Author: lwall
Date: 2010-05-26 19:21:03 +0200 (Wed, 26 May 2010)
New Revision: 30812
Modified:
docs/Perl6/Spec/S03-operators.pod
Log:
[S03] explain how not-raising works on != and ne
Modified: docs/Perl6/Spec/S03-operators.pod
===================================================================
--- docs/Perl6/Spec/S03-operators.pod 2010-05-26 16:55:57 UTC (rev 30811)
+++ docs/Perl6/Spec/S03-operators.pod 2010-05-26 17:21:03 UTC (rev 30812)
@@ -15,8 +15,8 @@
Created: 8 Mar 2004
- Last Modified: 21 May 2010
- Version: 205
+ Last Modified: 26 May 2010
+ Version: 206
=head1 Overview
@@ -3118,22 +3118,29 @@
successful thread may terminate the other threads abruptly. In general
you probably want to avoid code with side effects in junctions.
-Use of negative operators with syntactically recognizable junctions may
-produce a warning on code that works differently in English than in Perl.
-Instead of writing
+Use of negative operators with junctions is potentially problematic if
+auththreaded naively. However, by defining C<!=> and C<ne> in terms
+of the negation metaoperator, we automatically get the "not raising"
+that is expected by an English speaker. That is
if $a != 1 | 2 | 3 {...}
-you need to write
+really means
- if not $a == 1 | 2 | 3 {...}
+ if $a ![==] 1 | 2 | 3 {...}
-However, this is only a syntactic warning, and
+which the metaoperator rewrites to a higher-order function resembling
+something like:
- if $a != $b {...}
+ negate((* == *), $a, (1|2|3));
-will not complain if $b happens to contain a junction at runtime.
+which ends up being equivalent to:
+ if not $a == 1 | 2 | 3 {...}
+
+which is the semantics an English speaker expects. However, it may well
+be better style to write the latter form yourself.
+
Junctive methods on arrays, lists, and sets work just like the
corresponding list operators. However, junctive methods on a hash
make a junction of only the hash's keys. Use the listop form (or an
