Algol 68 - ACM Digital Library

56 van Wijngaarden, et al.3.2.2. Semanticsa) The yield of a serial-clause, in an environ E, is the yield of theelaboration of its series, or of any series elaborated "in its place" {5.4.4.2},in the environ "established" {b} around E according to that serial-clause; itis required that the yield be not newer in scope than E.b) The environ E "established"• upon an environ El, possibly not specified, {which determines itsscope,}• around an environ E2 {which determines its composition},• according to a NOTlON-defining-new-PROPSETY C, possibly absent,{which prescribes its locale,}• with values Y 1 ..... Y n, possibly absent, {which are possibly to beascribed,}is determined as follows:• if E1 is not specified, then let E1 be E2:• E is newer in scope than E1 and is composed of E2 and a new localecorresponding to 'PROPSETY', if C is present, and to 'EMPTY' otherwise;Case A: C is an establishing-clause:For each constituent mode-definition hi, if any, of C,• the scene composed of(i) the actual-declarer of M, and(ii) the environ necessary for {7.2.2.c} that actual-declarer in E,is ascribed in E to the mode-indication of M:For each constituent label.definition L, if any, of C,• the scene composed of(i) the series of which L is a direct descendent, and(ii) the environ E,is ascribed in E to the label-identifier of L:If each 'PROP' enveloped by 'PROPSETY' is some "DYADIC TAD" or'label TAG',then E is said to be "nonlocal" {see 5.2.3.2.b};Case B: G is a declarative, a for-part or a specification:For i= 1 ..... n, where n is the number of 'DEC's enveloped by'PROPSETY',• Y. is ascribed {4.8.2.a} in E to the i-th constituent defining-Iidentifier, if any, of G and, otherwise {in the case of an invisible forpart},to an integral-defining-indicator.with-letter-aleph;If C is a for-part or a specification,then E is nonlocal.{Other cases, i.e., when C is absent:• E is local (see 5.2.3.2.b), but not further defined.}c) The yield W of a series C is determined as follows:If C contains a direct descendent unit which is not followed by a go-ontoken,ALGOL 68 Revised Reportthen• W is the yield of that unit;otherwise,• the declaration or the unit, if any, of C is elaborated;• W is the yield of the series of C.{See also 5.4.4.2.Case A.}3.3. Collateral and parallel clauses{Collateral-clauses allow an arbitrary merging of streams of actions.Parallel.clauses provide, moreover, levels of coordination for thesynchronization (10.2.4) of that merging.A collateral- or parallel-clause consists of a sequence of units separatedby and-also-symbols (viz., ","), and is enclosed by parentheses or by abegin-end pair; a parallel-clause begins moreover with par.Collateral-clauses, but not parallel-clauses, may yield stowed valuescomposed from the yields of the constituent units.Examples of collateral.clauses yielding stowed values:[ ] int q = (1, 4, 9, 16, 25);struct (int price, string category) bike := (150, "sport").Example of a parallel-clause which synchronizes eating and speaking:pro¢ void eat, speak; soma mouth = level 1;par begindodown mouth;eat;up mouthod,dodown mouth;speak;up mouthodend .}3.3.1. Syntaxa) strong void NEST collateral clause{5D,551a} :strong void NEST joined portrait{b} PACK.b) SOlD NEST joined portrait{a,b,c,d,34g} :where SOlD balances SOIDI and SOlD2{32e},SOIDI NEST unit{32d}, and also{94f} token,SOLD2 NEST unit{32d}or alternatively SOLD2 NEST joined portrait{b}.c) strong void NEST parallel clause{5D,551a} :parallel{94f} token, strong void NEST joined portrait{b} PACK.d) strong ROWS of MODE NEST collateral clause{5D,551a} :where (ROWS) is (row),strong MODE NEST joined portrait{b} PACK ;57