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
