Author: lwall
Date: 2010-02-24 19:11:54 +0100 (Wed, 24 Feb 2010)
New Revision: 29827
Modified:
docs/Perl6/Spec/S29-functions.pod
Log:
[S29] restrict Matcher from taking Bool
Modified: docs/Perl6/Spec/S29-functions.pod
===================================================================
--- docs/Perl6/Spec/S29-functions.pod 2010-02-24 18:10:51 UTC (rev 29826)
+++ docs/Perl6/Spec/S29-functions.pod 2010-02-24 18:11:54 UTC (rev 29827)
@@ -20,8 +20,8 @@
Created: 12 Mar 2005
- Last Modified: 2 Feb 2010
- Version: 45
+ Last Modified: 24 Feb 2010
+ Version: 46
The document is a draft.
@@ -117,10 +117,18 @@
=item Matcher
- subset Matcher of Object where { $_.can('ACCEPTS') };
+ subset Matcher of Mu where none(Bool)
Used to supply a test to match against. Assume C<~~> will be used against it.
+Booleans are forbidden because they almost always indicate a programming
+error where the argument has been evaluated too soon against the wrong C<$_>.
+For instance:
+ grep $_ == 1, 1,2,3; # evaluating wrong $_, so forbidden
+ grep { $_ == 1 }, 1,2,3; # okay
+ grep * == 1, 1,2,3; # okay
+
+
=item Ordering
subset KeyExtractor of Code where { .signature === :(Any --> Any) };
@@ -1006,4 +1014,4 @@
Please post errors and feedback to perl6-language. If you are making
a general laundry list, please separate messages by topic.
-
+=for vim:set expandtab sw=4:
