Algol 68 - ACM Digital Library

180 van Wijngaarden, et al.10.3.4.1.2. Semantics{A format is brought into being by means of a format-text. A format isbest regarded as a tree, with a collection at each node and a picture ateach tip. In order to avoid violation of the scope restrictions, each node ofthis tree is, in this Report, packed into a value of mode "PIECE'. A formatis composed of a row of such pieces and the pieces contain pointers toeach other in the form of indices selecting from that row. An implementerwill doubtless store the tree in a more efficient manner. This is possiblebecause the field.selector of a format is hidden from the user in order thathe may not break it open.Although a format-text may contain ENCLOSED-clauses (in replicatorsand format-patterns) or units (in general-patterns), these are notelaborated at this stage but are, rather, turned into routines forsubsequent calling as and when they are encountered during formattedtransput. Indeed, the elaboration of a format-text does not result in anyactions of any significance to the user.}a) The yield of a format-text F, in an environ E, is a structured valuewhose only field is a multiple value W, whose mode is "row of PIECE',composed of a descriptor ((1, n)) and n elements determined as follows:• a counter i is set to 1;• F is "transformed" {b} in E into W, using i.b) A format-text or a collection-list-pack C is "transformed" in anenviron E into a multiple value W whose mode is "row of PIECE', using acounter i, as follows:• the element of W selected by (i) is a structured value, whose mode is'PIECE' and whose fields, taken in order, are• {cp} undefined;• {count} undefined;• {bp} undefined;• {c} a multiple value V, whose mode is "row of COLLECTION', havinga descriptor ((1, m)), where m is the number of constituent collectionsof C, and elements determined as follows:For j = 1 ..... m, letting C. be the j-th constituent collection of C,ICase A: The direct descendents of C. include a picture P:J• the constituent pattern T, if any, and the insertion I of P areelaborated collaterally;• the j-th element of V is a structured value, whose mode is'PICTURE' and whose fields, taken in order, are• [p} the yield of T, if any, {e, 10.3.4.8.2, 10.3.4.9.2, 10.3.4.10.2}and, otherwise, empty;• (i} the yield of ! {d};/ALGOL 68 Revised Report 181Case B: The direct descendents of C. include a first insertion I1, aJreplicator REP, a collection-list-pack P and a second insertion 12:• i is increased by 1;• I1, REP and 12 are elaborated collaterally;• the j-th element of Y is a structured value whose mode is'COLLITEM' and whose fields, taken in order, are• {il} the yield of I1 {d};• {rep} the yield of REP {c};• (Pli;• (i2] the yield of 12;• P is transformed in E into W, using i.c) The yield, in an environ E, of a NEST-UNSUPPRESSETY-replicatorR {10.3.4.1.l.g,h} is a routine whose mode is 'procedure yielding integral',composed of a proeedure-yielding-integrai-NEST-routine-text whose unit isU, together with the environ necessary {7.2.2.c} for U in E, where U isdetermined as follows:Case A: R contains a meek-integral-ENCLOSED-clause G:• O is a new unit akin {1.1.3.2.k} to C;Case B: R contains a fixed-point-numeral D, but no ENCLOSED-clause:• U is a new unit akin to D;Case C: R is invisible:• U is a new unit akin to a fixed.point-numeral which has an intrinsicvalue {8.1.1.2} of 1.d) The yield of an insertion I {10.3.4.1.1.d} is a multiple value Wwhose mode is 'INSERTION', determined as follows:* let U 1 ..... U n be the constituent UNSUPPRESSETY-replieators of I,and let A i, i = 1 ..... n, be the denoter-coercee or alignment-code{immediately} following U.;• let R 1, .... R and O 1 ... D be the {collateral} yields of U 1, On ' ' n .... nand A 1 ..... A n, where the yield of an alignment-code is the {characterwhich is the} intrinsic value {8.1.4.2.b} of its LETTER-symbol;• the descriptor of W is ((1, n)):• the element of W selected by (i), i = 1 ..... n, is a structured value {ofthe mode specified by struct .(proc lnt rep, union (string, char) sa)} whosefields, taken in order, are• {rep} R.;I• {sa} D..Ie) The yield of an integral-, real-, boolean-, complex-, string: or bitspatternP {10.3.4.2.1.a, 10.3.4.3.1.a ..... t0.3.4.7.l.a} is a structured value Wwhose mode is 'PATTERN', determined as follows: