Author: lwall
Date: 2010-03-16 01:14:25 +0100 (Tue, 16 Mar 2010)
New Revision: 30095
Modified:
docs/Perl6/Spec/S03-operators.pod
Log:
[S03] take conservative approach to differing X or Z metaops for now
Modified: docs/Perl6/Spec/S03-operators.pod
===================================================================
--- docs/Perl6/Spec/S03-operators.pod 2010-03-15 23:10:23 UTC (rev 30094)
+++ docs/Perl6/Spec/S03-operators.pod 2010-03-16 00:14:25 UTC (rev 30095)
@@ -16,7 +16,7 @@
Created: 8 Mar 2004
Last Modified: 15 Mar 2010
- Version: 197
+ Version: 198
=head1 Overview
@@ -4418,16 +4418,20 @@
(<a b>; 1,2).cross.slice.map { .reduce(&[~]) }
-And
+Note that
<a b> X~ 1,2 X+ 3,4
-might mean
+could mean something like
- (<a b>; 1,2; 3,4).cross.slice.map { .reduce(&[~],&[+]) }
+ (<a b>; 1,2; 3,4).cross.slice.map { .reduce({$^a ~ $^b + $^c}) }
-(But see below.)
+but it is currently illegal as a non-identical list associative
+operator, which is considered non-associative. You can, however,
+always use parens to be explicit:
+ <a b> X~ (1,2 X+ 3,4)
+
The list concatenating form, C<X,>, when used like this:
<a b> X, 1,2 X, <x y>
@@ -4490,17 +4494,21 @@
(<a b>; 1,2).zip.slice.map { .reduce(&[~]) }
-And
+Note that
- <a b> Z~ 1,2 Z+ 3,4 # 'a4', 'b6'
+ <a b> Z~ 1,2 Z+ 3,4
-would mean
+could mean something like
- (<a b>; 1,2; 3,4).zip.slice.map { .reduce(&[~],&[+]) }
+ (<a b>; 1,2; 3,4).zip.slice.map { .reduce({$^a ~ $^b + $^c}) }
-implying that multi-function reduce knows how to compare the precedence
-of its operator arguments somehow. That seems unreasonable. The clean
-way to solve this might involve giving C<X> and C<Z> metaoperators a
+but it is currently illegal as a non-identical list associative
+operator, which is considered non-associative. You can, however,
+always use parens to be explicit:
+
+ <a b> Z~ (1,2 Z+ 3,4)
+
+[Conjecture: another approach would involve giving C<X> and C<Z> metaoperators
a
subprecedence within listop precedence corresponding to the original
operator's precedence, so that C<Z~> and C<Z+> actually have different
precedences within listop precedence. Then the above would parse as if
@@ -4508,7 +4516,7 @@
parse at list infix precedence, with comma tighter than the zips.
(This would actually be fairly trivial to implement, given how we
represent our precedence as strings.) Also, though it's complicated to
-explain, subprecedence within C<Z> might be exactly what the naive user
expects.
+explain, subprecedence within C<Z> might be exactly what the naive user
expects.]
The list concatenating form, C<Z,>, when used like this:
