?ALL))
CLIPS> (defmethod foo)
[GENRCPSR5] Generic functions are not allowed to replace deffunctions.
A generic function cannot have the same name as any deffunction.
[GENRCPSR6] Method index out of range.
A method index cannot be greater than the maximum value of an integer or less than 1.
Example:
CLIPS> (defmethod foo 0 ())
[GENRCPSR7] Expected a '(' to begin method parameter restrictions.
A left parenthesis must begin a parameter restriction list for a method.
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Example:
CLIPS> (defmethod foo)
[GENRCPSR8] Expected a variable for parameter specification.
A method parameter with restrictions must be a variable.
Example:
CLIPS> (defmethod foo ((abc)))
[GENRCPSR9] Expected a variable or '(' for parameter specification.
A method parameter must be a variable with or without restrictions.
Example:
CLIPS> (defmethod foo (abc))
[GENRCPSR10] Query must be last in parameter restriction.
A query parameter restriction must follow a type parameter restriction (if any).
Example:
CLIPS> (defmethod foo ((?a (< ?a 1) INTEGER)))
[GENRCPSR11] Duplicate classes/types not allowed in parameter restriction.
A method type parameter restriction may have only a single occurrence of a particular class.
Example:
CLIPS> (defmethod foo ((?a INTEGER INTEGER)))
[GENRCPSR12] Binds are not allowed in query expressions.
Binding new variables in a method query parameter restriction is illegal.
Example:
CLIPS> (defmethod foo ((?a (bind ?b 1))))
[GENRCPSR13] Expected a valid class/type name or query.
Method parameter restrictions consist of zero or more class names and an optional query
expression.
Example:
CLIPS> (defmethod foo ((?a 34)))
[GENRCPSR14] Unknown class/type in method.
Classes in method type parameter restrictions must already be defined.
Example:
CLIPS> (defmethod foo ((?a bogus-class)))
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[GENRCPSR15] <name> class is redundant.
All classes in a method type parameter restriction should be unrelated.
Example:
CLIPS> (defmethod foo ((?a INTEGER NUMBER)))
[GENRCPSR16] The system function <name> cannot be overloaded.
Some system functions canot be overloaded.
Example:
CLIPS> (defmethod if ())
[GENRCPSR17] Cannot replace the implicit system method #<integer>.
A system function can not be overloaded with a method that has the exact number and types of
arguments.
Example:
CLIPS> (defmethod integer ((?x NUMBER)) (* 2 ?x))
[GLOBLDEF1] Global variable <variable name> is unbound.
A global variable must be defined before it can be accessed at the command prompt or
elsewhere.
Example:
CLIPS> (clear)
CLIPS> ?*x*
[GLOBLPSR1] Global variable <variable name> was referenced, but is not defined.
A global variable must be defined before it can be accessed at the command prompt or
elsewhere.
Example:
CLIPS> (clear)
CLIPS> ?*x*
[INCRRSET1] The incremental reset behavior cannot be changed with rules loaded.
The incremental reset behaviour can only be changed when there are no currently defined rules.
[INHERPSR1] A class may not have itself as a superclass.
A class may not inherit from itself.
Example:
CLIPS> (defclass A (is-a A))
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[INHERPSR2] A class may inherit from a superclass only once.
All direct superclasses of a class must be unique.
Example:
CLIPS> (defclass A (is-a USER USER))
[INHERPSR3] A class must be defined after all its superclasses.
Subclasses must be defined last.
Example:
CLIPS> (defclass B (is-a A))
[INHERPSR4] Must have at least one superclass.
All user-defined classes must have at least one direct superclass.
Example:
CLIPS> (defclass A (is-a))
[INHERPSR5] Partial precedence list formed: <classa> <classb> … <classc>
Precedence loop in superclasses: <class1> <class2> … <classn> <class1>
No class precedence list satisfies the rules specified in section 9.3.1.1 for the given direct
superclass list. The message shows a conflict for <class1> because the precedence implies that
<class1> must both precede and succeed <class2> through <classn>. The full loop can be used
to help identify which particular classes are causing the problem. This loop is not necessarily the
only loop in the precedence list; it is the first one detected. The part of the precedence list which
was successfully formed is also listed.
Example:
CLIPS> (defclass A (is-a MULTIFIELD FLOAT SYMBOL))
CLIPS> (defclass B (is-a SYMBOL FLOAT))
CLIPS> (defclass C (is-a A B))
[INHERPSR6] A user-defined class cannot be a subclass of <name>.
The INSTANCE, INSTANCE-NAME, and INSTANCE-ADDRESS classes cannot have any
subclasses.
Example:
CLIPS> (defclass A (is-a INSTANCE))
[INSCOM1] Undefined type in function <name>.
The evaluation of an expression yielded something other than a recognized class or primitive
type.
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[INSFILE1] Function <function-name> could not completely process file <name>.
This error occurs when an instance definition is improperly formed in the input file for the
load-instances, restore-instances, or bload-instances command.
Example:
CLIPS> (load-instances bogus.txt)
[INSFILE2] <file-name> file is not a binary instances file.
or
[INSFILE3] <file-name> file is not a compatible binary instances file.
This error occurs when bload-instances attempts to load a file that was not created with
bsave-instances or when the file being loaded was created by a different version of CLIPS.
Example:
CLIPS> (reset)
CLIPS> (save-instances foo.ins)
1
CLIPS> (bload-instances foo.ins)
[INSFILE4] Function bload-instances unable to load instance <instance-name>.
This error occurs when an instance specification in the input file for the bload-instances
command could not be created.
Example:
CLIPS> (defclass A (is-a USER) (role concrete))
CLIPS> (make-instance of A)
[gen1]
CLIPS> (bsave-instances foo.bin)
1
CLIPS> (clear)
CLIPS> (defclass A (is-a USER))
CLIPS> (bload-instances foo.bin)
[INSFUN1] Expected a valid instance in function <name>.
The named function expected an instance-name or address as an argument.
Example:
CLIPS> (initialize-instance 34)
[INSFUN2] No such instance <name> in function <name>.
This error occurs when the named function cannot find the specified instance.
Example:
CLIPS> (instance-address [bogus-instance])
[INSFUN3] No such slot <name> in function <name>.
This error occurs when the named function cannot find the specified slot in an instance or class.
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Example:
CLIPS> (defclass A (is-a USER))
CLIPS> (slot-writablep A b)
[INSFUN4] Invalid instance-address in function <name>.
This error occurs when an attempt is made to use the address of a deleted instance.
Example:
CLIPS> (defclass A (is-a USER))
CLIPS> (make-instance a of A)
[a]
CLIPS> (defglobal ?*x* = (instance-address a))
CLIPS> (make-instance a of A)
[a]
CLIPS> (class ?*x*)
[INSFUN5] Cannot modify reactive instance slots while pattern-matching is in process.
CLIPS does not allow reactive instance slots to be changed while pattern-matching is taking
place. Functions used on the LHS of a rule should not have side effects (such as the changing
slot values).
Example:
CLIPS>
(defclass FOO (is-a USER)
(role concrete)
(pattern-match reactive)
(slot x (create-accessor read-write)))
CLIPS> (make-instance x of FOO)
[x]
CLIPS> (defrule BAR (x) (test (send [x] put-x 3)) =>)
CLIPS> (assert (x))
[INSFUN6] Unable to pattern-match on shared slot <name> in class <name>.
This error occurs when the number of simultaneous class hierarchy traversals is exceeded while
pattern-matching on a shared slot. See the related error message [CLASSFUN2] for more
details.
[INSFUN7] <multifield-value> illegal for single-field slot <name> of instance <name>
found in <function-call or message-handler>.
Single-field slots in an instance can hold only one atomic value.
Example:
CLIPS> (set-static-constraint-checking FALSE)
TRUE
CLIPS>
(defclass FOO (is-a USER)
(role concrete)
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(slot foo))
CLIPS>
(defmessage-handler FOO error ()
(bind ?self:foo 1 2 3))
CLIPS> (make-instance foo of FOO)
[foo]
CLIPS> (send [foo] error)
[INSFUN8] Void function illegal value for slot <name> of instance <name> found in
<function-call or message-handler>.
Only functions which have a return value can be used to generate values for an instance slot.
Example:
CLIPS> (set-static-constraint-checking FALSE)
TRUE
CLIPS>
(defclass FOO (is-a USER)
(role concrete)
(slot foo))
CLIPS>
(defmessage-handler FOO error ()
(bind ?self:foo (instances)))
CLIPS> (make-instance foo of FOO)
[foo]
CLIPS> (send [foo] error)
[INSMNGR1] Expected a valid name for new instance.
make-instance expects a symbol or an instance-name for the name of a new instance.
Example:
CLIPS> (make-instance 34 of A)
[INSMNGR2] Expected a valid class name for new instance.
make-instance expects a symbol for the class of a new instance.
Example:
CLIPS> (make-instance a of 34)
[INSMNGR3] Cannot create instances of abstract class <name>.
Direct instances of abstract classes, such as the predefined system classes, are illegal.
Example:
CLIPS> (make-instance [foo] of USER)
[INSMGNR4] The instance <name> has a slot-value which depends on the instance
definition.
The initialization of an instance is recursive in that a slot-override or default-value tries to create
or reinitialize the same instance.
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Example:
CLIPS>
(defclass A (is-a USER)
(slot foo))
CLIPS>
(make-instance a of A (foo (make-instance a of A)))
[INSMNGR5] Unable to delete old instance <name>.
make-instance will attempt to delete an old instance of the same name if it exists. This error
occurs if that deletion fails.
Example:
CLIPS> (defclass A (is-a USER))
CLIPS>
(defmessage-handler A delete around ()
(if (neq (instance-name ?self) [a]) then
(call-next-handler)))
CLIPS> (make-instance a of A)
CLIPS> (make-instance a of A)
[INSMNGR6] Cannot delete instance <name> during initialization.
The evaluation of a slot-override in make-instance or initialize-instance attempted to delete the
instance.
Example:
CLIPS>
(defclass A (is-a USER)
(slot foo))
CLIPS>
(defmessage-handler A put-foo after ($?any)
(delete-instance))
CLIPS> (make-instance a of A (foo 2))
[INSMNGR7] Instance <name> is already being initialized.
An instance cannot be reinitialized during initialization.
Example:
CLIPS> (defclass A (is-a USER))
CLIPS> (make-instance a of A)
CLIPS>
(defmessage-handler A init after ()
(initialize-instance ?self))
CLIPS> (initialize-instance a)
CLIPS> (send [a] try)
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[INSMNGR8] An error occurred during the initialization of instance <name>.
This message is displayed when an evaluation error occurs while the init message is executing
for an instance.
[INSMNGR9] Expected a valid slot name for slot-override.
make-instance and initialize-instance expect symbols for slot names.
Example:
CLIPS> (defclass A (is-a USER))
CLIPS> (make-instance a of A (34 override-value))
[INSMNGR10] Cannot create instances of reactive classes while pattern-matching is in
process.
CLIPS does not allow instances of reactive classes to be created while pattern-matching is taking
place. Functions used on the LHS of a rule should not have side effects (such as the creation of a
new instance or fact).
Example:
CLIPS> (defclass FOO (is-a USER) (role concrete) (pattern-match reactive))
CLIPS> (defrule BAR (x) (test (make-instance of FOO)) =>)
CLIPS> (assert (x))
[INSMNGR11] Invalid module specifier in new instance name.
This error occurs when the module specifier in the instance-name is illegal (such as an undefined
module name).
Example:
CLIPS> (defclass FOO (is-a USER) (role concrete))
CLIPS> (make-instance BOGUS::x of FOO)
[INSMNGR12] Cannot delete instances of reactive classes while pattern-matching is in
process.
CLIPS does not allow instances of reactive classes to be deleted while pattern-matching is taking
place. Functions used on the LHS of a rule should not have side effects (such as the deletion of a
new instance or the retraction of a fact).
Example:
CLIPS> (defclass FOO (is-a USER) (role concrete) (pattern-match reactive))
CLIPS> (make-instance x of FOO)
[x]
CLIPS> (defrule BAR (x) (test (send [x] delete)) =>)
CLIPS> (assert (x))
[INSMNGR13] Slot <slot-name> does not exist in instance <instance-name>.
This error occurs when the slot name of a slot override does not correspond to any of the valid
slot names for an instance.
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Example:
CLIPS> (defclass FOO (is-a USER) (role concrete))
CLIPS> (make-instance of FOO (x 3))
[INSMNGR14] Override required for slot <slot-name> in instance <instance-name>.
If the ?NONE keyword was specified with the default attribute for a slot, then a slot override
must be provided when an instance containing that slot is created.
Example:
CLIPS> (defclass FOO (is-a USER)
(role concrete)
(slot x (default ?NONE)))
CLIPS> (make-instance of FOO)
[INSMNGR15] init-slots not valid in this context.
The special function init-slots (for initializing slots of an instance to the class default values) can
only be called during the dispatch of an init message for an instance, i.e., in an init
message-handler.
Example:
CLIPS>
(defmessage-handler INITIAL-OBJECT error ()
(init-slots))
CLIPS> (reset)
CLIPS> (send [initial-object] error)
[INSMODDP1] Direct/message-modify message valid only in modify-instance.
The direct-modify and message-modify message-handlers attached to the class USER can only
be called as a result of the appropriate message being sent.by the modify-instance or
message-modify-instance functions. Additional handlers may be defined, but the message can
only be sent in this context.
Example:
CLIPS> (reset)
CLIPS> (send [initial-object] direct-modify 0)
[INSMODDP2] Direct/message-duplicate message valid only in duplicate-instance.
The direct-duplicate and message-duplicate message-handlers attached to the class USER can
only be called as a result of the appropriate message being sent.by the duplicate-instance or
message-duplicate-instance functions. Additional handlers may be defined, but the message can
only be sent in this context.
Example:
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CLIPS> (reset)
CLIPS> (send [initial-object] direct-duplicate 0 0)
[INSMODDP3] Instance copy must have a different name in duplicate-instance.
If an instance-name is specified for the new instance in the call to duplicate-instance, it must be
different from the source instance’s name.
Example:
CLIPS> (reset)
CLIPS> (duplicate-instance initial-object to initial-object)
[INSMULT1] Function <name> cannot be used on single-field slot <name> in instance
<name>.
The functions described in section 12.13.4.12, such as slot-insert$, can only operate on
multifield slots.
Example:
CLIPS>
(defclass A (is-a USER)
(slot foo))
CLIPS> (make-instance a of A)
[a]
CLIPS> (slot-insert$ a foo 1 abc def)
[INSQYPSR1] Duplicate instance-set member variable name in function <name>.
Instance-set member variables in an instance-set query function must be unique.
Example:
CLIPS> (any-instancep ((?a OBJECT) (?a OBJECT)) TRUE)
[INSQYPSR2] Binds are not allowed in instance-set query in function <name>.
An instance-set query cannot bind variables.
Example:
CLIPS>
(any-instancep ((?a OBJECT) (?b OBJECT))
(bind ?c 1))
[INSQYPSR3] Cannot rebind instance-set member variable <name> in function <name>.
Instance-set member variables cannot be changed within the actions of an instance-set query
function.
Example:
CLIPS>
(do-for-all-instances ((?a USER))
(if (slot-existp ?a age) then
(> ?a:age 30))
(bind ?a (send ?a get-brother)))
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[IOFUN1] Illegal logical name used for <function name> function.
A logical name must be either a symbol, string, instance-name, float, or integer.
Example:
(printout (create$ a b c) x)
[IOFUN2] Logical name <logical name> already in use.
A logical name cannot be associated with two different files.
Example:
CLIPS> (open "foo.txt" foo "w")
TRUE
CLIPS> (open "foo2.txt" foo "w")
[MEMORY1] Out of memory
This error indicates insufficient memory exists to expand internal structures enough to allow
continued operation (causing an exit to the operating system).
[MEMORY2] Release error in genfree
This error indicates a problem in the memory management routines.
[MEMORY3] Unable to allocate memory block > 32K
This error occurs when the bload function attempts to allocate a block of memory larger than
32K and the operating system does not permit blocks greater than 32K to be allocated. This will
only occur on machines which have 2 byte integers (excluding the Macintosh and IBM PC which
have machine dependent code provided so that they can allocate more than 32K). When this
error occurs, CLIPS exits to the operating system.
[MISCFUN1] expand$ must be used in the argument list of a function call.
The expand$ function may not be called unless it is within the argument list of another function.
Example:
CLIPS> (expand$ (create$ a b c))
[MODULDEF1] Illegal use of the module specifier.
The module specifier can only be used as part of a defined construct’s name or as an argument to
a function.
Example:
CLIPS> (deffunction y ())
CLIPS> (MAIN::y)
[MODULPSR1] Module <module name> does not export any constructs.
or
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[MODULPSR1] Module <module name> does not export any <construct type> constructs.
or
[MODULPSR1] Module <module name> does not export the <construct type> <construct
name>.
A construct cannot be imported from a module unless the defmodule exports that construct.
Example:
CLIPS> (clear)
CLIPS> (defmodule BAR)
CLIPS> (deftemplate BAR::bar)
CLIPS> (defmodule FOO (import BAR deftemplate bar)))
[MSGCOM1] Incomplete message-handler specification for deletion.
It is illegal to specify a non-wildcard handler index when a wildcard is given for the class in the
external C function UndefmessageHandler(). This error can only be generated when a
user-defined external function linked with CLIPS calls this function incorrectly.
[MSGCOM2] Unable to find message-handler <name> <type> for class <name> in function
<name>.
This error occurs when the named function cannot find the specified message-handler.
Example:
CLIPS> (ppdefmessage-handler USER foo around)
[MSGCOM3] Unable to delete message-handlers.
This error occurs when a message-handler can’t be deleted (such as when a binary image is
loaded).
Example:
CLIPS> (defclass FOO (is-a USER) (role concrete))
CLIPS> (defmessage-handler FOO bar ())
CLIPS> (bsave foo.bin)
TRUE
CLIPS> (bload foo.bin)
TRUE
CLIPS> (undefmessage-handler FOO bar)
[MSGFUN1] No applicable primary message-handlers found for <message>.
No primary message-handler attached to the object’s classes matched the name of the message.
Example:
CLIPS> (defclass A (is-a USER))
CLIPS> (make-instance a of A)
[a]
CLIPS> (send [a] bogus-message)
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[MSGFUN2] Message-handler <name> <type> in class <name> expected exactly/at least
<number> argument(s).
The number of message arguments was inappropriate for one of the applicable
message-handlers.
Example:
CLIPS> (defclass A (is-a USER))
CLIPS> (defmessage-handler USER foo (?a ?b))
CLIPS> (make-instance a of A)
[a]
CLIPS> (send [a] foo)
[MSGFUN3] <name> slot in instance <name>: write access denied.
This error occurs when an attempt is made to change the value of a read-only slot.
Example:
CLIPS>
(defclass A (is-a USER)
(slot foo (default 100)
(read-only)))
CLIPS> (make-instance a of A)
[a]
CLIPS> (send [a] put-foo)
[MSGFUN4] <function> may only be called from within message-handlers.
The named function operates on the active instance of a message and thus can only be called by
message-handlers.
Example:
CLIPS> (ppinstance)
[MSGFUN5] <function> operates only on instances.
The named function operates on the active instance of a message and can only handle instances
of user-defined classes (not primitive type objects).
Example:
CLIPS>
(defmessage-handler INTEGER print ()
(ppinstance))
CLIPS> (send 34 print)
[MSGFUN6] Private slot <slot-name> of class <class-name> cannot be accessed directly by
handlers attached to class <class-name>
A subclass which inherits private slots from a superclass may not access those slots using the
?self variable. This error can also occur when a superclass tries to access via dynamic-put or
dynamic-get a private slot in a subclass.
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Appendix F: CLIPS Error Messages
Example:
CLIPS> (defclass FOO (is-a USER) (role concrete) (slot x))
CLIPS> (defclass BAR (is-a FOO))
CLIPS> (defmessage-handler BAR yak () ?self:x)
[MSGFUN7] Unrecognized message-handler type in defmessage-handler.
Allowed message-handler types include primary, before, after, and around.
Example:
CLIPS> (defmessage-handler USER foo behind ())
[MSGFUN8] Unable to delete message-handler(s) from class <name>.
This error occurs when an attempt is made to delete a message-handler attached to a class for
which any of the message-handlers are executing.
Example:
CLIPS> (reset)
CLIPS>
(defmessage-handler INITIAL-OBJECT error ()
(undefmessage-handler INITIAL-OBJECT error primary))
CLIPS> (send [initial-object] error)
[MSGPASS1] Shadowed message-handlers not applicable in current context.
No shadowed message-handler is available when the function call-next-handler or
override-next-handler is called.
Example:
CLIPS> (call-next-handler)
[MSGPASS2] No such instance <name> in function <name>.
This error occurs when the named function cannot find the specified instance.
Example:
CLIPS> (instance-address [bogus-instance])
[MSGPASS3] Static reference to slot <name> of class <name> does not apply to
<instance-name> of <class-name>.
This error occurs when a static reference to a slot in a superclass by a message-handler attached
to that superclass is incorrectly applied to an instance of a subclass which redefines that slot.
Static slot references always refer to the slot defined in the class to which the message-handler is
attached.
Example:
CLIPS>
(defclass A (is-a USER)
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(slot foo))
CLIPS>
(defclass B (is-a A)
(role concrete)
(slot foo))
CLIPS>
(defmessage-handler A access-foo ()
?self:foo)
CLIPS> (make-instance b of B)
[b]
CLIPS> (send [b] access-foo)
[MSGPSR1] A class must be defined before its message-handlers.
A message-handler can only be attached to an existing class.
Example:
CLIPS> (defmessage-handler bogus-class foo ())
[MSGPSR2] Cannot (re)define message-handlers during execution of other
message-handlers for the same class.
No message-handlers for a class can be loaded while any current message-handlers attached to
the class are executing.
Example:
CLIPS> (defclass A (is-a USER))
CLIPS> (make-instance a of A)
[a]
CLIPS>
(defmessage-handler A build-new ()
(build "(defmessage-handler A new ())"))
CLIPS> (send [a] build-new)
[MSGPSR3] System message-handlers may not be modified.
There are four primary message-handlers attached to the class USER which cannot be modified:
init, delete, create and print.
Example:
CLIPS> (defmessage-handler USER init ())
[MSGPSR4] Illegal slot reference in parameter list.
Direct slot references are allowed only within message-handler bodies.
Example:
CLIPS> (defmessage-handler USER foo (?self:bar))
[MSGPSR5] Active instance parameter cannot be changed.
?self is a reserved parameter for the active instance.
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Appendix F: CLIPS Error Messages
Example:
CLIPS>
(defmessage-handler USER foo ()
(bind ?self 1))
[MSGPSR6] No such slot <name> in class <name> for ?self reference.
The symbol following the ?self: reference must be a valid slot for the class.
Example:
CLIPS> (defclass FOO (is-a USER) (role concrete) (slot x))
CLIPS> (defmessage-handler FOO bar () ?self:y)
[MSGPSR7] Illegal value for ?self reference.
The symbol following the ?self: reference must be a symbol.
Example:
CLIPS> (defclass FOO (is-a USER) (role concrete) (slot x))
CLIPS> (defmessage-handler FOO bar () ?self:7)
[MSGPSR8] Message-handlers cannot be attached to the class <name>.
Message-handlers cannot be attached to the INSTANCE, INSTANCE-ADDRESS, or
INSTANCE-NAME classes.
Example:
CLIPS> (defmessage-handler INSTANCE foo ())
[MULTIFUN1] Multifield index <index> out of range 1..<end range> in function <name>
or
[MULTIFUN1] Multifield index range <start>...<end> out of range 1..<end range> in
function <name>
This error occurs when a multifield manipulation function is passed a single index or range of
indices that does not fall within the specified range of allowed indices.
Example:
CLIPS> (delete$ (create$ a b c) 4 4)
[MULTIFUN2] Cannot rebind field variable in function progn$.
The field variable (if specified) cannot be rebound within the body of the progn$ function.
Example:
CLIPS> (progn$ (?field (create$ a)) (bind ?field 3))
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[OBJRTBLD1] No objects of existing classes can satisfy pattern.
No objects of existing classes could possibly satisfy the pattern. This error usually occurs when a
restriction placed on the is-a attribute is incompatible with slot restrictions before it in the
pattern.
Example:
CLIPS> (defclass A (is-a INITIAL-OBJECT) (slot foo))
CLIPS> (defrule error (object (foo ?) (is-a ~A)) =>)
[OBJRTBLD2] No objects of existing classes can satisfy <attribute-name> restriction in
object pattern.
The restrictions on <attribute> are such that no objects of existing classes (which also satisfy
preceding restrictions) could possibly satisfy the pattern.
Example:
CLIPS> (defrule error (object (bad-slot ?)) =>)
[OBJRTBLD3] No objects of existing classes can satisfy pattern #<pattern-num>.
No objects of existing classes could possibly satisfy the pattern. This error occurs when the
constraints for a slot as given in the defclass(es) are incompatible with the constraints imposed
by the pattern.
Example:
CLIPS>
(defclass FOO (is-a INITIAL-OBJECT)
(slot bar (type INTEGER)))
CLIPS>
(defclass BAR (is-a INITIAL-OBJECT)
(slot bar (type SYMBOL))
(slot woz))
CLIPS>
(defrule error
(x abc)
(object (bar 100) (woz ?))
(y def)
=>)
[OBJRTBLD4] Multiple restrictions on attribute <attribute-name> not allowed.
Only one restriction per attribute is allowed per object pattern.
Example:
CLIPS> (defrule error (object (is-a ?) (is-a ?)) =>)
[OBJRTBLD5] Undefined class in object pattern.
Object patterns are applicable only to classes of objects which are already defined.
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Appendix F: CLIPS Error Messages
Example:
CLIPS> (defrule error (object (is-a BOGUS)) =>)
[OBJRTMCH1] This error occurred in the object pattern network
Currently active instance: <instance-name>
Problem resides in slot <slot name> field #<field-index>
Of pattern #<pattern-number> in rule(s):
<problem-rules>+
This error pinpoints other evaluation errors associated with evaluating an expression within the
object pattern network. The specific pattern and field of the problem rules are identified.
[PATTERN1] The symbol <symbol name> has special meaning and may not be used as a
<use name>.
Certain keywords have special meaning to CLIPS and may not be used in situations that would
cause an ambiguity.
Example:
CLIPS> (deftemplate exists (slot x))
[PATTERN2] Single and multifield constraints cannot be mixed in a field constraint
Single and multifield variable constraints cannot be mixed in a field constraint (this restriction
does not include variables passed to functions with the predicate or return value constraints).
Example:
CLIPS> (defrule foo (a ?x $?y ?x&~$?y) =>)
[PRCCODE1] Attempted to call a <construct> which does not exist.
In a CLIPS configuration without deffunctions and/or generic functions, an attempt was made to
call a deffunction or generic function from a binary image generated by the bsave command.
[PRCCODE2] Functions without a return value are illegal as <construct> arguments.
An evaluation error occurred while examining the arguments for a deffunction, generic function
or message.
Example:
CLIPS> (defmethod foo (?a))
CLIPS> (foo (instances))
[PRCCODE3] Undefined variable <name> referenced in <where>.
Local variables in the actions of a deffunction, method, message-handler, or defrule must
reference parameters, variables bound within the actions with the bind function, or variables
bound on the LHS of a rule.
Example:
CLIPS> (defrule foo => (+ ?a 3))
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[PRCCODE4] Execution halted during the actions of <construct> <name>.
This error occurs when the actions of a rule, deffunction, generic function method or
message-handler are prematurely aborted due to an error.
[PRCCODE5] Variable <name> unbound [in <construct> <name>].
This error occurs when local variables in the actions of a deffunction, method, message-handler,
or defrule becomes unbound during execution as a result of calling the bind function with no
arguments.
Example:
CLIPS> (deffunction foo () (bind ?a) ?a)
CLIPS> (foo)
[PRCCODE6] This error occurred while evaluating arguments for the <construct>
<name>.
An evaluation error occurred while examining the arguments for a deffunction, generic function
method or message-handler.
Example:
CLIPS> (deffunction foo (?a))
CLIPS> (foo (+ (eval "(gensym)") 2))
[PRCCODE7] Duplicate parameter names not allowed.
Deffunction, method or message-handler parameter names must be unique.
Example:
CLIPS> (defmethod foo ((?x INTEGER) (?x FLOAT)))
[PRCCODE8] No parameters allowed after wildcard parameter.
A wildcard parameter for a deffunction, method or message-handler must be the last parameter.
Example:
CLIPS> (defmethod foo (($?x INTEGER) (?y SYMBOL)))
[PRCDRPSR1] Cannot rebind count variable in function loop-for-count.
The special variable ?count cannot be rebound within the body of the loop-for-count function.
Example:
CLIPS> (loop-for-count (?count 10) (bind ?count 3))
[PRCDRPSR2] The return function is not valid in this context.
or
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Appendix F: CLIPS Error Messages
[PRCDRPSR2] The break function is not valid in this context.
The return and break functions can only be used within certain contexts (e.g. the break function
can only be used within a while loop and certain instance set query functions).
Example:
CLIPS> (return 3)
[PRCDRPSR3] Duplicate case found in switch function.
A case may be specified only once in a switch statement.
Example:
CLIPS> (switch a (case a then 8) (case a then 9))
[PRNTUTIL1] Unable to find <item> <item-name>
This error occurs when CLIPS cannot find the named item (check for typos).
[PRNTUTIL2] Syntax Error: Check appropriate syntax for <item>
This error occurs when the appropriate syntax is not used.
Example:
CLIPS> (if (> 3 4))
[PRNTUTIL3]
*** CLIPS SYSTEM ERROR ***
ID = <error-id>
CLIPS data structures are in an inconsistent or corrupted state.
This error may have occurred from errors in user defined code.
**************************
This error indicates an internal problem within CLIPS (which may have been caused by user
defined functions or other user code). If the problem cannot be located within user defined code,
then the <error-id> should be reported.
[PRNTUTIL4] Unable to delete <item> <item-name>
This error occurs when CLIPS cannot delete the named item (e.g. a construct might be in use).
One example which will cause this error is an attempt to delete a deffunction or generic function
which is used in another construct (such as the RHS of a defrule or a default-dynamic facet of a
defclass slot).
[PRNTUTIL5] The <item> has already been parsed.
This error occurs when CLIPS has already parsed an attribute or declaration.
[PRNTUTIL6] Local variables cannot be accessed by <function or construct>.
This error occurs when a local variable is used by a function or construct that cannot use global
variables.
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Example:
CLIPS> (deffacts info (fact ?x))
[PRNTUTIL7] Attempt to divide by zero in <function-name> function.
This error occurs when a function attempts to divide by zero.
Example:
CLIPS> (/ 3 0)
[ROUTER1] Logical name <logical_name> was not recognized by any routers
This error results because "Hello" is not recognized as a valid router name.
Example:
CLIPS> (printout "Hello" crlf)
[RULECSTR1] Variable <variable name> in CE #<integer> slot <slot name>
has constraint conflicts which make the pattern unmatchable.
or
[RULECSTR1] Variable <variable name> in CE #<integer> field #<integer>
has constraint conflicts which make the pattern unmatchable.
or
[RULECSTR1] CE #<integer> slot <slot name>
has constraint conflicts which make the pattern unmatchable.
or
[RULECSTR1] CE #<integer> field #<integer>
has constraint conflicts which make the pattern unmatchable.
This error occurs when slot value constraints (such as allowed types) prevents any value from
matching the slot constraint for a pattern.
Example:
CLIPS> (deftemplate foo (slot x (type SYMBOL)))
CLIPS> (deftemplate bar (slot x (type FLOAT)))
CLIPS> (defrule yak (foo (x ?x)) (bar (x ?x)) =>)
[RULECSTR2] Previous variable bindings of <variable name> caused the type restrictions
for argument #<integer> of the expression <expression>
found in CE#<integer> slot <slot name> to be violated.
This error occurs when previous variable bindings and constraints prevent a variable from
containing a value which satisfies the type constraints for one of a function’s parameters.
Example:
CLIPS> (deftemplate foo (slot x (type SYMBOL)))
CLIPS> (defrule bar (foo (x ?x&:(> ?x 3))) =>)
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Appendix F: CLIPS Error Messages
[RULECSTR3] Previous variable bindings of <variable name> caused the type restrictions
for argument #<integer> of the expression <expression>
found in the rule's RHS to be violated.
This error occurs when previous variable bindings and constraints prevent a variable from
containing a value which satisfies the type constraints for one of a function’s parameters.
Example:
CLIPS> (deftemplate foo (slot x (type SYMBOL)))
CLIPS> (defrule bar (foo (x ?x)) => (printout t (+ ?x 1) crlf))
[RULELHS1] The logical CE cannot be used with a not/exists/forall CE.
Logical CEs can be placed outside, but not inside, a not/exists/forall CE.
Example:
CLIPS> (defrule error (not (logical (x))) =>)
[RULELHS2] A pattern CE cannot be bound to a pattern-address within a not CE
This is an illegal operation and results in an error message.
Example:
CLIPS> (defrule error (not ?f <- (fact)) =>)
[RULEPSR1] Logical CEs must be placed first in a rule
If logical CEs are used, then the first CE must be a logical CE.
Example:
CLIPS> (defrule error (a) (logical (b)) =>)
[RULEPSR2] Gaps may not exist between logical CEs
Logical CEs found within a rule must be contiguous.
Example:
CLIPS> (defrule error (logical (a)) (b) (logical (c)) =>)
[STRNGFUN1] Function build does not work in run time modules.
or
[STRNGFUN1] Function eval does not work in run time modules.
The build and eval functions do not work in run time modules because the code required for
parsing is not available.
[STRNGFUN2] Some variables could not be accessed by the eval function.
Local variables cannot be accessed by the eval function.
Example:
CLIPS> (eval "?x")
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[SYSDEP1] No file found for -f option
This message occurs if the -f option is used when executing CLIPS, but no arguments are
provided.
Example:
clips -f
[TEXTPRO1] Could not open file <file-name>.
This error occurs when the external text-processing system command fetch encounters an error
when loading a file.
Example:
CLIPS> (fetch “bogus.txt”)
[TMPLTDEF1] Invalid slot <slot name> not defined in corresponding deftemplate
<deftemplate name>
The slot name supplied does not correspond to a slot name defined in the corresponding
deftemplate
Example:
CLIPS> (deftemplate example (slot x))
CLIPS> (defrule error (example (z 3)) =>)
[TMPLTDEF2] The single field slot <slot name> can only contain a single field value.
If a slot definition is specified in a template pattern or fact, the contents of the slot must be
capable of matching against or evaluating to a single value.
Example:
CLIPS> (deftemplate example (slot x))
CLIPS> (assert (example (x)))
[TMPLTFUN1] Fact-indexes can only be used by <command name> as a top level
command.
Fact indexes may only be used with the modify and duplicate commands when the command is
issued from the top-level command prompt.
Example:
CLIPS> (defrule foo => (modify 1 (x 3))
[TMPLTFUN2] Attempted to assert a multifield value into the single field slot <slot name>
of deftemplate <deftemplate name>.
A multifield value cannot be stored in a single field slot.
Example:
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Appendix F: CLIPS Error Messages
CLIPS> (deftemplate foo (slot x))
CLIPS>
(defrule foo
=>
(bind ?x (create$ a b))
(assert (foo (x ?x))))
CLIPS> (reset)
CLIPS> (run)
[TMPLTRHS1] Slot <slot name> requires a value because of its (default ?NONE) attribute.
The (default ?NONE) attribute requires that a slot value be supplied whenever a new fact is
created.
Example:
CLIPS> (deftemplate foo (slot x (default ?NONE)))
CLIPS> (assert (foo))
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Appendix G:
CLIPS BNF
Data Types
<symbol> ::= A valid symbol as specified
in section 2.3.1
<string> ::= A valid string as specified
in section 2.3.1
<float> ::= A valid float as specified
in section 2.3.1
<integer> ::= A valid integer as specified
in section 2.3.1
<instance-name> ::= A valid instance-name as specified
in section 2.3.1
<number> ::= <float> | <integer>
<lexeme> ::= <symbol> | <string>
<constant> ::= <symbol> | <string> | <integer> |
<float> | <instance-name>
<comment> ::= <string>
<variable-symbol> ::= A symbol beginning with an
alphabetic character
<function-name> ::= Any symbol which corresponds to a
system or user defined function, a
deffunction name, or a defgeneric
name
<file-name> ::= A symbol or string which is a valid
file name (including path
information) for the operating
system under which CLIPS is running
<slot-name> ::= A valid deftemplate slot name
<...-name> ::= A <symbol> where the ellipsis
indicate what the symbol represents.
For example, <rule-name> is a symbol
which represents the name of a rule.
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Appendix G: CLIPS BNF
Variables and Expressions
<single-field-variable> ::= ?<variable-symbol>
<multifield-variable> ::= $?<variable-symbol>
<global-variable> ::= ?*<symbol>*
<variable> ::= <single-field-variable> |
<multifield-variable> |
<global-variable>
<function-call> ::= (<function-name> <expression>*)
<expression> ::= <constant> | <variable> |
<function-call>
<action> ::= <expression>
<...-expression> ::= An <expression> which returns
the type indicated by the
ellipsis. For example,
<integer-expression> should
return an integer.
Constructs
<CLIPS-program> ::= <construct>*
<construct> ::= <deffacts-construct> |
<deftemplate-construct> |
<defglobal-construct> |
<defrule-construct> |
<deffunction-construct> |
<defgeneric-construct> |
<defmethod-construct> |
<defclass-construct> |
<definstance-construct> |
<defmessage-handler-construct> |
<defmodule-construct>
Deffacts Construct
<deffacts-construct> ::= (deffacts <deffacts-name> [<comment>]
<RHS-pattern>*)
Deftemplate Construct
<deftemplate-construct>
::= (deftemplate <deftemplate-name>
[<comment>]
<slot-definition>*)
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<slot-definition> ::= <single-slot-definition> |
<multislot-definition>
<single-slot-definition>
::= (slot <slot-name> <template-attribute>*)
<multislot-definition>
::= (multislot <slot-name>
<template-attribute>*)
<template-attribute>
::= <default-attribute> |
<constraint-attribute>
<default-attribute>
::= (default ?DERIVE | ?NONE | <expression>*) |
(default-dynamic <expression>*)
Fact Specification
<RHS-pattern> ::= <ordered-RHS-pattern> |
<template-RHS-pattern>
<ordered-RHS-pattern> ::= (<symbol> <RHS-field>+)
<template-RHS-pattern> ::= (<deftemplate-name> <RHS-slot>*)
<RHS-slot> ::= <single-field-RHS-slot> |
<multifield-RHS-slot>
<single-field-RHS-slot> ::= (<slot-name> <RHS-field>)
<multifield-RHS-slot> ::= (<slot-name> <RHS-field>*)
<RHS-field> ::= <variable> |
<constant> |
<function-call>
Defrule Construct
<defrule-construct> ::= (defrule <rule-name> [<comment>]
[<declaration>]
<conditional-element>*
=>
<action>*)
<declaration> ::= (declare <rule-property>+)
<rule-property> ::= (salience <integer-expression>) |
(auto-focus <boolean-symbol>)
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Appendix G: CLIPS BNF
<boolean-symbol> ::= TRUE | FALSE
<conditional-element> ::= <pattern-CE> |
<assigned-pattern-CE> |
<not-CE> | <and-CE> | <or-CE> |
<logical-CE> | <test-CE> |
<exists-CE> | <forall-CE>
<pattern-CE> ::= <ordered-pattern-CE> |
<template-pattern-CE> |
<object-pattern-CE>
<assigned-pattern-CE> ::= <single-field-variable> <- <pattern-CE>
<not-CE> ::= (not <conditional-element>)
<and-CE> ::= (and <conditional-element>+)
<or-CE> ::= (or <conditional-element>+)
<logical-CE> ::= (logical <conditional-element>+)
<test-CE> ::= (test <function-call>)
<exists-CE> ::= (exists <conditional-element>+)
<forall-CE> ::= (forall <conditional-element>
<conditional-element>+)
<ordered-pattern-CE> ::= (<symbol> <constraint>*)
<template-pattern-CE> ::= (<deftemplate-name> <LHS-slot>*)
<object-pattern-CE> ::= (object <attribute-constraint>*)
<attribute-constraint> ::= (is-a <constraint>) |
(name <constraint>) |
(<slot-name> <constraint>*)
<LHS-slot> ::= <single-field-LHS-slot> |
<multifield-LHS-slot>
<single-field-LHS-slot> ::= (<slot-name> <constraint>)
<multifield-LHS-slot> ::= (<slot-name> <constraint>*)
<constraint> ::= ? | $? | <connected-constraint>
<connected-constraint>
::= <single-constraint> |
<single-constraint> & <connected-constraint> |
<single-constraint> | <connected-constraint>
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<single-constraint> ::= <term> | ~<term>
<term> ::= <constant> |
<single-field-variable> |
<multifield-variable> |
:<function-call> |
=<function-call>
Defglobal Construct
<defglobal-construct> ::= (defglobal [<defmodule-name>]
<global-assignment>*)
<global-assignment> ::= <global-variable> = <expression>
<global-variable> ::= ?*<symbol>*
Deffunction Construct
<deffunction-construct>
::= (deffunction <name> [<comment>]
(<regular-parameter>* [<wildcard-parameter>])
<action>*)
<regular-parameter> ::= <single-field-variable>
<wildcard-parameter> ::= <multifield-variable>
Defgeneric Construct
<defgeneric-construct> ::= (defgeneric <name> [<comment>])
Defmethod Construct
<defmethod-construct>
::= (defmethod <name> [<index>] [<comment>]
(<parameter-restriction>*
[<wildcard-parameter-restriction>])
<action>*)
<parameter-restriction>
::= <single-field-variable> |
(<single-field-variable> <type>* [<query>])
<wildcard-parameter-restriction>
::= <multifield-variable> |
(<multifield-variable> <type>* [<query>])
<type> ::= <class-name>
<query> ::= <global-variable> | <function-call>
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Appendix G: CLIPS BNF
Defclass Construct
<defclass-construct> ::= (defclass <name> [<comment>]
(is-a <superclass-name>+)
[<role>]
[<pattern-match-role>]
<slot>*
<handler-documentation>*)
<role> ::= (role concrete | abstract)
<pattern-match-role>
::= (pattern-match reactive | non-reactive)
<slot> ::= (slot <name> <facet>*) |
(single-slot <name> <facet>*) |
(multislot <name> <facet>*)
<facet> ::= <default-facet> | <storage-facet> |
<access-facet> | <propagation-facet> |
<source-facet> | <pattern-match-facet> |
<visibility-facet> | <create-accessor-facet>
<override-message-facet> | <constraint-attribute>
<default-facet> ::=
(default ?DERIVE | ?NONE | <expression>*) |
(default-dynamic <expression>*)
<storage-facet> ::= (storage local | shared)
<access-facet>
::= (access read-write | read-only | initialize-only)
<propagation-facet> ::= (propagation inherit | no-inherit)
<source-facet> ::= (source exclusive | composite)
<pattern-match-facet>
::= (pattern-match reactive | non-reactive)
<visibility-facet> ::= (visibility private | public)
<create-accessor-facet>
::= (create-accessor ?NONE | read | write | read-write)
<override-message-facet>
::= (override-message ?DEFAULT | <message-name>)
<handler-documentation>
::= (message-handler <name> [<handler-type>])
<handler-type> ::= primary | around | before | after
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Defmessage-handler Construct
<defmessage-handler-construct>
::= (defmessage-handler <class-name>
<message-name> [<handler-type>] [<comment>]
(<parameter>* [<wildcard-parameter>])
<action>*)
<handler-type> ::= around | before | primary | after
<parameter> ::= <single-field-variable>
<wildcard-parameter> ::= <multifield-variable>
Definstances Construct
<definstances-construct>
::= (definstances <definstances-name>
[active] [<comment>]
<instance-template>*)
<instance-template> ::= (<instance-definition>)
<instance-definition> ::= <instance-name-expression> of
<class-name-expression>
<slot-override>*
<slot-override> ::= (<slot-name-expression> <expression>*)
Defmodule Construct
<defmodule-construct> ::= (defmodule <module-name> [<comment>]
<port-specification>*)
<port-specification> ::= (export <port-item>) |
(import <module-name> <port-item>)
<port-item> ::= ?ALL |
?NONE |
<port-construct> ?ALL |
<port-construct> ?NONE |
<port-construct> <construct-name>+
<port-construct> ::= deftemplate | defclass |
defglobal | deffunction |
defgeneric
Constraint Attributes
<constraint-attribute>
::= <type-attribute> |
<allowed-constant-attribute> |
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Appendix G: CLIPS BNF
<range-attribute> |
<cardinality-attribute>
<type-attribute> ::= (type <type-specification>)
<type-specification> ::= <allowed-type>+ | ?VARIABLE
<allowed-type> ::= SYMBOL | STRING | LEXEME |
INTEGER | FLOAT | NUMBER |
INSTANCE-NAME | INSTANCE-ADDRESS |
INSTANCE | EXTERNAL-ADDRESS |
FACT-ADDRESS
<allowed-constant-attribute>
::= (allowed-symbols <symbol-list>) |
(allowed-strings <string-list>) |
(allowed-lexemes <lexeme-list> |
(allowed-integers <integer-list>) |
(allowed-floats <float-list>) |
(allowed-numbers <number-list>) |
(allowed-instance-names <instance-list>) |
(allowed-classes <class-name-list>) |
(allowed-values <value-list>)
<symbol-list> ::= <symbol>+ | ?VARIABLE
<string-list> ::= <string>+ | ?VARIABLE
<lexeme-list> ::= <lexeme>+ | ?VARIABLE
<integer-list> ::= <integer>+ | ?VARIABLE
<float-list> ::= <float>+ | ?VARIABLE
<number-list> ::= <number>+ | ?VARIABLE
<instance-name-list> ::= <instance-name>+ | ?VARIABLE
<class-name-list> ::= <class-name>+ | ?VARIABLE
<value-list> ::= <constant>+ | ?VARIABLE
<range-attribute> ::= (range <range-specification>
<range-specification>)
<range-specification> ::= <number> | ?VARIABLE
<cardinality-attribute>
::= (cardinality <cardinality-specification>
<cardinality-specification>)
<cardinality-specification>
::= <integer> | ?VARIABLE
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CLIPS Reference Manual
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393
Appendix H:
Reserved Function Names
This appendix lists all of the functions provided by either standard CLIPS or various CLIPS
extensions. They should be considered reserved function names, and users should not create
user-defined functions with any of these names.
!=
*
**
+
-
/
<
<=
<>
=
>
>=
abs
acos
acosh
acot
acoth
acsc
acsch
active-duplicate-instance
active-initialize-instance
active-make-instance
active-message-duplicate-instance
active-message-modify-instance
active-modify-instance
agenda
and
any-instancep
apropos
asec
asech
asin
asinh
assert
assert-string
atan
atanh
batch
batch*
bind
bload
bload-instances
break
browse-classes
bsave
bsave-instances
build
call-next-handler
call-next-method
call-specific-method
class
class-abstractp
class-existp
class-reactivep
class-slots
class-subclasses
class-superclasses
clear
clear-focus-stack
close
conserve-mem
constructs-to-c
cos
cosh
CLIPS Reference Manual
394
Appendix H: Reserved Function Names
cot
coth
create$
csc
csch
defclass-module
deffacts-module
deffunction-module
defgeneric-module
defglobal-module
definstances-module
defrule-module
deftemplate-module
deg-grad
deg-rad
delayed-do-for-all-instances
delete$
delete-instance
dependencies
dependents
describe-class
direct-mv-delete
direct-mv-insert
direct-mv-replace
div
do-for-all-instances
do-for-instance
dribble-off
dribble-on
duplicate
duplicate-instance
duplicate-instance
dynamic-get
dynamic-put
edit
eq
eval
evenp
exit
exp
expand$
explode$
fact-existp
fact-index
fact-relation
fact-slot-names
fact-slot-value
facts
fetch
find-all-instances
find-instance
first$
float
floatp
focus
format
gensym
gensym*
get
get-auto-float-dividend
get-current-module
get-defclass-list
get-deffacts-list
get-deffunction-list
get-defgeneric-list
get-defglobal-list
get-definstances-list
get-defmessage-handler-list
get-defmethod-list
get-defmodule-list
get-defrule-list
get-deftemplate-list
get-dynamic-constraint-checking
get-fact-duplication
get-fact-list
get-focus
get-focus-stack
get-function-restrictions
get-incremental-reset
get-method-restrictions
get-reset-globals
get-salience-evaluation
get-sequence-operator-recognition
get-static-constraint-checking
get-strategy
grad-deg
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395
halt
if
implode$
init-slots
initialize-instance
initialize-instance
insert$
instance-address
instance-addressp
instance-existp
instance-name
instance-name-to-symbol
instance-namep
instancep
instances
integer
integerp
length
length$
lexemep
list-defclasses
list-deffacts
list-deffunctions
list-defgenerics
list-defglobals
list-definstances
list-defmessage-handlers
list-defmethods
list-defmodules
list-defrules
list-deftemplates
list-focus-stack
list-watch-items
load
load*
load-facts
load-instances
log
log10
loop-for-count
lowcase
make-instance
make-instance
matches
max
mem-requests
mem-used
member
member$
message-duplicate-instance
message-duplicate-instance
message-handler-existp
message-modify-instance
message-modify-instance
min
mod
modify
modify-instance
modify-instance
multifieldp
mv-append
mv-delete
mv-replace
mv-slot-delete
mv-slot-insert
mv-slot-replace
mv-subseq
neq
next-handlerp
next-methodp
not
nth
nth$
numberp
object-pattern-match-delay
oddp
open
options
or
override-next-handler
override-next-method
pi
pointerp
pop-focus
CLIPS Reference Manual
396
Appendix H: Reserved Function Names
ppdefclass
ppdeffacts
ppdeffunction
ppdefgeneric
ppdefglobal
ppdefinstances
ppdefmessage-handler
ppdefmethod
ppdefmodule
ppdefrule
ppdeftemplate
ppinstance
preview-generic
preview-send
primitives-info
print-region
printout
progn
progn$
put
rad-deg
random
read
readline
refresh
refresh-agenda
release-mem
remove
remove-break
rename
replace$
reset
rest$
restore-instances
retract
return
round
rule-complexity
rules
run
save
save-facts
save-instances
sec
sech
seed
send
sequencep
set-auto-float-dividend
set-break
set-current-module
set-dynamic-constraint-checking
set-fact-duplication
set-incremental-reset
set-reset-globals
set-salience-evaluation
set-sequence-operator-recognition
set-static-constraint-checking
set-strategy
setgen
show-breaks
show-defglobals
show-fht
show-fpn
show-joins
show-opn
sin
sinh
slot-allowed-values
slot-cardinality
slot-delete$
slot-direct-accessp
slot-direct-delete$
slot-direct-insert$
slot-direct-replace$
slot-existp
slot-facets
slot-initablep
slot-insert$
slot-publicp
slot-range
slot-replace$
slot-sources
slot-types
slot-writablep
sqrt
CLIPS Reference Manual
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397
str-assert
str-cat
str-compare
str-explode
str-implode
str-index
str-length
stringp
sub-string
subclassp
subseq$
subset
subsetp
superclassp
switch
sym-cat
symbol-to-instance-name
symbolp
system
tan
tanh
time
toss
type
type
undefclass
undeffacts
undeffunction
undefgeneric
undefglobal
undefinstances
undefmessage-handler
undefmethod
undefrule
undeftemplate
unmake-instance
unwatch
upcase
watch
while
wordp
CLIPS Reference Manual
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399
Appendix I:
Bibliography of CLIPS Publications
Programming
Giarratano, J., and Riley, G. Expert Systems: Principles and Programming, 3rd Edition, Boston,
PWS Publishing Company, 1998.
Gonzalez, A. J., and Dankel, D. D. Engineering of Knowledge-basedSystems: Theory and
Practice, Prentice Hall, 1993.
Jackson, P. Introduction to Expert Systems, 3rd Edition, Reading, Addison-Wesley, 1998.
Reviews
Brooke, T. “The Art of Production Systems,” AI Expert, January 1992.
Brooke, T. “Software Review,” AI Expert, April 1988.
Golden, J. “Shell Review Monthly,” AI Today, March/April 1988.
Mettrey, W. “A Comparative Evaluation of Expert System Tools,” Computer, February 1991.
Popolizio, J. “CLIPS: NASA’s COSMIC Shell,” Artificial Intelligence Research, August 1,
1988.
Raeth, P. “Two PC–based Expert System Shells for the First–time Developer,” Computer,
November 1988.
Overviews
Culbert, C., et al., “A Solution to the Expert System Delivery Problem,” Proceedings of the
ISA/88, Houston, TX, October 1988.
Riley, G. “C Language Integrated Production System,” in Encyclopedia of Computer Science
and Technology, Volume 37. Edited by A. Kent and J.G. Williams. New York, Marcel Dekker,
Inc., 1997.
Riley, G. “Expert Systems Methodology,” in The Industrial Electronics Handbook. Edited by
J.D. Irwin. Boca Raton, CRC Press, 1997.
Riley, G. “CLIPS: An Expert System Building Tool,” Proceedings of the Technology 2001
Conference, San Jose, CA, December 1991.
CLIPS Reference Manual
400
Appendix I: Bibliography of CLIPS Publications
Riley, G. “CLIPS: A Tool for the Development and Delivery of Expert Systems,” Proceedings of
the Technology 2000 Conference, Washington, DC, November 1990.
Riley G., and Donnell, B. “Advanced CLIPS Capabilities,” Proceedings of The Fourth Annual
Workshop on Space Operations Applications and Research (SOAR ’90), Albuquerque, NM, June
1990.
Riley, G., et al. “CLIPS: An Expert System Tool for Training, Development, and Delivery,” in
Intelligent Systems Review, Volume 1, Number 1, Fall 1988.
Riley, G., et al., “CLIPS: An Expert System Tool for Delivery and Training,” Proceedings of the
Third Conference on Artificial Intelligence for Space Applications, Huntsville, AL, November
1987.
Applications
Carreno, L. A. and Steel, R. A. “Life Insurance Risk Assessment using a Fuzzy Logic Expert
System,” Proceedings of the North American Fuzzy Logic Processing Society (NAFIPS 1992),
Houston, TX, December 1992.
Cheatham, J. B., et al. “A Multi–Sensor System for Robotics Proximity Operations,”
Proceedings of The Second Annual Workshop on Space Operations Automation and Robotics
(SOAR ’88), Albuquerque, NM, July 1988.
Chen, Y. “Applying Knowledge–Based Expert System to Meat Grading,” Proceedings of The
Annual AI Systems in Government Conference, Washington, D.C., March 1989.
“CLIPS: A NASA Developed Expert System Tool,” NASA Tech Briefs, November/December
1987.
Dutton, T. “HUB SIAASHING: A Knowledge–Based System for Severe, Temporary Airline
Schedule Reduction,” Innovative Applications of Artificial Intelligence 4, Klahr, Philip, and
Scott, A. Carlisle ed., 1992.
Ehler, G. B. “A Multiple Knowledge-Based Spatial Decision Support System for Industrial Site
Selection,” M.S. Thesis, Department of Geography, University of South Carolina, Columbia, SC.
Fink, P., and Herren, L. T. “An Intelligent Tutoring System to Teach Interdependent Cognitive
and High Performance Skills,” Proceedings of Contributed Sessions 1991 Conference on
Intelligent Computer Aided Training, Houston, TX, November 1991.
Fink, P. “NESSUS/EXPERT: Bridging the Gap between Artificial Intelligence and FORTRAN,”
Proceedings of The Second Annual Workshop on Space Operations Automation and Robotics
(SOAR ’88), Albuquerque, NM, July 1988.
CLIPS Reference Manual
CLIPS Basic Programming Guide
401
Flamm, R. O., et al. “The Integrated Southern Pine Beetle Expert System: ISPBEX,” Expert
Systems with Applications, Vol. 2, 1991.
Franier, R., et al. “PI–in–a–Box: A Knowledge–based System for Space Science
Experimentation,” Proceedings of the Fifth Innovative Applications of Artificial Intelligence
Conference, July 11–15, 1993, Washington, D.C.
Frainier, R., et al. “PI-in-a-Box: A Knowledge-Based System for Space Science
Experimentation,” AI magazine, Volume 15, No. 1, Spring, 1994.
Frainier, R., et al. “PI in the Sky: The Astronaut Science Advisor on SLS-2,” Proceedings of The
Seventh Annual Workshop on Space Operations Applications and Research (SOAR ’93),
Houston, TX, August 1993.
Germain, D., and Desrosiers, S. “Turning Up the Heat on Space Station Training: The Active
Thermal Control System ICAT,” Proceedings of Contributed Sessions 1991 Conference on
Intelligent Computer Aided Training, Houston, TX, November 1991.
Grinstein, G. G., et al. “Virtual Environment Architecture for Rapid Application Development,”
Proceedings of The Contributed Sessions 1993 Conference on Intelligent Computer Aided
Training and Virtual Environment Technology (ICAT-VET ’93), Houston, TX, May 1993.
Haymann–Haber, G., et al. “An Expert System to Advise Astronauts During Experiments: The
Protocol Manager Module,” Proceedings of The Third Annual Workshop on Space Operations
Automation and Robotics (SOAR ’89), Houston, TX, July 1989.
Hill, T., and Faltisco, R. “Intelligent Fault Management for the Space Station Active Thermal
Control System,” Proceedings of The Fifth Annual Workshop on Space Operations Applications
and Research (SOAR ’91), Houston, TX, July 1991.
Hipwell, D. P. “Developing Realistic Cooperative Behaviors for Autonomous Agents in Air
Combat Simuation,” M.S. Thesis, Air Force Institute of Technology, Wright Patternson AFB,
Ohio, 1993.
Hughes, P. M. “CLEAR: Automating Control Centers with Expert System Technology,”
Proceedings of The Third Annual Workshop on Space Operations Automation and Robotics
(SOAR ’89), Houston, TX, July 1989.
Johnson, W. B., et al. “An Intelligent Tutoring System for Space Shuttle Diagnosis,”
Proceedings of The Second Annual Workshop on Space Operations Automation and Robotics
(SOAR ’88), Albuquerque, NM, July 1988.
Kahn, M. G., et al. “An Expert System for Culture-Based Infection Control Surveillance,”
Proceedings of The Seventeenth Annual Symposium on Computer Applications in Medical Care
(SCAMC ’93), Washington, D.C., October 1993.
CLIPS Reference Manual
402
Appendix I: Bibliography of CLIPS Publications
Kingston, J. “Pragmatic KADS: A methodological approach to a small knowledge based systems
project,” Expert Systems: The International Journal of Knowledge Engineering, 4, 4, November
1992.
Kosta, C. P., and Krolak, P. D. “Rapid Prototyping 3D Virtual World Interfaces within a Virtual
Factory Environment,” Proceedings of The Contributed Sessions 1993 Conference on Intelligent
Computer Aided Training and Virtual Environment Technology (ICAT-VET ’93), Houston, TX,
May 1993.
Kosta, C. P., and Krolak, P. D. “An Artificial Reality Environment for Remote Factory Control
and Monitoring,” Vision 21: Interdisciplinary Science and Engineering in the Era of
Cyberspace, NASA/Lewis Research Center, December 1993.
Kovarik, V. J. “Autonomously Acquiring Declarative and Procedural Domain Knowledge for
ICAT Systems,” Proceedings of The Contributed Sessions 1993 Conference on Intelligent
Computer Aided Training and Virtual Environment Technology (ICAT-VET ’93), Houston, TX,
May 1993.
Lauriente, M., et al. “Diagnosing Anomalies of Spacecraft for Space Maintenance and
Servicing,” Proceedings of The Seventh Annual Workshop on Space Operations Applications
and Research (SOAR ’93), Houston, TX, August 1993.
Lee, L., and Hill, R. W., “Process Control and Recovery in the Link Monitor and Control
Operator Assistant,” Proceedings of The Sixth Annual Workshop on Space Operations
Applications and Research (SOAR ’92), Houston, TX, August 1992.
Leinweber, D. “Finance,” Expert Systems and Artificial Intelligence: Applications and
Management, Howard W. Sams & Company, Bartee, T. C. ed., 1988.
Loftin, K. C., et al. “The Application of Integrated Knowledge–Based Systems for the
Biomedical Risk Accessment Intelligent Network (BRAIN),” Proceedings of Technology 2002:
The Third National Technology Transfer Conference and Exposition, Washington D.C.,
February 1993.
Loftin, R. B., and Savely, R.T. “Intelligent Computer Aided Training and Tutoring,”
Proceedings of the Technology 2000 Conference, Washington, DC, November 1990.
Loftin, R. B., et al. “An Intelligent Training System for Space Shuttle Flight Controllers,”
Innovative Applications of Artificial Intelligence, 1989, AAAI Press/The MIT Press, Menlo
Press, Schoor, Herbert, and Rappaport, Alain ed.
Loftin, R. B., et al. “An Intelligent Training System for Payload–Assist Module Deploys,”
Proceedings of The First Annual Workshop on Space Operations Automation and Robotics
(SOAR ’87), Houston, TX, August 1987.
CLIPS Reference Manual
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Lucas, T. S., and Lewis, G. “DISPLAVAL: An Expert System Approach for the Training of
Display Builders,” Proceedings of Contributed Sessions 1991 Conference on Intelligent
Computer Aided Training, Houston, TX, November 1991.
McCarthy, L., et al. “Spatial Considerations for Instructional Development in a Virtual
Environment,” Proceedings of The Contributed Sessions 1993 Conference on Intelligent
Computer Aided Training and Virtual Environment Technology (ICAT-VET ’93), Houston, TX,
May 1993.
“Mission Accomplished,” NASA Tech Briefs, September 1993.
Mitchell, P. “An Expert System for Shuttle and Satellite Radar Tracker Scheduling,”
Proceedings of The Second Annual Workshop on Space Operations Automation and Robotics
(SOAR ’88), Albuquerque, NM, July 1988.
Mitchell, R. “Expert Systems and Air–Combat Simulation,” AI Expert, September 1989.
Mortenson, P. “Predicting Wind Shear from the Dispatch Office,” Airline Executive, April 1988.
Mueller, S. “Development of a Personal–Computer–Based Intelligent Tutoring System,”
Proceedings of The Second Annual Workshop on Space Operations Automation and Robotics
(SOAR ’88), Albuquerque, NM, July 1988.
Muratore, J., et al. “Space Shuttle Telemetry Monitoring,” Innovative Applications of Artificial
Intelligence, 1989, AAAI Press/The MIT Press, Menlo Press, Schoor, Herbert, and Rappaport,
Alain ed.
Nash, J. “Expert Systems: A New Partnership,” AI Expert, December 1992.
Norton, J. E., et al. “Microcomputer Intelligence for Technical Training (MITT): The Evolution
of an Intelligent Tutoring System,” Proceedings of Contributed Sessions 1991 Conference on
Intelligent Computer Aided Training, Houston, TX, November 1991.
Proceedings of the First CLIPS Conference, Houston, Texas, August 1990.
Proceedings of the Second CLIPS Conference, Houston, Texas, September 1991.
Proceedings of the Third CLIPS Conference, Houston, Texas, September 1994.
Robey, B., et al. “The DRAIR Advisor: A Knowledge–Based System for Materiel Deficiency
Analysis,” Proceedings of the Fifth Innovative Applications of Artificial Intelligence Conference,
July 11–15, 1993, Washington, D.C.
Robey, B., et al. “DRAIR Advisor: A Knowledge-Based System for Materiel-Deficiency
Analysis,” AI magazine, Volume 15, No. 2, Summer, 1994.
CLIPS Reference Manual
404
Appendix I: Bibliography of CLIPS Publications
Rolincik, M, et al. “An On–line Expert System for Diagnosing Environmentally Induced
Spacecraft Anomalies using CLIPS,” Proceedings of The Sixth Annual Workshop on Space
Operations Applications and Research (SOAR ’92), Houston, TX, August 1992.
Rolincik, M., et al. “An Expert System for Diagnosing Environmentally Induced Spacecraft
Anomolies,” Proceedings of The Fifth Annual Workshop on Space Operations Applications and
Research (SOAR ’91), Houston, TX, July 1991.
Saito, T., et al. “Acquiring Knowledge within an ICAT (Intelligent Computer–Aided Training)
Environment: Factors and Issues,” Proceedings of Contributed Sessions 1991 Conference on
Intelligent Computer Aided Training, Houston, TX, November 1991.
Saito, T., et al. “On the Acquisition and Representation of Procedural Knowledge,” Proceedings
of The Fifth Annual Workshop on Space Operations Applications and Research (SOAR ’91),
Houston, TX, July 1991.
Scholtz, T. “The State Transition Diagram with Path Priority and it’s Applications,” M.S. Thesis,
Naval Postgraduate School, Monterey, CA, September 1993.
Schultz, R. D, and Stobie, I. “The AI Bus Architecture for Distributed Knowledge–Based
Systems,” Proceedings of The Fourth Annual Workshop on Space Operations Applications and
Research (SOAR ’90), Albuquerque, NM, June 1990.
Spelt, P. F. “Learning by an Autonomous Robot at a Process Control Panel,” IEEE Expert,
Winter 1989.
Spinoff 1993, NASA, pp. 88, 102, 120–121, 1994.
Spinoff 1992, NASA, p. 121, 1993.
Spinoff 1991, NASA, pp. 110–111, 1992.
Swartz, M., et al. “Intelligent Help for Radar Maintenance Troubleshooters,” Proceedings of
Contributed Sessions 1991 Conference on Intelligent Computer Aided Training, Houston, TX,
November 1991.
Szatkowski, G. P., and Levin, B. E. “Expert System Decision Support for Low–cost Launch
Vehicle Operations,” Proceedings of The Fourth Annual Workshop on Space Operations
Applications and Research (SOAR ’90), Albuquerque, NM, June 1990.
Truszkowski, W. “Advances in Knowledge–Based Software Engineering,” Proceedings of the
Technology 2001Conference, San Jose, CA, December 1991.
Wallfesh, S. K. “Infantry Load Planning with LES,” Artificial Intelligence Applications for
Logistics, Aerospace Systems, Robotics & Personnel, American Defense Preparedness
Association, WIlliamsburg, VA, 8–10 March 1993.
CLIPS Reference Manual
CLIPS Basic Programming Guide
405
Wang, L., and Bochsler, D. “Space Shuttle Onboard Navigation Console Expert/Trainer
System,” Proceedings of The First Annual Workshop on Space Operations Automation and
Robotics (SOAR ’87), Houston, TX, August 1987.
Warren, K. C., and Goodman, B. A. “Engineering Intelligent Tutoring Systems,” Proceedings of
The Contributed Sessions 1993 Conference on Intelligent Computer Aided Training and Virtual
Environment Technology (ICAT-VET ’93), Houston, TX, May 1993.
Wiederholt, B. J. “MITT Writer: An Authoring System for Developing Intelligent Tutors for
Complex Technical Domains,” Proceedings of Contributed Sessions 1991 Conference on
Intelligent Computer Aided Training, Houston, TX, November 1991.
Woods, D. “Space Station Freedom: Embedding AI,” AI Expert, April 1992.
Enhancements/Implementation
Donnell, B., “Object/rule Integration in CLIPS,” Expert Systems: The International Journal of
Knowledge Engineering and Neural Networks, Learned Information, New Jersey, February
1994, Vol. 11, No. 1, ISSN 0266-4720, pp. 29-45.
Franke, J. L., et al. “A General Purpose Certainty Processing Extension to CLIPS,” Proceedings
of The 7th Florida Artificial Intelligence Research Symposium, Florida AI Research Society,
1994.
Le, T., and Homeier, P. “Portable Inference Engine: An Extended CLIPS for Real–Time
Production Systems,” Proceedings of The Second Annual Workshop on Space Operations
Automation and Robotics (SOAR ’88), Albuquerque, NM, July 1988.
Li, Y. P. “DCLIPS—A Distributed CLIPS Implementation,” Proceedings of the 9th AIAA
Computing in Aerospace Conference, American Institute of Aeronautics and Astronautics, San
Diego, CA, October 1993.
Odette, L. L., Intelligent Embedded Systems, Addison–Wesley Publishing Company, pp. 63–
110, 1991.
Riley, G. “Implementing CLIPS on a Parallel Computer,” Proceedings of The First Annual
Workshop on Space Operations Automation and Robotics (SOAR ’87), Houston, TX, August
1987.
Riley, G. “Implementation of an Expert System Shell on a Parallel Computer,” Proceedings of
The Third Annual Artificial Intelligence & Advanced Computer Technology Conference, Long
Beach Convention Center, Long Beach, CA, April 1987.
CLIPS Reference Manual
406
Appendix I: Bibliography of CLIPS Publications
Salzgeber, M. J., et al. “Managing Uncertainty in CLIPS: A System Level Approach,”
Proceedings of The 6th Florida Artificial Intelligence Research Symposium, Florida AI Research
Society, 1993.
Eick, C. F., et al. “DALI—A Knowledge Base Management System,” Proceedings of the 1st
Conference on Industrial and Engineering Applications of AI & Expert Systems.
Rete Pattern Matching Algorithm
Forgy, C. “Rete: A Fast Algorithm for the Many Pattern/Many Object Pattern Match Problem,”
Artificial Intelligence, 19, pp. 17–37, 1982.
Forgy, C. “On the Efficient Implementation of Production Systems,” Ph. D. Thesis,
Carnegie-Mellon University, 1979.
Schneier, B. “The Rete Matching Algorithm,” AI Expert, pp. 24-29, December 1992.
CLIPS Reference Manual
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Index
- ................................................................ 190
: .................................................................. 44
? ................................................................... 7
?DERIVE ................................................... 22
?NONE ...................................................... 22
?self .................................................. 109, 110
( .................................................................... 7
) .................................................................... 7
* ............................................................... 190
** ............................................................. 197
/ ................................................................ 191
& ............................................................ 7, 41
+ ............................................................... 189
< ........................................................... 7, 164
<= ............................................................. 165
<> ............................................................. 163
= ......................................................... 46, 162
=> ............................................................... 27
> ............................................................... 163
>= ............................................................. 164
| .............................................................. 7, 41
~ ............................................................. 7, 41
$? ................................................................. 7
abs ............................................................ 192
abstraction .................................................. 18
action ........................................... 16, 27, 159
activated ..................................................... 28
active-duplicate-instance ........... 83, 115, 130
active-initialize-instance .................... 83, 124
active-make-instance ................. 83, 121, 123
active-message-duplicate-instance ... 83, 115,
132
active-message-modify-instance 83, 115, 129
active-modify-instance .............. 83, 114, 128
Ada ......................................... iv, 8, 9, 15, 16
Advanced Programming Guide .. v, 1, 3, 5, 8,
51, 161, 178, 194, 309
agenda .............. 28, 29, 33, 62, 289, 290, 291
allowed-classes ........................................ 154
allowed-instance-names .......................... 155
allowed-instances .................................... 155
ampersand .................................................... 7
and ........................................................... 165
antecedent .................................................. 15
any-factp .......................................... 230, 324
any-instancep ..................................... 83, 139
apropos .................................................... 275
arrow .......................................................... 27
ART ........................................................... iii
Artificial Intelligence Section .................... iii
assert .............. 11, 22, 83, 211, 217, 220, 266
assert-string .............................................. 220
attribute
default .................................................. 22
auto-focus .................................................. 63
backslash ...................... 7, 180, 185, 186, 220
Basic Programming Guide ................. iv, v, 1
batch ................................................ 3, 5, 272
batch* .................................................. 5, 272
bind ........................ 39, 65, 83, 110, 126, 199
bload ........................................ 270, 271, 274
bload-instances ................................ 307, 308
break .......................... 83, 139, 202, 204, 230
browse-classes ......................................... 302
bsave ........................................ 153, 270, 271
bsave-instances ................................ 307, 308
build ................................................. 175, 326
C ................................ iii, 8, 9, 12, 15, 16, 21
call-next-handler ................ 83, 117, 118, 255
call-next-method .................. 83, 86, 241, 242
call-specific-method .............. 75, 83, 86, 242
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Index
carriage return .............................................. 7
case sensitive ............................................... 7
check-syntax ............................................ 177
class ......................... 8, 13, 78, 258, 299, 302
abstract ........................... 90, 95, 253, 299
concrete .................................. 91, 95, 253
existence ............................................ 245
immediate .................................... 95, 107
non-reactive ......................................... 95
precedence ........................................... 93
reactive .................................. 91, 95, 253
specific ........................... 92, 95, 100, 118
system .................................................. 89
ADDRESS ..................................... 89
EXTERNAL-ADDRESS .............. 89
FACT-ADDRESS ......................... 89
FLOAT .......................................... 89
INITIAL-OBJECT ........................ 89
INSTANCE ................................... 89
INSTANCE-ADDRESS ................ 89
INSTANCE-NAME ...................... 89
INTEGER ...................................... 89
LEXEME ....................................... 89
MULTIFIELD ............................... 89
NUMBER ...................................... 89
OBJECT .......................... 89, 92, 302
PRIMITIVE ................................... 89
STRING ......................................... 89
SYMBOL ...................................... 89
USER ....... 89, 92, 112, 124, 257, 306
user-defined ............................. 8, 14, 306
class function ................................... 240, 258
class-abstractp .......................................... 247
class-existp .............................................. 245
class-reactivep ......................................... 247
class-slots ................................................. 248
class-subclasses ....................................... 248
class-superclasses .................................... 247
clear 11, 25, 65, 123, 145, 147, 151, 270, 271
clear-focus-stack ...................................... 292
CLIPS ........................................................ iii
CLOS ................................................... 75, 89
close ......................................................... 180
command ..................................... 3, 159, 269
command prompt ......................................... 3
comment ................................................ 7, 10
Common Lisp Object System ..................... iv
condition .................................................... 16
conditional element ........... 16, 25, 27, 33, 62
and ........................................... 27, 33, 53
exists .............................................. 33, 55
forall .............................................. 33, 56
logical ............................................ 33, 58
not .................................................. 33, 54
or .................................................... 33, 52
pattern ...................................... 27, 33, 34
literal .............................................. 35
test ............................................ 30, 33, 51
conflict resolution strategy ... 16, 28, 29, 271,
272, 291
breadth ................................................. 29
complexity ........................................... 30
depth .................................................... 29
lex ........................................................ 30
mea ...................................................... 31
random ................................................. 32
simplicity ............................................. 29
consequent ................................................. 15
conservation ............................................. 253
conserve-mem .................................. 270, 310
constant .................................................... 3, 9
constraint ................................. 33, 34, 41, 44
connective ...................................... 34, 41
field ...................................................... 34
literal .................................................... 35
predicate .................................. 34, 44, 51
return value .................................... 34, 46
construct ........................................ 3, 10, 175
constructs ................................................. 316
constructs-to-c ......................... 274, 324, 325
convenience ............................................. 253
COOL .. iv, 8, 14, 17, 18, 19, 75, 78, 89, 240,
244, 298
create$ ...................................................... 166
crlf ............................................................ 181
daemon .................................... 111, 121, 137
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deactivated ................................................. 28
declarative technique ................. 86, 107, 118
declare ........................................................ 62
default-dynamic ......................................... 22
defclass ............................ 8, 10, 91, 105, 298
defclass-module ....................................... 244
deffacts .................................. 10, 13, 25, 283
deffacts-module ....................................... 234
deffunction ........... 9, 10, 16, 71, 75, 294, 295
action ................................................... 72
advantages over generic functions ..... 341
execution error ..................................... 72
recursion .............................................. 72
regular parameter ................................. 71
return value .......................................... 72
wildcard parameter .............................. 71
deffunction-module ................................. 238
defgeneric ...................................... 10, 75, 76
defgeneric-module ................................... 239
defglobal ................................ 10, 15, 65, 293
defglobal-module ..................................... 238
definstances ................... 10, 15, 91, 122, 305
initial-object ......................................... 91
definstances-module ................................ 256
defmessage-handler ........... 10, 105, 106, 303
defmethod ...................................... 10, 75, 76
defmodule .......................... 10, 145, 308, 309
defmodules ................................................ 17
defrule .......................................... 10, 27, 283
defrule-module ........................................ 235
deftemplate ............................ 10, 12, 21, 279
deftemplate fact ........................... 12, 21, 220
deftemplate-module ................................. 212
deftemplate-slot-allowed-values ...... 212, 322
deftemplate-slot-cardinality ............. 212, 322
deftemplate-slot-defaultp ................. 213, 322
deftemplate-slot-default-value ......... 214, 322
deftemplate-slot-existp .................... 214, 322
deftemplate-slot-multip ................... 215, 322
deftemplate-slot-names .................... 215, 322
deftemplate-slot-range ..................... 216, 322
deftemplate-slot-singlep .................. 216, 323
deftemplate-slot-type ............................... 323
deftemplate-slot-types ............................. 216
deg-grad ................................................... 195
deg-rad ..................................................... 195
delayed-do-for-all-facts ........... 230, 233, 324
delayed-do-for-all-instances ..... 83, 139, 142,
204, 327
delete$ ...................................................... 168
delete-instance ................................. 126, 257
delete-member$ ....................................... 172
delimiter ....................................................... 7
dependencies ............................................ 289
dependents ............................................... 289
describe-class ..................................... 92, 299
direct-insert$ ............................................ 262
div ............................................................ 191
do-for-all-facts ................. 230, 232, 233, 324
do-for-all-instances ... 83, 139, 141, 142, 204,
327
do-for-fact ................................ 230, 232, 324
do-for-instance ........... 83, 139, 141, 204, 327
double quote ................................................ 7
dribble-off ................................................ 276
dribble-on ................................................ 275
duplicate .................. 11, 13, 23, 83, 220, 266
duplicate-instance ...................... 83, 115, 130
dynamic binding ........................................ 18
dynamic-get ............................. 125, 260, 371
dynamic-put ............................. 125, 261, 371
embedded application .................................. 5
encapsulation ....................... 18, 89, 109, 120
EnvFalseSymbol ...................................... 325
EnvTrueSymbol ....................................... 325
EOF .......................................... 182, 183, 187
eq ............................................................. 161
eval .................................................. 175, 326
evenp ........................................................ 160
exit ............................................... 4, 180, 271
exp ........................................................... 197
expand$ .............................. 83, 108, 266, 325
explode$ .................................................. 168
exponential notation .................................... 6
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Index
exporting constructs ................................. 147
expression .................................................. 10
external-address ........................... 6, 8, 9, 181
-f .................................................................. 4
-f2 ................................................................ 5
facet ............................................. 91, 96, 299
access
initialize-only ................................. 98
read-only ........................................ 98
read-write ....................................... 98
create-accessor ................... 103, 253, 326
?NONE ........................................ 103
read .............................................. 103
read-write ..................................... 103
write ............................................. 103
default .................................................. 96
default-dynamic ................................... 96
multislot ............................................... 96
override-message ............................... 104
pattern-match
non-reactive ................................. 101
reactive ........................................ 101
propagation
inherit ............................................. 99
no-inherit ................................. 95, 99
shared ................................................... 96
single-slot ............................................ 96
slot ....................................................... 96
source
composite ............................... 95, 100
exclusive ...................................... 100
storage
local ............................................... 97
shared ............................................. 97
visibility ............................................. 102
private .......................................... 102
public ........................................... 102
fact ......................................... 11, 13, 25, 280
fact identifier ............................................. 11
fact-address .............. 6, 8, 9, 11, 50, 181, 227
fact-existp ................................................ 222
fact-index ..... 11, 23, 218, 219, 220, 221, 289
fact-list ..................................... 11, 13, 25, 27
fact-relation .............................................. 222
facts .......................................................... 280
fact-set ..................................................... 226
action ................................................. 229
distributed action ............................... 229
member .............................................. 226
member variable ........................ 226, 229
query .......................................... 228, 229
query execution error ......................... 230
query functions .................................. 230
template ............................................. 226
template restriction ............................ 226
fact-slot-names ........................................ 222
fact-slot-value .......................................... 223
FALSE ....................................................... 44
FalseSymbol ............................................ 325
fetch ................................................. 312, 324
ff .............................................................. 181
field ........................................................ 9, 12
find-all-facts ............................ 231, 233, 324
find-all-instances ....................... 83, 140, 142
find-fact ........................................... 231, 324
find-instance ...................................... 83, 140
fire .............................................................. 27
first$ ......................................................... 171
float .................................................. 6, 8, 193
floatp ........................................................ 159
focus .................................... 28, 63, 151, 291
foreach ....................... 83, 204, 206, 266, 322
format ...................................... 183, 188, 323
FORTRAN .................................................. 9
funcall .............................. 211, 324, 325, 327
function ................ 3, 9, 16, 75, 138, 159, 229
call ................................................... 3, 10
external ................................ 5, 39, 46, 51
predicate ........................ 44, 51, 159, 259
reserved names .................................. 393
system defined ............................... 9, 393
user defined ......................... 8, 9, 51, 378
generic dispatch ............... 75, 76, 79, 81, 341
generic function ............... 14, 16, 17, 75, 295
disadvantages ..................................... 341
header ............................................ 76, 77
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order dependence ................................. 76
ordering of method parameter
restrictions ......................................... 341
performance penalty ............................ 76
return value .......................................... 87
gensym ............................................. 207, 208
gensym* ........................... 121, 129, 207, 208
get-auto-float-dividend ............................ 274
get-char ............................................ 186, 323
get-class-defaults-mode ................... 253, 327
get-current-module .................................. 263
get-defclass-list ........................................ 244
get-deffacts-list ........................................ 234
get-deffunction-list .................................. 238
get-defgeneric-list .................................... 239
get-defglobal-list ...................................... 237
GetDefglobalValue .................................. 325
get-definstances-list ................................. 256
get-defmessage-handler-list ..................... 248
get-defmethod-list .................................... 239
get-defmodule-list .................................... 263
get-defrule-list ......................................... 235
get-deftemplate-list .................................. 217
get-dynamic-constraint-checking ............ 274
get-fact-duplication .................................. 282
get-fact-list ............................................... 224
get-focus .................................................. 236
get-focus-stack ......................................... 236
get-function-restrictions .................... 83, 210
get-incremental-reset ............................... 288
get-method-restrictions ...................... 83, 243
GetNextFactInTemplate .......................... 324
get-profile-percent-threshold ................... 315
get-region ......................................... 314, 323
get-reset-globals ...................................... 294
get-salience-evaluation ............................ 292
get-sequence-operator-recognition .......... 267
get-static-constraint-checking .................. 275
get-strategy .............................................. 291
grad-deg ................................................... 195
halt ........................................................... 291
help .......................................................... 322
help-path .................................................. 322
I/O router ................................................. 178
if ................................................. 83, 200, 266
if portion .................................................... 15
imperative technique ................. 86, 107, 118
implode$ .................................................. 169
importing constructs ................................ 147
incremental reset ........................ 28, 272, 288
Inference Corporation ................................ iii
inference engine ............................. 16, 27, 28
inheritance ............................... 14, 18, 91, 95
class precedence list ... 19, 91, 92, 93, 95,
100, 118, 299
class precedence list .......................... 106
is-a ....................................................... 92
multiple ................ 14, 19, 89, 92, 93, 302
initialize-instance . 83, 97, 104, 112, 124, 257
init-slots ........................... 112, 121, 124, 257
insert$ ...................................................... 170
instance .......... 8, 13, 14, 15, 95, 97, 299, 306
active . 109, 116, 118, 125, 126, 257, 260,
306
creation ...................................... 116, 120
deletion .............................................. 113
direct .................................. 90, 91, 95, 99
initialization ............... 112, 120, 124, 257
manipulation ...................................... 120
printing .............................................. 113
instance-address .... 6, 8, 9, 50, 181, 258, 259,
341
instance-addressp ..................................... 260
instance-existp ......................................... 260
instance-list .......................................... 15, 27
instance-name .......... 6, 8, 135, 258, 259, 260
instance-namep ........................................ 260
instance-name-to-symbol ........................ 259
instancep .................................................. 259
instances .................................................. 306
instance-set .............................................. 135
action ................................................. 138
class restriction .................................. 135
distributed action ............................... 137
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member .............................................. 135
member variable ........................ 135, 138
query ............................ 19, 137, 138, 341
query execution error ......................... 139
query functions .................................. 139
template ............................................. 135
integer .............................................. 6, 8, 193
integerp .................................................... 159
integration .................................................... 5
Interfaces Guide ....................................... v, 3
Jess ........................................................... 207
-l ................................................................... 5
left-hand side ............................................. 15
length ....................................................... 209
length$ ............................... 96, 108, 172, 209
less than ....................................................... 7
lexemep .................................................... 160
LHS ............................................................ 27
line feed ....................................................... 7
LISP ..................................................... iii, 15
list-defclasses ........................................... 298
list-deffacts .............................................. 283
list-deffunctions ....................................... 295
list-defgenerics ........................................ 296
list-defglobals .......................................... 293
list-definstances ....................................... 305
list-defmessage-handlers ......................... 303
list-defmethods .............. 77, 83, 84, 296, 297
list-defmodules ........................................ 309
list-defrules .............................................. 284
list-deftemplates ...................................... 279
list-focus-stack ......................................... 292
list-watch-items ....................................... 278
load ...................................... 5, 269, 270, 272
load* ........................................................ 269
load-facts ................................................. 280
LoadFactsFromString .............................. 326
load-instances .......................................... 308
local ......................................................... 281
log ............................................................ 197
log10 ........................................................ 198
logical name ..................................... 179, 275
nil ............................................... 181, 183
stdin ................... 182, 183, 186, 187, 275
stdout ................................. 181, 183, 275
t .......................... 181, 182, 183, 186, 187
wclips ................................................. 275
wdialog .............................................. 275
wdisplay ............................................. 275
werror ................................................ 275
wtrace ................................................ 275
wwarning ........................................... 275
logical support ................... 58, 218, 219, 289
loop-for-count .................... 83, 202, 204, 266
lowcase .................................................... 176
make-instance ....... 8, 48, 83, 95, 97, 99, 104,
112, 120, 122, 257, 308
matches .................................................... 285
math functions ................................. 189, 194
max .......................................................... 192
max-number-of-elements ........................ 156
member$ .......................................... 167, 326
mem-requests ........................................... 309
mem-used ................................................ 309
message ... 14, 16, 17, 18, 19, 75, 89, 97, 106,
108, 109, 116, 118, 120, 121, 124
dispatch .............................................. 107
execution error ................... 108, 118, 254
execution error ................................... 119
implementation .......................... 106, 107
return value ........................................ 120
message dispatch ..................................... 116
message-duplicate-instance83, 104, 115, 131
message-handler ... 14, 16, 17, 19, 76, 89, 91,
92, 99, 106, 109, 118, 120, 125, 199, 257,
299, 306, 341
action ................................................. 109
applicability ....... 107, 108, 116, 118, 304
documentation ................................... 105
existence ............................................ 246
forward declaration ............................ 105
regular parameter ............................... 108
return value ........................................ 120
shadow ....................................... 118, 254
specific ............................... 116, 118, 120
system
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create .................... 116, 120, 121, 326
delete ............ 113, 121, 122, 126, 129
direct-duplicate .................... 115, 130
direct-modify ............... 114, 127, 128
init .......... 99, 112, 120, 121, 124, 256
message-duplicate ........ 115, 131, 132
message-modify ........... 115, 128, 129
print .............................................. 113
type
after .............................. 106, 118, 120
around .................. 106, 118, 120, 254
before ........................... 106, 118, 120
primary ........................ 106, 118, 120
wildcard parameter ............................ 108
message-handler-existp ........................... 246
message-modify-instance .. 83, 104, 115, 128
method ..................................... 17, 75, 76, 89
action ................................................... 76
applicability ........................... 79, 86, 297
execution error ............................. 86, 240
explicit ..................................... 75, 79, 82
implicit ..................................... 75, 76, 79
index ............................................ 77, 296
parameter query restriction .................. 78
parameter restriction .... 76, 77, 78, 82, 84
parameter type restriction .................... 78
precedence ....................... 78, 79, 84, 296
regular parameter ........................... 78, 79
return value .......................................... 87
shadow ................................. 86, 240, 304
wildcard parameter .............................. 79
wildcard parameter restriction ............. 76
min ........................................................... 192
min-number-of-elements ......................... 156
mod .......................................................... 198
modify ...................... 11, 13, 23, 83, 219, 266
modify-instance ......................... 83, 114, 127
module specifier ...................................... 147
multifield value ........................................ 8, 9
multifield wildcard .................................... 36
multifieldp ............................................... 161
named fields ............................................... 12
NASA ........................................................ iii
neq ........................................................... 162
next-handlerp ..................................... 83, 254
next-methodp ..................................... 83, 240
non-FALSE ................................................ 44
non-ordered fact ................................... 12, 21
not ............................................................ 166
nth$ .................................................... 96, 166
numberp ................................................... 159
object ......................................... 8, 13, 17, 18
behavior . 13, 16, 17, 18, 75, 91, 106, 107
primitive type ....................................... 14
properties ..................... 13, 14, 17, 18, 91
reference .................................... 8, 13, 19
object-pattern-match-delay .. 48, 83, 126, 266
oddp ......................................................... 161
off ............................................................ 316
open ................................................. 179, 180
operating-system .............................. 211, 322
OPS5 .......................................................... 30
options ..................................................... 273
or .............................................................. 165
ordered fact .......................................... 12, 21
overload ..................... 10, 17, 71, 75, 76, 341
override-next-handler ........ 83, 117, 118, 255
override-next-method .......... 83, 86, 241, 242
parenthesis ............................................. 7, 10
Pascal ............................................. 12, 16, 21
pattern .................................................. 16, 27
pattern entity .............................................. 27
pattern-address ........................................... 50
pattern-matching ............................ 16, 65, 66
performance ............................................. 339
pi .............................................................. 196
pointerp .................................................... 161
polymorphism ............................................ 18
pop-focus ................................................. 237
ppdefclass ................................................ 298
ppdeffacts ................................................ 283
ppdeffunction ........................................... 295
ppdefgeneric ............................................ 295
ppdefglobal .............................................. 293
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ppdefinstances ......................................... 305
ppdefmessage-handler ............................. 303
ppdefmethod ............................................ 296
ppdefmodule ............................................ 309
ppdefrule .................................. 147, 271, 284
ppdeftemplate .......................................... 279
ppfact ............................................... 282, 323
ppinstance ................................................ 306
pprule ....................................................... 284
prefix notation ........................................... 10
preview-generic ....................................... 297
preview-send ............................................ 304
printout .................................... 181, 183, 327
print-region .............................................. 313
profile ...................................................... 316
profile-info ....................................... 315, 316
profile-reset .............................................. 315
progn .. 83, 126, 138, 203, 204, 266, 316, 327
progn$ ................ 83, 203, 204, 207, 266, 326
quote ............................................................ 7
rad-deg ..................................................... 196
random ............................................. 208, 327
read .................................. 178, 182, 183, 272
readline ............................................ 182, 272
read-number ............................. 187, 188, 323
Reference Manual ................................. v, vii
refresh ...................................................... 288
refresh-agenda ......................................... 292
release-mem ............................................. 310
remove ..................................................... 186
remove-break ........................................... 287
rename ..................................................... 185
replace$ .................................................... 170
replace-member$ ..................................... 172
reset ..... 11, 13, 15, 25, 65, 91, 120, 122, 151,
159, 271, 272, 283, 294
rest$ ......................................................... 171
restore-instances ...................................... 308
RETE algorithm ....................................... 339
retract ........................................... 11, 50, 218
return .... 28, 83, 139, 151, 202, 204, 230, 266
RHS ........................................................... 27
right-hand side ........................................... 15
round ........................................................ 198
roundoff ....................................................... 6
RtnArgCount ........................................... 326
rule ....................................................... 15, 27
run ............................................ 151, 290, 291
salience .................................. 28, 29, 62, 292
dynamic ................................. 28, 63, 292
save .......................................... 270, 310, 326
save-facts ................................................. 281
save-instances .................................. 307, 308
scientific math functions .......................... 194
seed .................................................... 33, 209
semicolon ............................................... 7, 10
send ...... 17, 19, 106, 116, 119, 120, 304, 341
sequence expansion ................................... 39
sequencep ................................................ 161
set-auto-float-dividend .................... 191, 274
set-break .................................................. 287
set-class-defaults-mode ........... 253, 326, 327
set-current-module ................... 147, 263, 290
set-dynamic-constraint-checking ...... 23, 105,
153, 271, 274
set-fact-duplication .................................. 281
setgen ....................................................... 208
set-incremental-reset ................................ 288
set-locale .................................. 187, 188, 323
set-profile-percent-threshold ................... 315
set-reset-globals ................................. 65, 294
set-salience-evaluation ...................... 63, 292
set-sequence-operator-recognition .......... 267
set-static-constraint-checking ... 23, 105, 153,
274
set-strategy ................................. 29, 159, 291
show-breaks ............................................. 288
show-defglobals ....................................... 294
significant digits .......................................... 6
single-field value ......................................... 9
single-field wildcard .................................. 36
slot 12, 14, 19, 91, 92, 95, 100, 120, 245, 299
access ........................... 98, 103, 245, 246
accessor ...................................... 103, 137
put-<slot-name> .......................... 121
default value .. 96, 97, 121, 124, 257, 307
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direct access ............... 110, 125, 137, 199
existence ............................................ 245
facet ............................................. 96, 100
inheritance propagation ....................... 99
multifield ........................................... 261
overlay ............................................... 100
override ................................................ 99
visibility ............................................. 246
slot daemons ............................................ 341
slot-allowed-classes ......................... 254, 323
slot-allowed-values .................................. 251
slot-cardinality ......................................... 251
slot-default-value ..................................... 252
slot-delete$ .............................................. 262
slot-direct-accessp ................................... 246
slot-direct-delete$ .................................... 262
slot-direct-replace$ .................................. 261
slot-existp ................................................ 245
slot-facets ................................................. 249
slot-initablep ............................................ 246
slot-insert$ ......................................... 96, 262
slot-override ..................... 121, 124, 257, 307
slot-publicp .............................................. 246
slot-range ................................................. 252
slot-replace$ ............................................ 261
slot-sources .............................................. 250
slot-types .................................................. 250
slot-writablep ................................... 246, 325
Smalltalk ......................................... iv, 75, 89
sort ................................................... 210, 327
space ............................................................ 7
specificity .................................................. 29
sqrt ........................................................... 196
standard math functions ........................... 189
str-cat ....................................................... 173
str-compare .............................................. 176
str-index ................................................... 174
string .................................................... 6, 7, 8
stringp ...................................................... 160
string-to-field ................................... 178, 327
str-length .................................................. 177
subclass ...................... 92, 116, 245, 299, 302
subclassp .................................................. 245
subseq$ .................................................... 169
subsetp ..................................................... 167
sub-string ................................................. 174
superclass ............... 91, 92, 95, 106, 245, 299
direct .................................................... 92
superclassp ............................................... 245
switch ................................. 83, 205, 266, 327
symbol ................................. 6, 7, 8, 258, 259
reserved ................................................ 12
and ................................................. 12
declare ............................................ 12
exists .............................................. 12
forall .............................................. 12
logical ............................................ 12
not .................................................. 12
object ............................................. 12
or .................................................... 12
test .................................................. 12
symbolp ................................................... 160
symbol-to-instance-name ........................ 259
sym-cat .................................................... 173
system ...................................................... 273
tab ........................................................ 7, 181
template ................................................... 219
then portion ................................................ 15
tilde .............................................................. 7
time .......................................................... 209
timer ......................................................... 211
timer ......................................................... 327
top level ....................................................... 3
toss ........................................................... 315
trigonometric math functions .................. 194
TrueSymbol ............................................. 325
truth maintenance ...................................... 58
type function .................................... 240, 258
unconditional support ................................ 58
undefclass ................................................ 298
undeffacts ................................................ 283
undeffunction ........................................... 295
undefgeneric ............................................ 296
undefglobal ........................................ 65, 293
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Index
undefinstances ......................................... 306
undefmessage-handler ............................. 304
undefmethod ............................................ 297
undefrule .......................................... 147, 284
undeftemplate .......................................... 279
unmake-instance ................................ 50, 257
unwatch .................................................... 278
upcase ...................................................... 176
User’s Guide ......................................... v, vii
user-functions .......................................... 316
value ............................................................ 9
variable ... 5, 7, 9, 11, 15, 34, 35, 38, 54, 175,
199
global ................... 3, 15, 62, 65, 199, 271
vertical bar ................................................... 7
visible ...................................................... 281
vtab .......................................................... 181
watch ................................................ 276, 278
watch item
activations .................................... 28, 277
all ....................................................... 277
compilations .............................. 269, 276
deffunctions ....................................... 277
facts .................................... 217, 218, 276
focus .................................................. 277
generic-functions ............................... 277
globals .......................................... 65, 277
instances ............................................ 277
message-handlers ............................... 277
messages ............................................ 277
methods .............................................. 277
rules ........................................... 277, 290
slots .................................................... 277
statistics ..................................... 277, 290
while .......................................... 83, 201, 266
wildcard ......................................... 34, 35, 36
wordp ....................................................... 160
