MTB 251
MTB-251 MTB-251
User Manual: MTB-251
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MULTICS TECHNICAL BULLETIN - 251 To! Distribution From: Robert S. Coren Date! 01/22/76 Subject: Canonicalization of Terminal Input page 1 l~lE.Q.Q.L!.t.llQ~ In theory, ~erminal input to Multics is converted by the ring-zero typewriter DIM to "canonical form", i. e., the physical appearance of a line uniquely defines'the form in which it will be stored. In addition, well-defined meanings are attached to input streams containing erase, kill, and escape characters. In actual fact, the current typewriter DIM does not meet the goals described in the preceding paragraph. The three basic types of canonicalization';' re pre sen t s a n e w lin e represents a carri"age return <8S> represents a backspace represents a horizontal tab represents a space {nnn} represents a character whose ASCII nnn (octal) \ is the escape character value is is the erase character @ is the ki lt character lhe examples in the first group illustrate how various typed sequences are canonicalized in terms of column position; these are f 0 1 1 owed b y ex amp 1 es of era s e , k ill , and es cape MULTICS TECHNICAL BULLETIN - page 6 251 canonicalization. In the second group, lines are shown as they appear physically, with no consideration given to the precise sequence of keystrokes that might have produced them. COLUMN CANONICALIlATION EXAMPLES lyped: Nothing special about this line. Appearance: Nothing special about this line. Result: Nothing special about this tine. 1 y oe d : Extraneous white s pace is ignored. Appearance: Extraneous white space is ignored. Resul t: Extraneous white space is ignored. lyped: lwo ways (2<8S>_) to overstrike. ___ Appearance: lWQ Result: l __ w_ O ways (2<8S>_) to overstrike. Typed: Tab + backspace is <8S>reduced to spaces. ways (~) to overstrike. Appearance: Tab + backspace is Result: reduced to spaces. lab + backspace is reduced to spaces. MUL1ICS TECHNICAL BULLET IN - 251 (See rule 9.> ERASE-KlLL AND ESCAPE EXAMPLES Appearance: abz#cde Result: abcde Appearance: ab Result: IIcde abcde Appearance: Not@Never otin Sunday. Result: Never on Sunday. Appearance: ~Q~#~ Result: ~.o.,\; Appearance! ~Q~~W Result: t::!~.!w it's right. it's right. it's right. it's right. (Erase character is overstruck; see Rule 16.> page 7 MUlllCS lECHNlCAl BUllE1IN - Appearance: dcl Result: dcl rrs char (1) 251 page 8 static inite=\017#6==j; rrs char e1> static init("{016)">; f..'! ~ !!!.Q .i.e _11 Appearance: \023 Result: {002}J (Overstruck 3 js not part of escape sequence.> Appearance: 1112 Result: j 11 2 (Overstruck \ 1S not an escape character.> Appearance: a\##b Result: a\b (First # is not an erase character by rule 18; second # erases itself and preceding # by rule 14.> f!.g!!lgl~_l!t (similar to t:xample 13) Appearance: a\@#b Resul t: a\b MUlTICS TECHNICAL BULLETIN - 251 page 9 Appearance: aN@b Result: b (The \ is erased by the overstruck #.) Appearance: a\\#b Result: a\#b (Erase canonicalization do~s not recognize the # by rule 18; escape canonicalization recognizes \\ by rule 20, and attaches no special meaning to the #.> Appearance: a\\##b Result: a\b (8y rule 18, the first # is not an erase character; by rule 14, the second # erases itself and the preceding #; lbgD rule 20 reduces \\ to \.> Appearance: a\\###b Result: a\b (The first # is not an second \ and the first #.> erase; the next two are, erasing the MULTICS TECHNICAL BULLETIN - 251 pdgt:' 10 Appearance: a\\####b Result: ab (The first # is not an erase, and must be erased before the two \ characters. Examples 16-19 illustrate the difficulty of erasing a double \; the clearest method is probably to overstrike (aNNb).> f~~mu1f_2Q (on 2741-like terminal> Appearance: at<#b Result: a\b (Only the < is erased; t is translated to \.>
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