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42 van Wijngaarden, et al.d) If N is a stowed name referring to a structured (multiple) value Y[2.1.3.3, 2.1.3.4}, and if a subname {2.1.2.g] of N selected {2.1.3.3.e, 2.1.3.4.g}by a 'TAG' (an index) I is made to refer to a {new} value X, then N ismade to refer to a structured (multiple) value which is the same as Yexcept for its field (element) selected by I, which is {now made to be} ×.{For the mode of a subname, see 2.1.3.3.d and 2.1.3.4.f.}2.1.3.3. Structured valuesa) A "structured value" is composed of a sequence of other values, its"fields", each of which is "selected" [b} by a specific "TAG" {9.4.2.1.A}. {Forthe selection of a field by a field-selector, see 2.1.5.g.}{The ordering of the fields of a structured value is utilized in thesemantics of structure.displays (3.3.2.b) and format-texts (10.3.4), and instraightening (10.3.2.3.c).}b) The mode of a structured value V is some 'structured with FIEIJ)Smode'. If the n-th "FIELD' enveloped by that 'FIELDS' is some 'MODE fieldTAG', then the n-th field of Y is "selected" by "TAG" and is acceptable to{2.1.3.6.d} "MODE'.c) The scope of a structured value is the newest of the scopes of itsfields.d) If the mode of a name N {referring to a structured value} is some'reference to structured with FIELDS mode', and if the predicate "whereMODE field TAG resides in FIELDS' holds {7.2.1.b,c}, then the mode of thesubname of N selected {e} by "TAG' is 'reference to MODE'.e) When a name N which refers to a structured value V is "endowedwith subnames" {e, 2.1.3.4.g, 4.4.2.b, 5.2.3.2.a}, then,For each 'TAG' selecting a field F in V,• a new subname M is created of the same scope as N:• M is made to refer to F;• M is said to be the name "selected" by "TAG" in N:• if M is a stowed name {2.1.3.2.b}, then it is itself endowed withsubnames {e, 2.1.3.4.g}.2.1.3.4. Multiple valuesa) A "multiple value" {of n dimensions} is composed of a "descriptor"and a sequence of other values, its "elements", each of which may be"selected" by a specific n-tuple of integers, its "index".b) The "descriptor" is of the form((I 1, Ul),(I 2, u 2) .....(I n , Un))where each (li, ui) , i = 1 ..... n, is a "bound pair" of integers in which I. isIthe i-th "lower bound" and u. is the i-th "upper bound".IALGOL <strong>68</strong> Revised Report 43C) If for any i, i=1 ..... n, u i < li, then the descriptor is said to be"flat" and there is one element, termed a "ghost element" {, and notselected by any index; see also 5.2.1.2.b}; otherwise, the number ofelements is (u 1 -I 1+ 1) x (u 2-12+ 1) x ... x (u n -I + 1) and each isnselected by a specific index (r 1 ..... r n) where I.i
44 van Wijngaarden, et al.h) A "trim" is an n-tuple, each element of which is either an integer{corresponding to a subscript} or a triplet (I, u, d) {corresponding to atrimmer or a revised.lower-bound-option}, such that at least one of thoseelements is a triplet {if all the elements are integers, then the n-tuple is anindex (a)}. Each element of such a triplet is either an integer or is"absent".{A trim (or an index) is yielded by the elaboration of an indexer(5.3.2.2.b) .}i) The multiple value W {of m dimensions} "selected" by a trim T in amultiple value V {of n dimensions, 1
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