Algol 68 - ACM Digital Library

184 van Wijngaarden, et al.{Examples:a) +zd.lld • +.12de+2d b) zd.lld • .12dc) .12de+2d }{For the semantics of real-patterns see 10.3.4.1.2.e.}{aa) The modes which are output (input) compatible with a 'real'pattern are those specified by L real and Lint (by refL real).bb) A value V is converted to a string S using a 'real' pattern P asfollows:• if P contains a sign mould, then the first character of S is the sign of V;otherwise, if Y < 0, the conversion is unsuccessful;• the remainder of S contains a decimal representation of V determinedas follows:• if necessary, V is widened to a real number;• the element of S controlled by the "." Ce") frame, if any, of P is "."("lo")"If P contains an "e" frame,then• let W be the sequence of frames preceding, and IP be the'integral' pattern following, that "e" frame:• an exponent E is calculated by standardizing V to the largestvalue convertible using W (see below):• the part of S controlled by IP is obtained by converting E usingIP (see 10.3.4.2.1.bb):otherwise,• let W be the whole of P:• the elements of S controlled by the "d" and "z" frames of W are theappropriate digits (thus the pattern specifies the number of digits to beused, and the number of digits to be placed after the decimal point, ifany);• if V cannot be represented by such a string, the conversion isunsuccessful.cc) A string S is converted to a real number suitable for a name N,using a "real" pattern, as follows:• the real number R for which S contains a decimal representation isconsidered:• if R is greater than the largest value to which N can refer, theconversion is unsuccessful: otherwise, R is the required real number.}10.3.4.4. Boolean patterns10.3.4.4.1. Syntaxa) NEST boolean pattern{A341c} :NEST unsuppressible boolean frame{A341j}.b) boolean marker{A341j,A348b} : letter b{94a} symbol.{Example:a) 14x b }ALGOL 68 Revised Report 185{For the semantics of boolean-patterns see 10.3.4.1.2.e.}{aa) The mode which is output (input) compatible with a "boolean'pattern is that specified by bool (refbool).bb) A value Y is converted to a string using a 'boolean" pattern asfollows:• if Y is true (false), then the string is that yielded by flip (flop).co) A string S is converted to a boolean value, using a "boolean'pattern, as follows:• if S is the same as the string yielded by flip (flop), then the requiredvalue is true (false).}10.3.4.5. Complex patterns10.3.4.5.1. Syntaxa)b){Example:NEST complex pattern{A341c} : NEST real pattern{A343a},NEST complex frame{A341j}, NEST real pattern{A343a}.complex marker{A341j} : letter i{94a} symbol.a) +.12de+2d 3q"+jx"3"." si +.lOde+2d }{For the semantics of complex-patterns see 10.3.4.1.2.e.}{aa) The modes which are output (input) compatible with a 'complex'pattern are those specified by L compl, L real and Lint (by ref L compl).bb) A value V is converted to a string S using a "eomplex' pattern Pas follows: I• if necessary, V is widened to a complex number;• the element of S controlled by the "i" frame of P is ".1_":• the part of S controlled by the first (seeond) "real" pattern of P is thatobtained by converting the first (second) field of V to a string using thefirst (second) 'real' pattern of P (10.3.4.3.!1.bb); /• if either conversion is unsuccessful, the conversion of V is unsuccessful.cc) A string is converted to a complex value C suitable for a name N,using a 'complex' pattern P, as follows:• the part of the string controlled by the first (second) 'real" pattern of Pis converted to a suitable real number ii0.3.,~.3./1.ec)~,)which then forms thefirst (second) field of C; - i - .• if either conversion is unsuccessful, the conversion to C is unsuccessful.}f