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resumable failures for coercions

fixes #17
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commit 5dfd99666bd8c05b7fc9de87d5c306c2399dfa08 1 parent 75e74e0
@TimToady TimToady authored
Showing with 12 additions and 3 deletions.
  1. +12 −3 S04-control.pod
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15 S04-control.pod
@@ -13,8 +13,8 @@ Synopsis 4: Blocks and Statements
Created: 19 Aug 2004
- Last Modified: 11 Mar 2012
- Version: 116
+ Last Modified: 28 Jul 2012
+ Version: 117
This document summarizes Apocalypse 4, which covers the block and
statement syntax of Perl.
@@ -1246,7 +1246,8 @@ lexical scope of the C<goto>) must enclose the label in quotes.
As in Perl 5, many built-in functions simply return an undefined value
when you ask for a value out of range, or the function fails somehow.
-Perl 6 has C<Failure> objects, known as "unthrown exceptions", which
+Perl 6 has C<Failure> objects, known as "unthrown exceptions" (though
+really a C<Failure> merely contains an unthrown exception), which
know whether they have been handled or not. C<$!> is a convenient
link to the last failure, and only ever contains one exception, the
most recent.
@@ -1308,6 +1309,14 @@ the implicit outermost exception handler will
eventually decide to abort and print all unhandled exceptions passed
in as its current C<@!> list.
+It is possible to fail with a resumable exception, such as a warning.
+If the failure throws its exception and the exception resumes,
+the thrower by default returns the null string (C<''>) to whatever
+caused the failure to throw its exception. This may be overridden by
+attaching a C<.resume_value> to the warning. Hence numeric coercions
+such as C<+"42foo"> can be forced to return C<42> after issuing
+a warning.
+
=head1 Phasers
A C<CATCH> block is just a trait of the closure containing it, and is
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