The Compiler Generator Coco/R User Manual

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The Compiler Generator Coco/R
User Manual
Hanspeter Mössenböck
Johannes Kepler University Linz
Institute of System Software

Coco/R 1 is a compiler generator, which takes an attributed grammar of a source language
and generates a scanner and a parser for this language. The scanner works as a
deterministic finite automaton. The parser uses recursive descent. LL(1) conflicts can be
resolved by a multi-symbol lookahead or by semantic checks. Thus the class of accepted
grammars is LL(k) for an arbitrary k.
There are versions of Coco/R for C#, Java, C++, Delphi, Modula-2, Oberon and other
languages. This manual describes the versions for C#, Java and C++ from the University
of Linz.
Download from: http://ssw.jku.at/Coco/

Compiler Generator Coco/R,
Copyright © 1990, 2010 Hanspeter Mössenböck, University of Linz
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public
License as published by the Free Software Foundation; either version 2, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the
implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License along with this program; if not, write to the
Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
As an exception, it is allowed to write an extension of Coco/R that is used as a plugin in non-free software.
If not otherwise stated, any source code generated by Coco/R (other than Coco/R itself) does not fall under the
GNU General Public License.
1

Coco/R stands for compiler compiler generating recursive descent parsers.

2

Contents
1. Overview ..............................................................................................................................................3
1.1 Sample Production.........................................................................................................................3
1.2 Sample Parsing Method .................................................................................................................4
1.3 Summary of Features.....................................................................................................................4
2. Input Language.....................................................................................................................................5
2.1 Vocabulary.....................................................................................................................................5
2.2 Overall Structure............................................................................................................................6
2.3 Scanner Specification ....................................................................................................................7
2.3.1 Character sets .........................................................................................................................7
2.3.2 Tokens....................................................................................................................................8
2.3.3 Pragmas..................................................................................................................................9
2.3.4 Comments ............................................................................................................................10
2.3.5 White space..........................................................................................................................10
2.3.6 Case sensitivity ....................................................................................................................11
2.4 Parser Specification .....................................................................................................................11
2.4.1 Productions ..........................................................................................................................11
2.4.2 Semantic Actions .................................................................................................................12
2.4.3 Attributes .............................................................................................................................12
2.4.4 The Symbol ANY ................................................................................................................14
2.4.5 LL(1) Conflicts ....................................................................................................................14
2.4.6 LL(1) Conflict Resolvers .....................................................................................................17
2.4.7 Syntax Error Handling .........................................................................................................20
2.4.8 Frame Files...........................................................................................................................23
3. User Guide..........................................................................................................................................23
3.1 Installation ...................................................................................................................................23
3.2 Options.........................................................................................................................................23
3.3 Invocation ....................................................................................................................................24
3.4 Interfaces of the Generated Classes .............................................................................................25
3.4.1 Scanner.................................................................................................................................25
3.4.2 Token ...................................................................................................................................25
3.4.3 Buffer ...................................................................................................................................25
3.4.4 Parser ...................................................................................................................................26
3.4.5 Errors ...................................................................................................................................26
3.5 Main Class of the Compiler .........................................................................................................27
3.6 Grammar Tests.............................................................................................................................28
4. A Sample Compiler ............................................................................................................................30
5. Applications of Coco/R ......................................................................................................................32
6. Acknowledgements ............................................................................................................................33
A. Syntax of Cocol/R .............................................................................................................................34
B. Sources of the Sample Compiler........................................................................................................35
B.1 Taste.ATG....................................................................................................................................35
B.2 SymTab.cs (symbol table)...........................................................................................................38
B.3 CodeGen.cs (code generator) ......................................................................................................40
B.4 Taste.cs (main program)..............................................................................................................42

3

1. Overview
Coco/R is a compiler generator, which takes an attributed grammar of a source
language and generates a scanner and a recursive descent parser for this language. The
user has to supply a main class that calls the parser as well as semantic classes (e.g. a
symbol table handler or a code generator) that are used by semantic actions in the
parser. This is shown in Figure 1.
Main
Parser

Coco/R
compiler
description

Scanner
semantic classes

Figure 1 Input and output of Coco/R

1.1 Sample Production
In order to give you an idea of how attributed grammars look like in Coco/R, let us
look at a sample production for variable declarations in a Pascal-like language:
VarDeclaration
= Ident
{ ',' Ident

}
':' Type

(. string name; TypeDesc type; .)
(. Obj x = symTab.Enter(name);
int n = 1; .)
(. Obj y = symTab.Enter(name);
x.next = y; x = y;
n++; .)
(. adr += n * typ.size;
for (int a = adr; x != null; x = x.next) {
a -= type.size;
x.adr = a;
} .)

';' .

The core of this specification is the EBNF production
VarDeclaration = Ident {',' Ident} ':' Type ';'.

It is augmented with attributes and semantic actions. The attributes (e.g. )
specify the parameters of the symbols. There are input attributes (e.g. ) and
output attributes (e.g.  or ). A semantic action is a piece of code that
is written in the target language of Coco/R (e.g. in C#, Java or C++) and is executed
by the generated parser at its position in the production.

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1.2 Sample Parsing Method
Every production is translated into a parsing method. The method for VarDeclaration,
for example, looks like this in C# (code parts originating from attributes or semantic
actions are shown in gray):
void VarDeclaration(ref int adr) {
string name; TypeDesc type;
Ident(out name);
Obj x = symTab.Enter(name);
int n = 1;
while (la.kind == comma) {
Get();
Ident(out name);
Obj y = symTab.Enter(name);
x.next = y; x = y;
n++;
}
Expect(colon);
Type(out type);
adr += n * type.size;
for (int a = adr; x != null; x = x.next) {
a -= type.size;
x.adr = a;
}
Expect(semicolon);
}

Coco/R also generates a scanner that reads the input stream and returns a stream of
tokens to the parser.

1.3 Summary of Features
Scanner
 The scanner is specified by a list of token declarations. Literals (e.g. "if" or
"while") do not have to be declared as tokens but can be used directly in the
productions of the grammar.
 The scanner is implemented as a deterministic finite automaton (DFA). Therefore
the terminal symbols (or tokens) have to be described by a regular EBNF grammar.
 Comments may be nested. One can specify multiple kinds of comments for a
language.
 The scanner supports Unicode characters encoded in UTF-8.
 The scanner can be made case-sensitive or case-insensitive.
 The scanner can recognize tokens depending on their context in the input stream.
 The scanner can read from any input stream (not just from a file). However, all
input must come from a single stream (no includes).
 The scanner can handle so-called pragmas, which are tokens that are not part of the
syntax but can occur anywhere in the input stream (e.g. compiler directives or endof-line characters).
 The user can suppress the generation of a scanner and can provide a hand-written
scanner instead.

5

Parser
 The parser is specified by a set of EBNF productions with attributes and semantic
actions. The productions allow for alternatives, repetition and optional parts.
Coco/R translates the productions into an efficient recursive descent parser. The
parser is reentrant, so multiple instances of it can be active at the same time.
 Nonterminal symbols can have any number of input and output attributes (the Java
version allows just one output attribute, which may, however, be an object of a
suitable composite class). Terminal symbols do not have explicit attributes, but the
tokens returned by the scanner contain information that can be viewed as attributes.
All attributes are evaluated during parsing (i.e. the grammar is processed as an Lattributed grammar).
 Semantic actions can be placed anywhere in the grammar (not just at the end of
productions). They may contain arbitrary statements or declarations written in the
language of the generated parser (e.g. C#, Java or C++).
 The special symbol ANY can be used to denote a set of complementary tokens.
 In principle, the grammar must be LL(1). However, Coco/R can also handle nonLL(1) grammars by using so-called resolvers that make a parsing decision based on
a multi-symbol lookahead or on semantic information.
 Every production can have its own local variables. In addition to these, one can
declare global variables or methods, which are translated into fields and methods of
the parser. Semantic actions can also access other objects or methods from userwritten classes or from library classes.
 Coco/R checks the grammar for completeness, consistency and non-redundancy. It
also reports LL(1) conflicts.
 The error messages printed by the generated parser can be configured to conform to
a user-specific format.
 The generated parser and scanner can be specified to belong to a certain namespace
(or package).

2. Input Language
This section specifies the compiler description language Cocol/R that is used as the
input language for Coco/R. A compiler description consists of a set of grammar rules
that describe the lexical and syntactical structure of a language as well as its
translation to a target language.

2.1 Vocabulary
The basic elements of Cocol/R are identifiers, numbers, strings and character
constants, which are defined as follows:
ident
number
string
char

=
=
=
=

letter {letter | digit}.
digit {digit}.
'"' {anyButQuote} '"'.
'\'' anyButApostrophe '\''.

Upper case letters are distinct from lower case letters. Strings must not extend across
multiple lines. Both strings and character constants may contain the following escape
sequences:

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\\
\'
\"
\0

backslash
apostrophe
quote
null character

\r
\n
\t
\v

carriage return
new line
horizontal tab
vertical tab

\f
\a
\b
\uxxxx

form feed
bell
backspace
hex char value

The following identifiers are reserved keywords (in the C# version of Cocol/R the
identifier using is also a keyword, in the Java version the identifier import):
ANY
CHARACTERS
COMMENTS
COMPILER

CONTEXT
END
FROM
IF

IGNORE
IGNORECASE
NESTED
out

PRAGMAS
PRODUCTIONS
SYNC
TO

TOKENS
WEAK

Comments are enclosed in /* and */ and may be nested. Alternatively they can start
with // and go to the end of the line.
EBNF
All syntax descriptions in Cocol/R are written in Extended Backus-Naur Form
(EBNF) [Wirth77]. By convention, identifiers starting with a lower case letter denote
terminal symbols, identifiers starting with an upper case letter denote nonterminal
symbols. Strings denote themselves. The following meta-characters are used:
symbol
=
.
|
()
[]
{}

meaning
separates the sides of a production
terminates a production
separates alternatives
groups alternatives
option
iteration (0 or more times)

example
A=abc.
A=abc.
ab|c|de
(a | b) c
[a] b
{a} b

means a b or c or d e
means a c or b c
means a b or b
means b or a b or a a b or ...

Attributes are written between < and >. Semantic actions are enclosed in
The operators + and - are used to form character sets.

(.

and

.).

2.2 Overall Structure
A Cocol/R compiler description has the following structure:
Cocol =
[Imports]
"COMPILER" ident
[GlobalFieldsAndMethods]
ScannerSpecification
ParserSpecification
"END" ident '.'
.

The name after the keyword COMPILER is the grammar name and must match the name
after the keyword END. The grammar name also denotes the topmost nonterminal
symbol (the start symbol). The parser specification must contain a production for this
symbol.
Imports. In front of the keyword COMPILER one can import namespaces (in C#) or
packages (in Java) or include header files (in C++), for example:
using System;
using System.Collections;

7
GlobalFieldsAndMethods. After the grammar name one may declare arbitrary fields
and methods of the generated parser, for example:
int sum;
void Add(int x) {
sum = sum + x;
}

These declarations are written in the language of the generated parser (i.e. in C#, Java
or C++) and are not checked by Coco/R. They can be used in the semantic actions of
the parser specification. In the C++ version of Coco/R global fields and methods are
copied to the header file of the generated parser.
The remaining parts of the compiler description specify the scanner and the parser
that are to be generated. They are now described in more detail.

2.3 Scanner Specification
A scanner has to read source text, skip meaningless characters, recognize tokens and
pass them to the parser. This is described in a scanner specification, which consists of
five optional parts:
ScannerSpecification =
["IGNORECASE"]
["CHARACTERS" {SetDecl}]
["TOKENS" {TokenDecl}]
["PRAGMAS" {PragmaDecl}]
{CommentDecl}
{WhiteSpaceDecl}.

2.3.1 Character sets
This section allows the user to declare character sets such as letters or digits. Their
names can then be used in the other sections of the scanner specification. Coco/R
supports the Unicode character set (UTF-8-encoded).
SetDecl = ident '=' Set '.'.
Set
= BasicSet {('+'|'-') BasicSet}.
BasicSet = string | ident | char [".." char] | "ANY".
SetDecl

associates a name with a character set. Basic character sets are denoted as:

string
ident
char
char1..char2
ANY

a set consisting of all the characters in the string
a previously declared character set with this name
a set containing the character char
the set of all characters from char1 to char2
the set of all characters in the range 0 .. 65535

Character sets may be formed from basic sets using the operators
set union
set difference

+
-

Examples
digit
hexDigit
letter
eol
noDigit

=
=
=
=
=

"0123456789".
digit + "ABCDEF".
'A' .. 'Z'.
'\r'.
ANY - digit.

/*
/*
/*
/*
/*

the
the
the
the
any

set of all digits */
set of all hexadecimal digits */
set of all upper case letters */
end-of-line character */
character that is not a digit */

8

2.3.2 Tokens
This is the main section of the scanner specification, in which the tokens (or terminal
symbols) of the language are declared. Tokens may be divided into literals and token
classes.
 Literals (such as while or >=) have a fixed representation in the source language. In
the grammar they are written as strings (e.g. "while" or ">=") and denote
themselves. They don't have to be declared in the tokens section but are implicitly
declared at their first use in the productions of the grammar.
 Token classes (such as identifiers or numbers) have a certain structure that must be
explicitly declared by a regular expression in EBNF. There are usually many
instances of a token class (e.g. many different identifiers), which have the same
token code, but different lexeme values.
The syntax of token declarations is as follows:
TokenDecl
TokenExpr
TokenTerm
TokenFactor

Symbol

=
=
=
=
|
|
|
=

Symbol ['=' TokenExpr '.'].
TokenTerm {'|' TokenTerm}.
TokenFactor {TokenFactor} ["CONTEXT" '(' TokenExpr ')'].
Symbol
'(' TokenExpr ')'
'[' TokenExpr ']'
'{' TokenExpr '}'.
ident | string | char.

A token declaration defines the syntax of a terminal symbol by a regular EBNF expression. This expression may contain strings or character constants denoting
themselves (e.g. ">=" or ';') as well as names of character sets (e.g. letter) denoting
an arbitrary character from this set. It must not contain other token names, which
implies that EBNF expressions in token declarations cannot be recursive.
Examples
ident = letter {letter | digit | '_'}.
number = digit {digit}
| "0x" hexDigit hexDigit hexDigit hexDigit.
float = digit {digit} '.' {digit} ['E' ['+'|'-'] digit {digit}].

The token declarations need not be LL(1) as can be seen in the declaration of number,
where both alternatives can start with a '0'. Coco/R automatically resolves any
ambiguities and generates a deterministic finite scanner automaton.
Tokens may be declared in any order. However, if a token is declared as a literal that
matches an instance of a more general token, the literal has to be declared after the
more general token.
Example
ident = letter {letter | digit}.
while = "while".

Since the string "while" matches both the tokens while and ident, the declaration of
while must come after the declaration of ident. In principle, literal tokens don't have
to be declared in the token declarations at all, but can simply be introduced directly in
the productions of the grammar. In some situations, however, it makes sense to
declare them explicitly, for example, in order to get a token name for them that can be
used in resolver methods (see Section 2.4.6).

9

Context-dependent tokens. The CONTEXT phrase in a TokenTerm means that the term is
only recognized if its context (i.e. the characters that follow the term in the input
stream) matches the TokenExpr specified in brackets. Note that the TokenExpr is not
part of the token.
Example
number = digit {digit}
| digit {digit} CONTEXT ("..").
float = digit {digit} '.' {digit} ['E' ['+'|'-'] digit {digit}].

The CONTEXT phrase in this example allows the scanner to distinguish between float
tokens (e.g. 1.23) and integer ranges (e.g. 1..2) that could otherwise not be scanned
with a single character lookahead. This works as follows: after having read "1." the
scanner still works on both tokens. If the next character is a '.' the characters ".."
are pushed back to the input stream and a number token with the value 1 is returned to
the parser. If the next character is not a '.' the scanner continues with the recognition
of a float token.
Hand-written scanners. If the right-hand sides of the token declarations are missing
no scanner is generated. This gives the user the chance to provide a hand-written
scanner, which must conform to the interface described in Section 3.4.1.
Example
TOKENS
ident
number
"if"
"while"
...

Tokens are assigned numbers in the order of their declaration. The first token gets the
number 1, the second the number 2, and so on. The number 0 is reserved for the endof-file token. The hand-written scanner must return the token numbers according to
these conventions. In particular, it must return an end-of-file token if no more input is
available.
It is hardly ever necessary to supply a hand-written scanner, because the scanner
generated by Coco/R is highly optimized. A user-supplied scanner would be needed,
for example, if the scanner were required to process include directives.

2.3.3 Pragmas
Pragmas are tokens that may occur anywhere in the input stream (for example, endof-line symbols or compiler directives). It would be too tedious to handle all their
possible occurrences in the grammar. Therefore they are excluded from the token
stream that is passed to the parser. Pragmas are declared like tokens, but they may
have a semantic action associated with them that is executed whenever they are
recognized by the scanner.
PragmaDecl = TokenDecl [SemAction].
SemAction = "(." ArbitraryStatements ".)".

10

Example
PRAGMAS
option = '$' {letter}.

(. foreach (char ch in la.val)
if (ch == 'A') ...
else if (ch == 'B') ...
... .)

This pragma defines a compiler option that can be written, for example, as $A.
Whenever it occurs in the input stream it is not forwarded to the parser but
immediately processed by executing its associated semantic action. Note that la.val
accesses the value of the lookahead token la, which is in this case the pragma that
was just read (see Section 3.4.4).

2.3.4 Comments
Comments are difficult to specify with regular expressions; nested comments are even
impossible to specify that way. This makes it necessary to have a special construct to
define their structure.
Comments are declared by specifying their opening and closing brackets. The
keyword NESTED denotes that they can be nested.
CommentDecl = "COMMENTS" "FROM" TokenExpr "TO" TokenExpr ["NESTED"].

Comment delimiters must be sequences of 1 or 2 characters, which can be specified as
literals or as single-element character sets. They must not be structured (for example
with alternatives). It is possible to declare multiple kinds of comments.
Example
COMMENTS FROM "/*" TO "*/" NESTED
COMMENTS FROM "//" TO eol

Alternatively, if comments cannot be nested one can define them as pragmas, e.g.:
CHARACTERS
other = ANY - '/' - '*'.
PRAGMAS
comment = "/*" {'/' | other | '*' {'*'} other} '*' {'*'} '/'.

This has the advantage that such comments can be processed semantically, for
example, by counting them or by processing compiler options within them.

2.3.5 White space
Characters such as blanks, tabulators or end-of-line symbols are usually considered as
white space that should be ignored by the scanner. Blanks are ignored by default. If
other characters should be ignored as well the user has to specify them in the
following way:
WhiteSpaceDecl = "IGNORE" Set.

Example
IGNORE '\t' + '\r' + '\n'

11

2.3.6 Case sensitivity
Some languages such as Pascal are case insensitive. In Pascal, for example, one can
write the keyword while also as While or WHILE. By default, Coco/R generates
scanners that are case sensitive. If this is not desired, one has to write IGNORECASE at
the beginning of the scanner specification.
The effect of IGNORECASE is that all input to the scanner is treated in a case-insensitive
way. The production
WhileStatement = "while" '(' Expr ')' Statement.

will therefore also recognize while statements that start with
Similarly, the declaration:

While

or

WHILE.

TOKENS
float = digit {digit} '.' ['E' ('+'|'-') digit {digit}].

will cause the scanner to recognize not only 1.2E2 but also 1.2e2 as a float token.
However, the original casing of tokens is preserved in the val field of every token
(see Section 3.4.2) so that the lexical value of tokens such as identifiers and strings is
delivered exactly as it was written in the input text.

2.4 Parser Specification
The parser specification is the main part of a compiler description. It contains the
productions of an attributed grammar, which specify the syntax of the language to be
parsed as well as its translation.
ParserSpecification = "PRODUCTIONS" {Production}.
Production = ident [FormalAttributes] [LocalDecl] '=' Expression '.'.
Expression = Term {'|' Term}.
Term
= [[Resolver] Factor {Factor}].
Factor
= ["WEAK"] Symbol [ActualAttributes]
| '(' Expression ')'
| '[' Expression ']'
| '{' Expression '}'
| "ANY"
| "SYNC"
| SemAction.
Symbol
= ident | string | char.
SemAction = "(." ArbitraryStatements ".)".
LocalDecl = SemAction.
FormalAttributes = '<' ArbitraryText '>'.
ActualAttributes = '<' ArbitraryText '>'.
Resolver
= "IF" '(' {ANY} ')'.

2.4.1 Productions
A production specifies the syntactical structure of a nonterminal symbol. It consists of
a left-hand side and a right-hand side which are separated by an equal sign. The lefthand side specifies the name of the nonterminal together with its formal attributes and
the local variables of the production. The right-hand side consists of an EBNF
expression that specifies the structure of the nonterminal as well as its translation in
form of attributes and semantic actions.
The productions may be given in any order. References to as yet undeclared
nonterminals are allowed. For every nonterminal there must be exactly one
production. In particular, there must be a production for the grammar name, which is
the start symbol of the grammar.

12

2.4.2 Semantic Actions
A semantic action is a piece of code written in the target language of Coco/R (i.e. in
C#, Java or C++). It is executed by the generated parser at the position where it has
been specified in the grammar. Semantic actions are simply copied to the generated
parser without being checked by Coco/R.
A semantic action can also contain the declarations of local variables. Every
production has its own set of local variables, which are retained in recursive
productions. The optional semantic action on the left-hand side of a production
(LocalDecl) is intended for such declarations, but variables can also be declared in any
other semantic action.
Here is an example that counts the number of identifiers in an identifier list:
IdentList =
ident
{',' ident
}
.

(. int n = 1; .)
(. n++; .)
(. Console.WriteLine("n = " + n); .)

As a matter of style, it is good practice to write all syntax parts on the left side and all
semantic actions on the right side of a page. This makes a production better readable
because the syntax is separated from its processing.
Semantic actions cannot only access local variables but also fields and methods
declared at the beginning of the attributed grammar (see Section 2.2) as well as fields
and methods of imported classes.

2.4.3 Attributes
Productions are considered as (and are actually translated to) parsing methods. The
occurrence of a nonterminal on the right-hand side of a production can be viewed as a
call of that nonterminal's parsing method.
Nonterminals may have attributes, which correspond to parameters of the nonterminal's parsing method. There are input attributes, which are used to pass values to the
production of a nonterminal, and output attributes, which are used to return values
from the production of a nonterminal to its caller (i.e. to the place where this
nonterminal occurs in some other production).
As with parameters, we distinguish between formal attributes, which are specified at
the nonterminal's declaration on the left-hand side of a production, and actual
attributes, which are specified at the nonterminal's occurrence on the right-hand side
of a production.
Attributes are enclosed in angle brackets (e.g., < ... >). If attributes contain the
operators '<' or '>' or generic types like List the attribute brackets must be
written as <. ... .>.
Coco/R checks that nonterminals with attributes are always used with attributes and
that nonterminals without attributes are always used without attributes. However, it
does not check the correspondence between formal and actual attributes, which is left
to the compiler of the target language.

13
Attributes in C#. A formal attribute looks like a parameter declaration. In C#, output
attributes must be preceded by the keyword out or ref. The following example
declares a nonterminal S with an input attribute x and two output attributes y and z:
S  = ... .

An actual attribute looks like an actual parameter. Actual input attributes may be
expressions, which are evaluated and assigned to the corresponding formal attributes.
In C#, actual output attributes must be preceded by the keywords out or ref. They are
passed by reference like output parameters in C#. Here is an example (a and b are
assumed to be of type int, c is assumed to be of type string):
... S <3*a + 1, out b, ref c> ...

The production of the nonterminal S is translated to the following parsing method:
void S(int x, out int y, ref string z) {
...
}

Attributes in Java. Since Java does not support output parameters, the Java version
of Coco/R allows only a single output attribute which is passed to the caller as a
return value. However, the return value can be an object of a class that contains
multiple values.
If a nonterminal has an output attribute it must be the first attribute. It is denoted by
the keyword out both in its declaration and in its use. The following example shows a
nonterminal S with an output attribute x and two input attributes y and z (for
compatibility with older versions of Coco/R the symbol '^' can be substituted for the
keyword out):
S = ... .

This nonterminal is used as follows:
... S ...

The production of the nonterminal T is translated to the following parsing method:
int S(char y, int z) {
int x;
...
return x;
}

Attributes in C++. In the C++ version of Coco/R, input attributes are translated to
value parameters and output attributes to reference parameters. The following
example declares a nonterminal S with an input attribute x and an output attribute y:
S = ... .

Actual attributes are written like actual parameters in C++, i.e., there is no distinction
between value parameters and reference parameters:
... S ...

Attributes of terminal symbols. Terminal symbols do not have attributes in Cocol/R.
For every token, however, the scanner returns the token value (i.e. the token's string
representation) as well as the line and column number of the token (see Section 3.4.4).
This information can be viewed as output attributes of that token. If users want to
access this data they can wrap a token into a nonterminal with the desired attributes,
for example:

14
Ident  =
ident
(. name = t.val; .) .
Number  =
number
(. value = Convert.ToInt32(t.val); .) .

The variable t is the most recently recognized token. Its field
representation of the token (see Section 3.4.4).

t.val

holds the textual

2.4.4 The Symbol ANY
In the productions of the grammar the symbol ANY denotes any token that is not an
alternative to that ANY symbol in the current production. It can be used to conveniently
parse structures that contain arbitrary text. The following production, for example,
processes an attribute list in Cocol/R and returns the number of characters between
the angle brackets:
Attributes < out int len> =
'<'
(. int beg = t.pos + 1; .)
{ANY}
'>'
(. len = t.pos - beg; .) .

In this example the token '>' is an implicit alternative of the ANY symbol in curly
braces. The meaning is that this ANY matches any token except '>'. t.pos is the source
text position of the most recently recognized token (see Section 3.4.4).
Here is another example that counts the number of statements in a block:
Block  = (. int n; .)
'{'
(. stmts = 0; .)
{ ';'
(. stmts++; .)
| Block
(. stmts += n; .)
| ANY
}
'}'.

In this example the ANY matches any token except ';',
alternatives of it ('{' is a terminal start symbol of Block).

'{'

and

'}'

which are

2.4.5 LL(1) Conflicts
Recursive descent parsing requires that the grammar of the parsed language is LL(1)
(i.e. parsable from Left to right with Left-canonical derivations and 1 lookahead
symbol). This means that at any point in the grammar the parser must be able to
decide on the basis of a single lookahead symbol which of several possible
alternatives have to be selected. The following production, for example, is not LL(1):
Statement = ident '=' Expression ';'
| ident '(' [ActualParameters] ')' ';'
| ... .

Both alternatives start with the symbol ident. When the parser comes to the beginning
of a Statement and ident is the next input token, it cannot distinguish between the two
alternatives. However, this production can easily be transformed to
Statement = ident ( '=' Expression ';'
| '(' [ActualParameters] ')' ';'
)
| ... .

where all alternatives start with distinct symbols and the LL(1) conflict has disappeared.

15
LL(1) conflicts can arise not only from explicit alternatives like those in the example
above but also from implicit alternatives that are hidden in optional or iterative EBNF
expressions. The following list shows how to check for LL(1) conflicts in these
situations (Greek symbols denote arbitrary EBNF expressions such as a[b]C; first(α)
denotes the set of terminal start symbols of the EBNF expression α; follow(A) denotes
the set of terminal symbols that can follow the nonterminal A in any other production):
 Explicit alternatives
A = α|β|γ.
A =(α|)β.
A =(α|).

check that first(α) ∩ first(β) = {} ∧ first(α) ∩ first(γ) = {} ∧ first(β) ∩ first(γ) = {}.
check that first(α) ∩ first(β) = {}
check that first(α) ∩ follow(A) = {}

 Options
A = [α] β.
A = [α].

check that first(α) ∩ first(β) = {}
check that first(α) ∩ follow(A) = {}

 Iterations
A = {α} β. check that first(α) ∩ first(β) = {}
A = {α}.
check that first(α) ∩ follow(A) = {}

It would be very tedious and error-prone to check all these conditions manually for a
grammar of a realistic size. Fortunately, Coco/R does that automatically. For example,
the grammar
A = (a | B C d).
B = [b] a.
C = c {d}.

will result in the following LL(1) warnings:
LL1 warning in A: a is start of several alternatives
LL1 warning in C: d is start & successor of deletable structure

The first conflict arises because B can start with an a. The second conflict comes from
the fact that C may be followed by a d, and so the parser does not know whether it
should do another iteration of {d} in C or terminate C and continue with the d outside.
Another situation that leads to a conflict is when an expression in curly or square
brackets is deletable, e.g.:
A = [B] a.
B = {b}.

If the parser tries to recognize A and sees an a it cannot decide whether to enter the
deletable symbol B or to skip [B]. Therefore Coco/R prints the warning:
LL1 warning in A: contents of [...] or {...} must not be deletable

Note that Coco/R reports LL(1) conflicts as warnings, not as errors. Whenever the
parser sees two or more alternatives that can start with the same token it always
chooses the first one. If this is what the user intends then everything is fine, like in the
well-known example of the dangling else that occurs in many programming
languages:
Statement = "if" '(' Expression ')' Statement ["else" Statement]
| ... .

Input for this grammar like
if (a > b) if (a > c) max = a; else max = b;

16

is ambiguous: does the "else" belongs to the inner or to the outer if statement? The
LL(1) conflict arises because
first("else"

Statement) ∩

follow(Statement) = {"else"}

However, this is not a big problem, because the parser chooses the first matching
alternative, which is the "else" of the inner if statement. This is exactly what we
want.
Resolving LL(1) conflicts by grammar transformations
If Coco/R reports an LL(1) conflict the user should try to eliminate it by transforming
the grammar as it is shown in the following examples.
Factorization. Most LL(1) conflicts can be resolved by factorization, i.e. by extracting the common parts of conflicting alternatives and moving them to the front. For
example, the production
A = a b c | a b d.

can be transformed to
A = a b (c | d).

Left recursion. Left recursion always represents an LL(1) conflict. In the production
A = A b | c.

both alternatives start with c (because first(A) = {c}). However, left recursion can
always be transformed into an iteration, e.g. the previous production becomes
A = c {b}.

Hard conflicts. Some LL(1) conflicts cannot be resolved by grammar transformations. Consider the following (simplified) productions from the C# grammar:
Expr
= Factor {'+' Factor}.
Factor = '(' ident ')' Factor
| '(' Expr ')'
| ident | number.

/* type cast */
/* nested expression */

The conflict arises, because two alternatives of Factor start with '('. Even worse,
Expr can also be derived to an ident. There is no way to get rid of this conflict by
transforming the grammar. The only way to resolve it is to look at the ident following
the '(': if it denotes a type the parser has to select the first alternative otherwise the
second one. We will deal with this kind of conflict resolution in Section 2.4.6.
Readability issues. Some grammar transformations can degrade the readability of the
grammar. Consider the following example (again taken from a simplified form of the
C# grammar):
UsingClause = "using" [ident '='] Qualident ';'.
Qualident
= ident {'.' ident}.

The conflict is in UsingClause where both [ident '='] and Qualident start with
ident. Although this conflict could be eliminated by transforming the production to
UsingClause = "using" ident ( {'.' ident}
| '=' Qualident
) ';'.

the readability would clearly deteriorate. It is better to resolve this conflict as shown
in Section 2.4.6.

17
Semantic issues. Finally, factorization is sometimes inhibited by the fact that the semantic processing of conflicting alternatives differs, e.g.:
A = ident (. x = 1; .) {',' ident (. x++; .) } ':'
| ident (. Foo(); .) {',' ident (. Bar(); .) } ';'.

The common parts of these two alternatives cannot be factored out, because each
alternative has its own way to be processed semantically. Again this problem can be
solved with the technique explained in Section 2.4.6.

2.4.6 LL(1) Conflict Resolvers
A conflict resolver is a boolean expression that is inserted into the grammar at the
beginning of the first of two conflicting alternatives and decides, using a multisymbol lookahead or a semantic check, whether this alternative matches the actual
input. If the resolver yields true, the alternative prefixed by the resolver is selected,
otherwise the next alternative will be checked. A conflict resolver is written as
Resolver = "IF" '(' ... any expression ... ')' .

where any boolean expression can be written between the parentheses. In most cases
this will be a function call that returns true or false.
Thus we can resolve the LL(1) conflict from Section 2.4.5 in the following way:
UsingClause = "using" [IF(IsAlias()) ident '='] Qualident ';'.
IsAlias is a user-defined method that reads two tokens ahead. It returns true, if ident
is followed by '=', otherwise it returns false.

Conflict resolution by a multi-symbol lookahead
The generated parser remembers the most recently recognized token as well as the
current lookahead token in two global variables (see also Section 3.4.4):
Token t; // most recently recognized token
Token la; // lookahead token

The generated scanner offers a method Peek() that can be used to read ahead beyond
the lookahead token without removing any tokens from the input stream. When
normal parsing resumes the scanner will return these tokens again.
With Peek() we can implement IsAlias() in the following way:
bool IsAlias() {
Token next = scanner.Peek();
return la.kind == _ident && next.kind == _eql;
}

The conflict mentioned at the end of Section 2.4.5 can be resolved by the production
A = IF(FollowedByColon())
ident (. x = 1; .) {',' ident (. x++; .) } ':'
| ident (. Foo(); .) {',' ident (. Bar(); .) } ';'.

and the following implementation of the function FollowedByColon():
bool FollowedByColon() {
Token x = la;
while (x.kind == _comma || x.kind == _ident)
x = scanner.Peek();
return x.kind == _colon;
}

18
Token names. For peeking it is convenient to be able to refer to the token numbers by
names such as _ident or _comma. Coco/R generates such names for all tokens declared
in the TOKENS section of the scanner specification. For example, if the tokens are
declared like this:
TOKENS
ident
number
eql
comma
colon

=
=
=
=
=

letter {letter | digit}.
digit {digit}.
'=';
','.
':'.

Coco/R will generate the following constant declarations in the parser:
const
const
const
const
const
const

int
int
int
int
int
int

_EOF = 0;
_ident = 1;
_number = 2;
_eql = 3;
_comma = 4;
_colon = 5;

The token names are preceded by an underscore in order to avoid conflicts with
reserved keywords and other identifiers.
Normally the TOKENS section will only contain declarations for token classes like
ident or number. However, if the name of a literal token is needed for peeking, it has
to be declared there as well. In the productions of the grammar this token can then be
referred to either by its name (e.g. _comma) or by its literal value (e.g. ',').
Resetting the peek position. The scanner makes sure that a sequence of Peek() calls
will return the tokens following the lookahead token la. In rare situations, however,
the user has to reset the peek position manually. Consider the following grammar:
A = ( IF (IsFirstAlternative()) ...
| IF (IsSecondAlternative()) ...
| ...
).

Assume that the function IsFirstAlternative() starts peeking and finds out that the
input does not match the first alternative. So it returns false and the parser checks the
second alternative. The function IsSecondAlternative() starts peeking again, but
before that, it should reset the peek position to the first symbol after the lookahead
token la. This can be done by calling scanner.ResetPeek().
bool IsSecondAlternative() {
scanner.ResetPeek();
Token x = scanner.Peek(); // returns the first token after the
...
// lookahead token again
}

The peek position is reset automatically every time a regular token is recognized by
scanner.Scan() (see Section 3.4.1).
Translation of conflict resolvers. Coco/R treats resolvers like semantic actions and
simply copies them into the generated parser at the position where they appear in the
grammar. For example, the production
UsingClause = "using" [IF(IsAlias()) ident '='] Qualident ';'.

is translated into the following parsing method:

19

void UsingClause() {
Expect(_using);
if (IsAlias()) {
Expect(_ident);
Expect(_eql);
}
Qualident();
Expect(_semicolon);
}

Conflict resolution by exploiting semantic information
A conflict resolver can base its decision not only on lookahead tokens but also on any
other information. For example it could access a symbol table to find out semantic
properties about a token. Consider the following LL(1) conflict between type casts
and nested expressions, which can be found in many programming languages:
Expr
= Factor {'+' Factor}.
Factor = '(' ident ')' Factor
| '(' Expr ')'
| ident | number.

/* type cast */
/* nested expression */

Since Expr can start with an ident as well the conflict can be resolved by checking
whether this ident denotes a type or some other object:
Factor = IF (IsCast())
'(' ident ')' Factor
| '(' Expr ')'
| ident | number.
IsCast()

/* type cast */
/* nested expression */

looks up ident in the symbol table and returns true, if it is a type name:

bool IsCast() {
Token x = scanner.Peek();
if (la.kind == _lpar && x.kind == _ident) {
object obj = symTab.Find(x.val);
return obj != null && obj.kind == Type;
} else return false;
}

Placing resolvers correctly
Coco/R checks if resolvers are placed correctly. The following rules must be obeyed:
1. If two alternatives start with the same token, the resolver must be placed in front
of the first one. Otherwise it would never be executed because the parser would
always choose the first matching alternative. More precisely, a resolver must be
placed at the earliest possible point where an LL(1) conflict arises.
2. A resolver may only be placed in front of an alternative that is in conflict with
some other alternative. Otherwise it would be illegal.
Here is an example of incorrectly placed resolvers:
A =
( a (IF (...) b) c
| IF (...) a b
| IF (...) b
).

// misplaced resolver. No LL(1) conflict.
// resolver not evaluated. Place it at first alt.
// misplaced resolver. No LL(1) conflict

20

Here is how the resolvers should have been placed in this example:
A =
( IF (...) a b
| a c
| b
).

// resolves conflict betw. the first two alternatives

The following example is also interesting:
A
{
|
}

=
a
IF (...) b c
b.

// resolver placed incorrectly.

Although the b in the second alternative constitutes an LL(1) conflict with the b after
the iteration, the resolver is placed incorrectly. It should rather be placed at the
beginning of the iteration like this:
A =
{ IF (AnotherIteration())
( a
| b c
)
} b.

The function AnotherIteration() could then be implemented as follows:
bool AnotherIteration() {
Token next = scanner.Peek();
return la.kind == _a ||
la.kind == _b && next.kind == _c;
}

The reason why this resolver is placed incorrectly is that it should be called only once
in the parser (namely in the header of the while loop):
void A() {
while (AnotherIteration()) {
if (la.kind == _a)
Expect(_a);
else if (la.kind == _b) {
Expect(_b); Expect(_c);
}
}
Expect(_b);
}

and not both in the while header and at the beginning of the second alternative.
Remember, that the resolver must be placed at the earliest possible point where the
LL(1) conflict arises.

2.4.7 Syntax Error Handling
If a syntax error is detected during parsing the generated parser reports the error and
tries to recover by synchronizing the erroneous input with the grammar. While error
messages are generated automatically, the user has to give certain hints in the
grammar in order to enable the parser to recover from errors.
Invalid terminal symbols. If a certain terminal symbol was expected but not found in
the input the parser just reports that this symbol was expected. For example, if we had
a production
A = a b c.

21
for which the input was
a x c

the parser reports
-- line ... col ...: b expected

Invalid alternative lists. If the lookahead symbol does not match any alternative
from a list of expected alternatives in a nonterminal A the parser just reports that A was
invalid. For example, if we had a production
A = a (b|c|d) e.

for which the input was
a x e

the parser reports
-- line ... col ...: invalid A

Obviously, this error message can be improved if we turn the alternative list into a
separate nonterminal symbol, i.e.:
A = a B e.
B = b|c|d.

In this case the error message would be
-- line ... col ...: invalid B

which is more precise.
Synchronization. After an error was reported the parser continues until it gets to a socalled synchronization point where it tries to synchronize the input with the grammar
again. Synchronization points have to be specified by the keyword SYNC . They are
points in the grammar where particularly safe tokens are expected, i.e. tokens that
hardly occur anywhere else and are unlikely to be mistyped. When the parser reaches
a synchronization point it skips all input until a token occurs that is expected at this
point.
In many languages good candidates for synchronization points are the beginning of a
statement (where keywords like if, while or for are expected) or the beginning of a
declaration sequence (where keywords like public, private or void are expected). A
semicolon is also a good synchronization point in a statement sequence.
The following production, for example, specifies the beginning of a statement as well
as the semicolon after an assignment as synchronization points:
Statement =
SYNC
( Designator '=' Expression SYNC ';'
| "if" '(' Expression ')' Statement ["else" Statement]
| "while" '(' Expression ')' Statement
| '{' {Statement} '}'
| ...
).

In the generated parser, these synchronization points look as follows (written in
pseudo code here):

22

void Statement() {
while (la.kind ∉ {_EOF, _ident, _if, _while, _lbrace, ...}) {
Report an error;
Get next token;
}
if (la.kind == _ident) {
Designator(); Expect(_eql); Expression();
while (la.kind ∉ {_EOF, _semicolon}) {
Report an error;
Get next token;
}
} else if (la.kind == _if) { ...
} ...
}

Note that the end-of-file symbol is always included in the set of synchronization
symbols. This guarantees that the synchronization loop terminates at least at the end
of the input.
In order to avoid a proliferation of error messages during synchronization, an error is
only reported if at least two tokens have been recognized correctly since the last error.
Normally there are only a handful of synchronization points in a grammar for a real
programming language. This makes error recovery cheap in Coco/R and does not
slow down error-free parsing.
Weak tokens. Error recovery can further be improved by specifying tokens that are
"weak" in a certain context. A weak token is a symbol that is often mistyped or
missing such as a comma in a parameter list, which is often mistyped as a semicolon.
A weak token is preceded by the keyword WEAK. When the parser expects a weak
token but does not find it in the input stream it adjusts the input to the next token that
is either a legal successor of the weak token or a token expected at any synchronization point (symbols expected at synchronization points are considered to be
particularly "strong" so that it makes sense to never skip them).
Weak tokens are often separator symbols that occur at the beginning of an iteration.
For example, if we have the productions
ParameterList = '(' Parameter {WEAK ',' Parameter} ')'.
Parameter = ["ref"|"out"] Type ident.

and the parser does not find a ',' or a ')' after the first parameter it reports an error
and skips the input until it finds either a legal successor of the weak token (i.e., a legal
start of Parameter), or a successor of the iteration (i.e. ')'), or any symbol expected at
a synchronization point (including the end-of-file symbol). The effect is that the
parsing of the parameter list would not be terminated prematurely but would get a
chance to synchronize with the start of the next parameter after a possibly mistyped
separator symbol.
In order to get good error recovery the user of Coco/R should perform some
experiments with erroneous inputs and place SYNC and WEAK keywords appropriately to
recover from the most likely errors.

23

2.4.8 Frame Files
The scanner and the parser are generated from template files with the names
Scanner.frame and Parser.frame. Those files contain fixed code parts as well as
textual markers that denote positions at which grammar-specific parts are inserted by
Coco/R. In rare situations advanced users may want to modify the fixed parts of the
frame files by which they can influence the behavior of the scanner and the parser to a
certain degree. Optionally, a file named Copyright.frame can be provided, which will
be included at the top of the generated scanner and parser.

3. User Guide
3.1 Installation
Coco/R can be downloaded from http://ssw.jku.at/Coco/.
C# and C++ version. Copy the following files to a new directory:
Coco.exe
Scanner.frame
Parser.frame

the executable
the frame file from which the scanner is generated
the frame file from which the parser is generated

Java version. Copy the following files to a new directory:
Coco.jar
Scanner.frame
Parser frame

an archive containing all classes of Coco/R
the frame file from which the scanner is generated
the frame file from which the parser is generated

3.2 Options
Coco/R supports several options that can be provided as command line arguments
(see Section 3.3); some of them can also be provided as directives at the beginning of
the attributed grammar. If an option is provided both as a command line argument and
as a directive in the attributed grammar the command line argument takes precedence.
namespace. The user can specify the namespace (in Java: the package) to which the
generated scanner and parser should belong (e.g. at.jku.ssw.Coco). If no namespace
is specified the generated classes belong to the default namespace. The namespace
can be provided as a command line argument or as a directive in the attributed
grammar, in which case it has to have the form:
$namespace=namespaceName

(in Java: $package=packageName)

frames. The command line option frames can be used to specify the directory that
contains the frame files Scanner.frame, Parser.frame and optionally Copyright.frame
(see Section 2.4.8). If this option is missing Coco/R expects the frame files to be in
the same directory as the attributed grammar.
output directory. The command line option o specifies the output directory for the
generated scanner and parser. By default, the output directory is the one that contains
the attributed grammar.

24
checkEOF. With the option checkEOF the user can specify whether the generated
parser should check if the entire input has been consumed after parsing, i.e., if the
token after the start symbol of the grammar is an end-of-file token. The user can
enable or disable this check by the following directive in the attributed grammar:
$checkEOF=true
$checkEOF=false

// enable the end of file check (default)
// disable the end of file check

trace. The option trace allows the user to specify a string of switches (e.g. ASX) that
cause internal data structures of Coco/R to be dumped to the file trace.txt. The
switches are denoted by the following characters:
A
F
G
I
J
P
S
X

print the states of the scanner automaton
print the first sets and follow sets of all nonterminals
print the syntax graph of all productions
trace the computation of first sets
list the ANY and SYNC sets used in error recovery
print statistics about the run of Coco/R
print the symbol table and the list of declared literals
print a cross reference list of all terminals and nonterminals

These switches can be set on in the command line or by a directive in the attributed
grammar, which has the form:
${letter}

For example, the option $ASX will cause the states of the automaton, the symbol table
and a cross reference list to be printed to the file trace.txt.

3.3 Invocation
Coco/R can be invoked from the command line as follows:
C# or C++:
Java:

Coco fileName [Options]
java -jar Coco.jar fileName [Options]

fileName is the name of the file containing the Cocol/R compiler description. As a
convention, compiler descriptions have the extension .ATG (for attributed grammar).

Options. The following options can be specified:
Options =
{ "-namespace" namespaceName
| "-frames" framesDirectory
| "-trace" traceString
| "-o" outputDirectory
}.

// in Java: "-package" packageName

A detailed description of these options can be found in Section 3.2.
Output files. Coco/R translates an attributed grammar into the following files:


Scanner.cs (in Java: Scanner.java; in C++: Scanner.h and Scanner.cpp) containing
the classes Scanner, Token and Buffer .
 Parser.cs (in Java: Parser.java; in C++: Parser.h and Parser.cpp) containing the
classes Parser and Errors.
 trace.txt containing trace output (if any).

By default, all files are generated in the directory containing the attributed grammar.

25

3.4 Interfaces of the Generated Classes
This section specifies the interfaces for the C# version of Coco/R. For Java and C++
the interfaces differ slightly (see the frame files Scanner.frame and Parser.frame).

3.4.1 Scanner
The generated scanner has the following interface:
public class Scanner {
public Buffer buffer;
public
public

Scanner(string sourceFile);
Scanner(Stream s);

public Token
public Token
public void

Scan();
Peek();
ResetPeek();

}

The main class of the compiler (see Section 3.5) has to create a scanner object and
pass it either an input stream or the name of a file from where the tokens should be
read. The scanner's input buffer is exported in the field buffer. It can be used to
access the input text at random addresses (see Section 3.4.3).
The method Scan() is the actual scanner. The parser calls it whenever it needs the
next token. Once the input is exhausted Scan() returns the end-of-file token, which
has the token number 0. For invalid tokens (caused by illegal token syntax or by
invalid characters) Scan() returns a special token kind, which normally causes the
parser to report an error.
can be used to read one or several tokens ahead without removing them from
the input stream. With every call of Scan() (i.e. every time a token has been
recognized) the peek position is set to the scan position so that the first Peek() after a
Scan() returns the first yet unscanned token. The method ResetPeek() can be used to
reset the peek position to the scan position after several calls of Peek().
Peek()

3.4.2 Token
Every token returned by the scanner is an object of the following class:
public class Token {
public int
kind;
public string val;
public int
pos;
public int
public int
public int

//
//
//
//
charPos; //
//
line;
//
col;
//

token code (EOF has the code 0)
token value
token position in the source text
(in bytes starting at 0)
token position in the source text
(in characters starting at 0)
line number (starting at 1)
column number (starting at 1)

}

3.4.3 Buffer
This is an auxiliary class that is used by the scanner (and possibly by other classes) to
read the source stream into a buffer and retrieve portions of it:

26

public class Buffer {
public const int EOF = char.MaxValue + 1;
public
public
public
public
public

Buffer(Stream s);
int
int
int
string

Read();
Peek();
Pos {get; set;}
GetString(int beg, int end);

}

A buffer is initialized with the source stream. Read() returns the next character or
65536 if the input is exhausted. Peek() allows the scanner to read characters ahead
without consuming them. Pos allows the scanner to get or set the reading position,
which is initially 0. GetString(beg, end) can be used to retrieve the text interval
[beg..end[ from the input stream, where beg and end are byte positions.

3.4.4 Parser
The generated parser has the following interface:
public class Parser {
public Scanner scanner;
public Errors errors;
public Token
t;
public Token
la;

//
//
//
//

the scanner of this parser
the error message stream
most recently recognized token
lookahead token

public

Parser(Scanner scanner);

public void
public void

Parse();
SemErr(string msg);

}

The field t holds the most recently recognized token. It can be used in semantic
actions to access the token value or the token position. The field la holds the
lookahead token, i.e. the first token after t, which has not yet been parsed.
After creating a scanner, the main class of the compiler (see Section 3.5) has to create
a parser object and call its method Parse in order to start parsing.
The method SemErr(msg) can be used to report semantic errors. It calls errors.SemErr
(see Section 3.4.5) and suppresses error messages that are too close to the position of
the previous error, thus avoiding spurious error messages (see Section 2.4.7).

3.4.5 Errors
This class is used to print error messages. Coco/R distinguishes four kinds of errors:
syntax errors, semantic errors, warnings and fatal errors. Here is the interface of
Errors:
class Errors {
public int
count = 0;
public string errorStream = Console.Out;
public string errMsgFormat = "-- line {0} col {1}: {2}";
public
public
public
public
public
}

void
void
void
void
void

SynErr(int line, int col, int n);
SemErr(int line, int col, string msg);
SemErr(string msg);
Warning(int line, int col, string msg);
Warning(string msg);

27
The field

holds the number of errors reported by SynErr and SemErr. The field
errorStream denotes the output stream to which error messages are written. By
default, this is the console, but the error stream can also be set to any other stream.
count

Syntax errors are automatically reported by the generated parser, which calls the
method SynErr. Semantic errors should be reported by calling Parser.SemErr which in
turn calls Errors.SemErr. Warnings can be reported by calling the method Warning.
Warnings do not increase the error counter.
If SynErr and SemErr are called with line and column numbers the error message is
printed in the format specified by the string errMsgFormat, which can be changed by
the user to obtain a custom format. The placeholder {0} is replaced by the line
number, {1} is replaced by the column number, and {2} is replaced by the error
message.
The user can modify the methods SynErr, SemErr and Warning in the file Parser.frame.
This can be used, for example, to collect all error messages in a data structure instead
of writing them to the output stream.
In case of a fatal error from which the compiler cannot recover the user should throw
a FatalError exception.
public class FatalError: Exception { // in Java derived from
public FatalError(string msg);
// RuntimeException (i.e. unchecked)
}

In Coco/R, for example, a FatalError is thrown if the frame files cannot be found or
are corrupt. The user can catch a FatalError in the main method of the compiler and
can terminate the compilation.

3.5 Main Class of the Compiler
The main class of a compiler generated with Coco/R has to be provided by the user. It
has to create a scanner and a parser object, initiate parsing and possibly report the
number of errors detected. In its simplest form it can look like this:
public class Compiler {
public static void Main(string[] arg) {
Scanner scanner = new Scanner(arg[0]);
Parser parser = new Parser(scanner);
parser.Parse();
Console.WriteLine(parser.errors.count + " errors detected");
}
}

28

3.6 Grammar Tests
Coco/R checks if the grammar in the compiler specification is well-formed. This
includes the following tests:
 Completeness
For every nonterminal symbol there must be a production. If a nonterminal
not have a production Coco/R prints the message

X

does

No production for X

 Lack of redundancy
If the grammar contains productions for a nonterminal X that does not occur in any
other productions derived from the start symbol Coco/R prints the message
X cannot be reached

 Derivability
If the grammar contains nonterminals that cannot be derived into a sequence of
terminals, such as in
X = Y ';'.
Y = '(' X ')'.

Coco/R prints the messages
X cannot be derived to terminals
Y cannot be derived to terminals

 Lack of circularity
If the grammar contains circular productions, i.e. if nonterminals can be derived
into themselves (directly or indirectly) such as in
A = [a] B.
B = (C| b).
C = A {c}.

Coco/R prints the messages
A --> B
B --> C
C --> A

 Lack of ambiguity
If two or more tokens are declared so that they can have the same structure and thus
cannot be distinguished by the scanner, as in the following example where the input
123 could either be recognized as an integer or as a float:
TOKENS
integer = digit {digit}.
float
= digit {digit}['.' {digit}].

Coco/R prints the message
Tokens integer and float cannot be distinguished

In all these cases the compiler specification is erroneous and no scanner and parser is
generated.

29

Warnings
There are also situations in grammars that—although legal—might lead to problems.
In such cases Coco/R prints a warning but nevertheless generates a scanner and a
parser. The user should carefully check if these situations are acceptable and, if not,
repair the grammar.
 Deletable symbols
Sometimes, nonterminals can be derived into the empty string such as in the
following grammar:
A = B [a].
B = {b}.

In such cases Coco/R prints the warnings
A deletable
B deletable

 LL(1) conflicts
If two or more alternatives start with the same token such as in
Statement = ident '=' Expression ';'
| ident '(' Parameters ')' ';'.

Coco/R prints the warning
LL(1) warning in Statement: ident is start of several alternatives

If the start symbols and the successors of a deletable EBNF expression
[...] are not disjoint such as in

{...}

QualId = [id '.'] id.
IdList = id {',' id} [','].

Coco/R prints the warnings
LL1 warning in QualId: id is start & successor of deletable structure
LL1 warning in IdList: ',' is start & successor of deletable structure

The resolution of LL(1) conflicts is discussed in Section 2.4.5.

or

30

4. A Sample Compiler
This section shows how to use Coco/R for building a compiler for a tiny programming
language called Taste. Taste bears some similarities with C# or Java. It has variables
of type int and bool as well as functions without parameters. It allows assignments,
procedure calls, if and while statements. Integers may be read from a file and written
to the console, each of them in a single line. It has arithmetic expressions (+,-,*,/) and
relational expressions (==,<,>). Here is an example of a Taste program:
program Test {
int i;

// global variable

// compute the sum of 1..i
void SumUp() {
int sum;
sum = 0;
while (i > 0) { sum = sum + i; i = i - 1; }
write sum;
}
// the program starts here
void Main() {
read i;
while (i > 0) {
SumUp();
read i;
}
}
}

Of course Taste is too restrictive to be used as a real programming language. Its
purpose is just to give you a taste of how to write a compiler with Coco/R.
The Taste compiler is a compile-and-go compiler, which means that it reads a source
program and translates it into a target program which is executed (i.e. interpreted)
immediately after the compilation. In order to run it type
Taste Test.TAS

The file Test.TAS holds the sample program shown above. This file is now compiled
and immediately executed. If a program requires input (like Test.TAS does) the input
file is always Taste.IN. For our sample program Taste.IN looks like this:
3 5 10 0

Classes
Figure 2 shows the classes of the compiler.
Taste
Parser
Scanner SymbolTable CodeGenerator

Figure 2 Classes of the Taste compiler

31
is the main class. It creates the scanner and the parser and then calls the parser
and the interpreter. The symbol table has methods to handle scopes and to store and
retrieve object information. The code generator has methods to emit instructions. It
also contains the interpreter and its data structures. The source code of all classes as
well as the attributed grammar Taste.ATG can be found in Appendix B.
Taste

Target Code
We define an abstract stack machine for the interpretation of Taste programs. The
compiler translates a source program into instructions of that machine, which are then
interpreted. The machine uses the following data structures:
char[]
int[]
int[]
int
int
int

code;
globals;
stack;
top;
pc;
bp;

//
//
//
//
//
//

object code (filled by the compiler)
data area for global variables
stack with frames for local variables
stack pointer (points to next free stack slot)
program counter
base pointer of current frame

The architecture of the Taste VM is shown in Figure 3.
globals

stack

code

0
0

bp

locals of the
calling method
return address
bp of caller
locals of the
current method

pc

progStart

expression stack
top

word-addressed

byte-addressed

Figure 3: Data structures of the Taste VM

Global variables are stored in the word-addressed array globals at fixed addresses.
Local variables are stored in stack frames that are linked with the stack frame of their
caller. They are addressed with a word offset relative to the base pointer (bp) of the
frame. At the end of the topmost stack frame there is the expression stack that is used
for expression evaluation. After every statement the expression stack is empty.
The machine code is stored in the byte-addressed array code. The program counter pc
points to the currently executed instruction. progStart is the address of the Main
method. This is the point where the execution of the program starts.
The machine instructions are described by the following table (the initial values are:
stack[0] = 0; top = 1; bp = 0;):
CONST
LOAD
LOADG
STO
STOG
ADD
SUB
DIV
MUL

n
a
a
a
a

Load constant
Load local variable
Load global variable
Store local variable
Store global variable
Add
Subtract
Divide
Multiply

Push(n);
Push(stack[bp+a]);
Push(globals[a]);
stack[bp+a]=Pop();
globals[a]=Pop();
Push(Pop()+Pop());
Push(-Pop()+Pop());
x=Pop(); Push(Pop()/x);
Push(Pop()*Pop());

32
NEG
EQU
LSS
GTR
JMP
FJMP
READ
WRITE
CALL
RET
ENTER
LEAVE

Negate
Compare if equal
Compare if less
Compare if greater
Jump
Jump if false
Read integer
Write integer
Call method
Return from method
Enter method
Leave method

a
a

a
n

Push(-Pop());
if (Pop()==Pop()) Push(1); else Push(0);
if (Pop()>Pop()) Push(1); else Push(0);
if (Pop() b) max = a; else max = b;
write max;
}

is translated into the following code
1:
4:
5:
8:
9:
12:
15:
18:
19:
22:
25:
28:
31:
34:
37:
40:
41:
42:

ENTER
READ
STO
READ
STO
LOAD
LOAD
GTR
FJMP
LOAD
STO
JMP
LOAD
STO
LOAD
WRITE
LEAVE
RET

3
0
1
0
1
31
0
2
37
1
2
2

Appendix B contains the source code of the following files, which can also be
downloaded from http://ssw.jku.at/Coco/:
Taste.ATG
Taste.cs
SymTab.cs
CodeGen.cs

the attributed grammar
the main program
the symbol table
the code generator and interpreter

5. Applications of Coco/R
Coco/R can be used not only to write proper compilers, but also to build many kinds
of tools that process structured input data. Various people have used Coco/R for the
following applications:
 An analyzer for the static complexity of programs. The analyzer evaluates the kind
of operators and statements, the nesting of statements and expressions as well as the

33
use of local and global variables to obtain a measure of the program complexity and
an indication if the program is well structured.
 A cross reference generator which lists all occurrences of the objects in a program
according to their scope together with information where the objects have been
assigned a value and where they have been referenced.
 An pretty printer which uses the structure and the length of statements for proper
indentation.
 A program which generates an index for books and reports. The index is generated
from a little language that describes page numbers and the keywords occurring on
those pages.
 The front end of a syntax oriented editor. A program is translated into a tree
representation which is the internal data structure of the editor.
 A program that builds a repository of symbols and their relations in a program. The
repository is accessed by a case tool.
 A profiler that inserts counters and timers into the source code of a program and
evaluates them after the program has been run.
 A white-box test tool that inserts counters into the source code of a program to find
out which paths of the programs have been executed.
 Various compilers for special-purpose scripting languages.
 A log file analyzer that reads machine-generated information and evaluates it.

6. Acknowledgements
The author gratefully acknowledges the help of the following people, who contributed
ideas and improvements to Coco/R or ported it to other programming languages:
Pat Terry, Markus Löberbauer, Albrecht Wöß, Csaba Balazs, Frankie Arzu, Peter
Rechenberg, Josef Templ and John Gough.

References
[Möss90] Mössenböck, H.: A Generator for Production Quality Compilers. 3rd Intl. Workshop on
Compiler Compilers (CC'90), Schwerin, LNCS 477, Springer-Verlag 1990
[Terry04] Terry, P.: Compiling with C# and Java. Pearson, 2004.
[Terry97] Terry, P.: Compilers and Compiler Generators – An Introduction Using C++. International
Thomson Computer Press, 1997.
[Wirth77] Wirth, N.: What Can We Do about the Unnecessary Diversity of Notation for Syntactic
Definitions? Communications of the ACM, November 1977
[WLM03] Wöß A., Löberbauer M., Mössenböck H.: LL(1) Conflict Resolution in a Recursive Descent
Compiler Generator, Joint Modular Languages Conference (JMLC'03), Klagenfurt, 2003

34

A. Syntax of Cocol/R
Cocol =
{ANY}

// using clauses in C#, import clauses in Java,
// #include clauses in C++

"COMPILER" ident
{ANY}
// global fields and methods
ScannerSpecification
Parserspecification
"END" ident '.'.

ScannerSpecification =
["IGNORECASE"]
["CHARACTERS" {SetDecl}]
["TOKENS" {TokenDecl}]
["PRAGMAS" {PragmaDecl}]
{CommentDecl}
{WhiteSpaceDecl}.
SetDecl
= ident '=' Set.
Set
= BasicSet {('+'|'-') BasicSet}.
BasicSet
= string | ident | char [".." char] | "ANY".
TokenDecl
= Symbol ['=' TokenExpr '.'].
TokenExpr
= TokenTerm {'|' TokenTerm}.
TokenTerm
= TokenFactor {TokenFactor} ["CONTEXT" '(' TokenExpr ')'].
TokenFactor
= Symbol
| '(' TokenExpr ')'
| '[' TokenExpr ']'
| '{' TokenExpr '}'.
Symbol
= ident | string | char.
PragmaDecl
= TokenDecl [SemAction].
CommentDecl
= "COMMENTS" "FROM" TokenExpr "TO" TokenExpr ["NESTED"].
WhiteSpaceDecl = "IGNORE" (Set | "CASE").

ParserSpecification = "PRODUCTIONS" {Production}.
Production = ident [Attributes] [SemAction] '=' Expression '.'.
Expression = Term {'|' Term}.
Term
= [[Resolver] Factor {Factor}].
Factor
= ["WEAK"] Symbol [Attributes]
| '(' Expression ')'
| '[' Expression ']'
| '{' Expression '}'
| "ANY"
| "SYNC"
| SemAction.
Attributes = '<' {ANY} '>' | "<." {ANY} ".>".
SemAction
= "(." {ANY} ".)".
Resolver
= "IF" '(' {ANY} ')' .

35

B. Sources of the Sample Compiler
B.1 Taste.ATG
COMPILER Taste
const int // types
undef = 0, integer = 1, boolean = 2;
const int // object kinds
var = 0, proc = 1;
public SymbolTable tab;
public CodeGenerator gen;
CHARACTERS
letter = 'A'..'Z' + 'a'..'z'.
digit = '0'..'9'.
TOKENS
ident = letter {letter | digit}.
number = digit {digit}.
COMMENTS FROM "/*" TO "*/" NESTED
COMMENTS FROM "//" TO '\n'
IGNORE '\r' + '\n' + '\t'
PRODUCTIONS
AddOp
=
(. op = Op.ADD; .)
( '+'
| '-'
(. op = Op.SUB; .)
).
/*------------------------------------------------------------------------*/
Expr
(. int type1; Op op; .)
= SimExpr
[ RelOp
SimExpr (. if (type != type1) SemErr("incompatible types");
gen.Emit(op); type = boolean; .)
].
/*------------------------------------------------------------------------*/
Factor
(. int n; Obj obj; string name; .)
=
(. type = undef; .)
( Ident
(. obj = tab.Find(name); type = obj.type;
if (obj.kind == var) {
if (obj.level == 0) gen.Emit(Op.LOADG, obj.adr);
else gen.Emit(Op.LOAD, obj.adr);
} else SemErr("variable expected"); .)
| number
(. n = Convert.ToInt32(t.val);
gen.Emit(Op.CONST, n); type = integer; .)
| '-'
Factor
(. if (type != integer) {
SemErr("integer type expected"); type = integer;
}
gen.Emit(Op.NEG); .)
| "true"
(. gen.Emit(Op.CONST, 1); type = boolean; .)
| "false"
(. gen.Emit(Op.CONST, 0); type = boolean; .)
).
/*------------------------------------------------------------------------*/
Ident
= ident
(. name = t.val; .).
/*------------------------------------------------------------------------*/

36
MulOp
=
(. op = Op.MUL; .)
( '*'
| '/'
(. op = Op.DIV; .)
).
/*------------------------------------------------------------------------*/
ProcDecl
(. string name; Obj obj; int adr; .)
= "void"
Ident
(. obj = tab.NewObj(name, proc, undef); obj.adr = gen.pc;
if (name == "Main") gen.progStart = gen.pc;
tab.OpenScope(); .)
'(' ')'
'{'
(. gen.Emit(Op.ENTER, 0); adr = gen.pc - 2; .)
{ VarDecl | Stat }
'}'
(. gen.Emit(Op.LEAVE); gen.Emit(Op.RET);
gen.Patch(adr, tab.topScope.nextAdr);
tab.CloseScope(); .).
/*------------------------------------------------------------------------*/
RelOp
=
(. op = Op.EQU; .)
( "=="
| '<'
(. op = Op.LSS; .)
| '>'
(. op = Op.GTR; .)
).
/*------------------------------------------------------------------------*/
SimExpr
(. int type1; Op op; .)
= Term
{ AddOp
Term
(. if (type != integer || type1 != integer)
SemErr("integer type expected");
gen.Emit(op); .)
}.
/*------------------------------------------------------------------------*/
Stat
(. int type; string name; Obj obj;
int adr, adr2, loopstart; .)
= Ident
(. obj = tab.Find(name); .)
( '='
(. if (obj.kind != var) SemErr("cannot assign to procedure"); .)
Expr ';' (. if (type != obj.type) SemErr("incompatible types");
if (obj.level == 0) gen.Emit(Op.STOG, obj.adr);
else gen.Emit(Op.STO, obj.adr); .)
| '(' ')' ';'
(. if (obj.kind != proc) SemErr("object is not a procedure");
gen.Emit(Op.CALL, obj.adr); .)
)
| "if"
'(' Expr ')' (. if (type != boolean) SemErr("boolean type expected");
gen.Emit(Op.FJMP, 0); adr = gen.pc - 2; .)
Stat
[ "else"
(. gen.Emit(Op.JMP, 0); adr2 = gen.pc - 2;
gen.Patch(adr, gen.pc);
adr = adr2; .)
Stat
]
(. gen.Patch(adr, gen.pc); .)
| "while"
(. loopstart = gen.pc; .)
'(' Expr ')' (. if (type != boolean) SemErr("boolean type expected");
gen.Emit(Op.FJMP, 0); adr = gen.pc - 2; .)
Stat
(. gen.Emit(Op.JMP, loopstart); gen.Patch(adr, gen.pc); .)
| "read"
Ident ';'

(. obj = tab.Find(name);
if (obj.type != integer) SemErr("integer type expected");
gen.Emit(Op.READ);
if (obj.level == 0) gen.Emit(Op.STOG, obj.adr);
else gen.Emit(Op.STO, obj.adr); .)

37
| "write"
Expr ';'

(. if (type != integer) SemErr("integer type expected");
gen.Emit(Op.WRITE); .)

| '{' { Stat | VarDecl } '}' .
/*------------------------------------------------------------------------*/
Taste
(. string name; .)
= "program"
(. gen.Init(); tab.Init(); .)
Ident
(. tab.OpenScope(); .)
'{'
{ VarDecl | ProcDecl }
'}'
(. tab.CloseScope();
if (gen.progStart == -1) SemErr("main function never defined");
.).
/*------------------------------------------------------------------------*/
Term
(. int type1; Op op; .)
= Factor
{ MulOp
Factor
(. if (type != integer || type1 != integer)
SemErr("integer type expected");
gen.Emit(op); .)
}.
/*------------------------------------------------------------------------*/
Type
=
(. type = undef; .)
( "int"
(. type = integer; .)
| "bool"
(. type = boolean; .)
).
/*------------------------------------------------------------------------*/
VarDecl
(. string name; int type; .)
= Type
Ident
(. tab.NewObj(name, var, type); .)
{ ',' Ident (. tab.NewObj(name, var, type); .)
} ';'.
END Taste.

38

B.2 SymTab.cs (symbol table)
using System;
namespace Taste {
public class Obj { // object decribing a declared name
public string name;
// name of the object
public int type;
// type of the object (undef for procs)
public Obj next;
// to next object in same scope
public int kind;
// var, proc, scope
public int adr;
// address in memory or start of proc
public int level;
// nesting level; 0=global, 1=local
public Obj locals;
// scopes: to locally declared objects
public int nextAdr;
// scopes: next free address in this scope
}
public class SymbolTable {
const int // types
undef = 0, integer = 1, boolean = 2;
const int // object kinds
var = 0, proc = 1, scope = 2;
public int curLevel; // nesting level of current scope
public Obj undefObj; // object node for erroneous symbols
public Obj topScope; // topmost procedure scope
Parser parser;
// open a new scope and make it the current scope (topScope)
public void OpenScope () {
Obj scop = new Obj();
scop.name = ""; scop.kind = scope;
scop.locals = null; scop.nextAdr = 0;
scop.next = topScope; topScope = scop;
curLevel++;
}
// close the current scope
public void CloseScope () {
topScope = topScope.next; curLevel--;
}
// create a new object node in the current scope
public Obj NewObj (string name, int kind, int type) {
Obj p, last, obj = new Obj();
obj.name = name; obj.kind = kind; obj.type = type;
obj.level = curLevel;
p = topScope.locals; last = null;
while (p != null) {
if (p.name == name) parser.SemErr("name declared twice");
last = p; p = p.next;
}
if (last == null) topScope.locals = obj; else last.next = obj;
if (kind == var) obj.adr = topScope.nextAdr++;
return obj;
}

39
// search the name in all open scopes and return its object node
public Obj Find (string name) {
Obj obj, scope;
scope = topScope;
while (scope != null) { // for all scopes
obj = scope.locals;
while (obj != null) { // for all objects in this scope
if (obj.name == name) return obj;
obj = obj.next;
}
scope = scope.next;
}
parser.SemErr(name + " is undeclared");
return undefObj;
}
public SymbolTable (Parser parser) {
this.parser = parser;
topScope = null;
curLevel = -1;
undefObj = new Obj();
undefObj.name = "undef"; undefObj.type = undef; undefObj.kind = var;
undefObj.adr = 0; undefObj.level = 0; undefObj.next = null;
}
} // end SymbolTable
} // end namespace

40

B.3 CodeGen.cs (code generator)
using System;
using System.IO;
namespace Taste {
public enum Op { // opcodes
ADD, SUB, MUL, DIV, EQU, LSS, GTR, NEG,
LOAD, LOADG, STO, STOG, CONST,
CALL, RET, ENTER, LEAVE, JMP, FJMP, READ, WRITE
}
public class CodeGenerator {
string[] opcode =
{"ADD ", "SUB ", "MUL ", "DIV ", "EQU ", "LSS ", "GTR ", "NEG ",
"LOAD ", "LOADG", "STO ", "STOG ", "CONST", "CALL ", "RET ", "ENTER",
"LEAVE", "JMP ", "FJMP ", "READ ", "WRITE"};
public int progStart; // address of first instruction of main program
public int pc;
// program counter
byte[] code = new byte[3000];
// data for Interpret
int[] globals = new int[100];
int[] stack = new int[100];
int top; // top of stack
int bp; // base pointer
//----- code generation methods ----public void Put(int x) { code[pc++] = (byte)x; }
public void Emit (Op op) { Put((int)op); }
public void Emit (Op op, int val) { Emit(op); Put(val>>8); Put(val); }
public void Patch (int adr, int val) {
code[adr] = (byte)(val>>8); code[adr+1] = (byte)val;
}
public void Decode() {
int maxPc = pc; pc = 1;
while (pc < maxPc) {
Op code = (Op)Next();
Console.Write("{0,3}: {1} ", pc-1, opcode[(int)code]);
switch(code) {
case Op.LOAD: case Op.LOADG: case Op.CONST: case Op.STO: case Op.STOG:
case Op.CALL: case Op.ENTER: case Op.JMP: case Op.FJMP:
Console.WriteLine(Next2()); break;
case Op.ADD: case Op.SUB: case Op.MUL: case Op.DIV: case Op.NEG:
case Op.EQU: case Op.LSS: case Op.GTR: case Op.RET: case Op.LEAVE:
case Op.READ: case Op.WRITE:
Console.WriteLine(); break;
}
}
}
//----- interpreter methods ----int Next () {
return code[pc++];
}
int Next2 () {
int x, y;
x = (sbyte)code[pc++]; y = code[pc++];
return (x << 8) + y;
}

41
int Int (bool b) {
if (b) return 1; else return 0;
}
void Push (int val) {
stack[top++] = val;
}
int Pop() {
return stack[--top];
}
int ReadInt(FileStream s) {
int ch, sign, n = 0;
do {ch = s.ReadByte();} while (!(ch >= '0' && ch <= '9' || ch == '-'));
if (ch == '-') {sign = -1; ch = s.ReadByte();} else sign = 1;
while (ch >= '0' && ch <= '9') {
n = 10 * n + (ch - '0');
ch = s.ReadByte();
}
return n * sign;
}
public void Interpret (string data) {
int val;
try {
FileStream s = new FileStream(data, FileMode.Open);
Console.WriteLine();
pc = progStart; stack[0] = 0; top = 1; bp = 0;
for (;;) {
switch ((Op)Next()) {
case Op.CONST: Push(Next2()); break;
case Op.LOAD: Push(stack[bp+Next2()]); break;
case Op.LOADG: Push(globals[Next2()]); break;
case Op.STO: stack[bp+Next2()] = Pop(); break;
case Op.STOG: globals[Next2()] = Pop(); break;
case Op.ADD: Push(Pop()+Pop()); break;
case Op.SUB: Push(-Pop()+Pop()); break;
case Op.DIV: val = Pop(); Push(Pop()/val); break;
case Op.MUL: Push(Pop()*Pop()); break;
case Op.NEG: Push(-Pop()); break;
case Op.EQU: Push(Int(Pop()==Pop())); break;
case Op.LSS: Push(Int(Pop()>Pop())); break;
case Op.GTR: Push(Int(Pop() 0) {
Scanner scanner = new Scanner(arg[0]);
Parser parser = new Parser(scanner);
parser.tab = new SymbolTable(parser);
parser.gen = new CodeGenerator();
parser.Parse();
if (parser.errors.count == 0) {
parser.gen.Decode();
parser.gen.Interpret("Taste.IN");
}
} else {
Console.WriteLine("-- No source file specified");
}
}
}
} // end namespace

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Create Date                     : 2010:11:16 11:22:36+01:00
Creator Tool                    : Acrobat PDFMaker 8.1 for Word
Modify Date                     : 2010:11:16 11:23:01+01:00
Metadata Date                   : 2010:11:16 11:23:01+01:00
Producer                        : Acrobat Distiller 8.2.5 (Windows)
Format                          : application/pdf
Creator                         : Hanspeter Mössenböck
Title                           : The Compiler Generator Coco/R
Document ID                     : uuid:69af2b32-4dee-41f4-b322-6345eb5e286b
Instance ID                     : uuid:510d6bd6-8120-47fa-b858-ffdc2ac64ef3
Company                         : Systemsoftware
Source Modified                 : D:20101116102150
Page Count                      : 42
Page Layout                     : OneColumn
Author                          : Hanspeter Mössenböck

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The Compiler Generator Coco/R User Manual

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