Author: larry Date: Tue Sep 12 21:09:33 2006 New Revision: 11975 Modified: doc/trunk/design/syn/S03.pod

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Log: tweaks to crossop syntax Modified: doc/trunk/design/syn/S03.pod ============================================================================== --- doc/trunk/design/syn/S03.pod (original) +++ doc/trunk/design/syn/S03.pod Tue Sep 12 21:09:33 2006 @@ -1031,14 +1031,22 @@ =head1 Cross operators -The final metaoperator is the C<X> metaoperator. It applies the +The final metaoperator is the cross metaoperator. It is formed syntactically +by placing an infix operator between two C<X> characters. It applies the modified operator across all permutations of its list arguments. All -C<X> operators are of list infix precedence, and are list associative. +cross operators are of list infix precedence, and are list associative. -The bare form of C<X> is considered an operator in its own right. -Saying: +The string concatenating form is: + + <a b> X~X <1 2> # 'a1', 'a2', 'b1', 'b2' + +The C<X~X> operator desugars to something like: + + [~]«( <a b> X <1 2> ) # 'a1', 'a2', 'b1', 'b2' - <a b> X 1,2 X <x y> +The list concatenating form + + <a b> X,X 1,2 X,X <x y> produces @@ -1051,33 +1059,25 @@ ['b', 2, 'x'], ['b', 2, 'y'] -The string concatenating form is: - - <a b> X~ <1 2> # 'a1', 'a2', 'b1', 'b2' - -As a metaoperator, C<X~> operator desugars to something like: - - [~]«( <a b> X <1 2> ) # 'a1', 'a2', 'b1', 'b2' +The string and list forms are common enough to have shortcuts, C<X> +and C<XX> respectively. See below. -Any existing, non-mutating infix operator may be used after the C<X>. +For the general form, any existing, non-mutating infix operator +may be used. - 1,2 X* 3,4 # 3,4,6,8 + 1,2 X*X 3,4 # 3,4,6,8 (Note that C<< <== >> and C<< ==> >> are considered mutating, as well as all assignment operators.) If the underlying operator is non-associating, so is the metaoperator: - @a Xcmp @b Xcmp @c # ILLEGAL - @a Xeq @b Xeq @c # ok + @a XcmpX @b XcmpX @c # ILLEGAL + @a XeqX @b XeqX @c # ok In fact, though the C<X> operators are all list associative syntactically, the underlying operator is always applied with its -own associativity. - -Unlike bare C<X>, the C<X,> form flattens much like C<[,]> does. - - <a b> X, <1 2> # 'a', '1', 'a', '2', 'b', '1', 'b', '2' +own associativity, just as the corresponding reduce operator would do. Note that only the first term of an C<X> operator may reasonably be an infinite list. @@ -1460,16 +1460,24 @@ =head1 Crossing arrays -In contrast to the zip operator, the C<X> operator returns all the +In contrast to the zip operator, the C<XX> operator returns all the permutations of its sublists. Hence you may say: - <a b> X <1 2> + <a b> XX <1 2> and you end up with ['a', '1'], ['a', '2'], ['b', '1'], ['b', '2'] -It is really a variant of the C<X> metaoperator mentioned earlier. +The C<X> variant crosses the arrays but concatenates strings: + + <a b> X <1 2> + +produces + + 'a1', 'a2', 'b1', 'b2' + +The resemblance to C<x> and C<xx> is not entirely accidental. =head1 Minimal whitespace DWIMmery @@ -1551,7 +1559,7 @@ !!! ... ??? [+] [*] [<] [,] [\+] [\*] etc. (also = as list assignment) - list infix ¥ <== ==> X X~ X* Xeqv etc. + list infix ¥ <== ==> X XX X~X X*X XeqvX etc. loose and and loose or or xor err expr terminator ; {} as control block, statement modifiers