Algol 68 - ACM Digital Library

126 van Wijngaarden, et al.b) The constituent standard-prelude of all program-texts is thatstandard-prelude whose representation is obtained {10.1.3} from the formsgiven in sections 10.2 and 10.3.c) The constituent library-prelude of a program-text is not specified inthis Report {but must be specified for each implementation: the syntax of"program text' ensures that a declaration contained in a library-preludemay not contradict any declaration contained in the standard-prelude}.d) The constituent system-prelude (system-task-list) of all programtextsis that system-prelude (system-task-list) whose representation isobtained from the forms given in section 10.4, with the possible addition ofother forms not specified in this Report {but to be specified to suit theoperating environTmnt of each implementation}.JLe) Each constituent particular-prelude (particular-postlude) of allprogram-texts is that particular-prelude (particular-postlude) whoserepresentation is obtained from the forms given in section 10.5, with thepossible addition of other forms not specified in this Report {but to bespecified for each implementation}.10.1.3. The method of description of the standard environmentA representation of an EXTERNAI,-prelude, system-task or particularpostludeis obtained by altering each form in the relevant sections of thischapter in the following steps:Step 1: If a given form F begins with op {the operator-symbol} followed byone of the marks P, Q, R or E, then F is replaced by a number of newforms each of which is a copy of F in which that mark {following theop} is (all other occurrences in F of that mark are) replaced, in eachrespective new form, by:Case A: The mark is P:• -, +, '~x,,:~ or I(-, +, x or/);Case B: The mark is Q:• ~minusab, -:=~, 1tplusab, +:=~, ~timesab, x:=,,: =~" ordivab, / : =(-:=, +:=, x:= or/:=):Case C: The mark is R:• ~=, ge~, or~>, gt~();Case D: The mark is E:• ~L=,eq~ or ~,/=,ne~(= or ~):Step 2: If, in some form, as possibly made in the step above, .~ occursfollowed by an INDICATOR (a field-selector) I, then that occurrence ofALGOL 68 Revised Report 127.~ is deleted and each INDICATOR (field-selector) akin {1.1.3.2.k} to Icontained in any form is replaced by a copy of one same INDICATOR(field-selector) which does not occur elsewhere in the program andStep 2 is taken again;Step 3: If a given form F, as possibly modified or made in the steps above,beg!ns with op {the operator-symbol} followed by a chain of TAOsymbolsseparated by and-also-symbols, the chain being enclosedbetween ~ and ~., then F is replaced by a number of different"versions" of that form each of which is a copy of F in which thatchain, together with its enclosing ¢ and t", has been replaced by one ofthose TAO-symbois {; however, an implementation is not, obliged toprovide more than one such version (9.4.b)};Step 4: If, in a given form, as possibly modified or made in the stepsabove, there occurs a sequence S of symbols enclosed between ~ andand if, in that S, L int,~L real, L compl, /L bits or L bytes occurs, then Sis replaced by a chain of a sufficient number of sequences separated byand-also-symbols, the n-th of which is a copy of S in which copy eachoccurrence of L (L, K, 8) is replaced by (n - 1) times long (long, leng,shorten), followed by an and.also-symbol and a further chain of asufficient number of sequences separated by and-also-symbols, the m-thof which is a copy of S in which copy each occurrence of L (L, K, S)has been replaced by m times short (short shorten, leng): the ~ andenclosing that S are then deleted;Step 5: If, in a given form F, as possibly modified or made in the stepsabove, Lint (L real, L compl, L bits, L bytes) occurs, then F isreplaced by a sequence of a sufficient number of new forms, the n-th ofwhich is a copy of F in which copy each occurrence of L (L, K, S) isreplaced by (n- 1) times long (long, leng, shorten), and eachoccurrence of Iong L (long L) by n times long (long), followed by afurther sequence of a sufficient number of new forms, the m-th ofwhich is a copy of F in which copy each occurrence of L (L, K, S) isreplaced by m times short (short, shorten, leng), and each occurrenceof IongL (longL) by (m - 1) times short (short); ]Step 6: Each occurrence of F (PRIM) in any form, as possibly modifiedor made in the steps above, is replaced by a representation of a letter.aleph-symbol (primal-symbol) {9.4.a};Step 7: If a sequence of representations beginning with and ending with ¢occurs in any form, as possibly modified or made in the steps above,then this sequence, which is termed a "pseudo-comment", is replacedby a representation of a declarer or closed-clause suggested by thesequence;