Author: larry Date: Tue Sep 12 11:07:01 2006 New Revision: 11969 Modified: doc/trunk/design/syn/S03.pod

Log: New X operator and metaoperator. Modified: doc/trunk/design/syn/S03.pod ============================================================================== --- doc/trunk/design/syn/S03.pod (original) +++ doc/trunk/design/syn/S03.pod Tue Sep 12 11:07:01 2006 @@ -14,7 +14,7 @@ Date: 8 Mar 2004 Last Modified: 12 Sep 2006 Number: 3 - Version: 58 + Version: 59 =head1 Changes to Perl 5 operators @@ -639,7 +639,7 @@ operators yourself. Similarly, the carets that exclude the endpoints on ranges are there by convention only. -In contrast to that, Perl 6 has four standard metaoperators for +In contrast to that, Perl 6 has five standard metaoperators for turning a given existing operator into a related operator that is more powerful (or at least differently powerful). These differ from a mere naming convention in that Perl automatically generates these new @@ -801,7 +801,7 @@ =head2 Reduction operators -The final metaoperator in Perl 6 is the reduction operator. Any +The fourth metaoperator in Perl 6 is the reduction operator. Any infix operator (except for non-associating operators) can be surrounded by square brackets in term position to create a list operator that reduces using that operation: @@ -1025,6 +1025,52 @@ mean the normal reduction of C<< infix:<\x> >> operator, not the triangular reduction of C<< infix:<x> >>. This is deemed to be an insignificant problem. +=head1 Cross operators + +The final metaoperator is the C<X> metaoperator. 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. + +The bare form of C<X> is considered an operator in its own right. +Saying: + + <a b> X 1,2 X <x y> + +produces + + ['a', 1, 'x'], + ['a', 1, 'y'], + ['a', 2, 'x'], + ['a', 2, 'y'], + ['b', 1, 'x'], + ['b', 1, 'y'], + ['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' + +Any existing, non-mutating infix operator may be used after the C<X>. + + 1,2 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 + +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' + =head1 Junctive operators C<|>, C<&>, and C<^> are no longer bitwise operators (see @@ -1401,6 +1447,18 @@ @foo := [[1,2,3],[4,5,6]]; say cat([;] @foo); # 1,2,3,4,5,6 +=head1 Crossing arrays + +In contrast to the zip operator, the C<X> operator returns all the +permutations of its sublists. Hence you may say: + + <a b> X <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. =head1 Minimal whitespace DWIMmery Whitespace is no longer allowed before the opening bracket of an array @@ -1481,7 +1539,7 @@ !!! ... ??? [+] [*] [<] [,] [\+] [\*] etc. (also = as list assignment) - list infix ¥ <== ==> + list infix ¥ <== ==> X X~ X* Xeqv etc. loose and and loose or or xor err expr terminator ; {} as control block, statement modifiers