Author: larry Date: Sun Oct 8 22:34:45 2006 New Revision: 12874 Modified: doc/trunk/design/syn/S04.pod
Log: Ordinary undef is not an undefined generator, only unthrown exceptions are. Modified: doc/trunk/design/syn/S04.pod ============================================================================== --- doc/trunk/design/syn/S04.pod (original) +++ doc/trunk/design/syn/S04.pod Sun Oct 8 22:34:45 2006 @@ -12,9 +12,9 @@ Maintainer: Larry Wall <[EMAIL PROTECTED]> Date: 19 Aug 2004 - Last Modified: 5 Oct 2006 + Last Modified: 8 Oct 2006 Number: 4 - Version: 42 + Version: 43 This document summarizes Apocalypse 4, which covers the block and statement syntax of Perl. @@ -928,20 +928,19 @@ to false in a boolean context.) A list can have a defined length even if it contains undefined scalar values. A list is of undefined length only if it contains an undefined generator, which, happily, is -what is returned by the C<undef> function when used in list context. +what is returned by the C<fail> function when used in list context. So any Perl 6 function can say - return undef; + fail "message"; and not care about whether the function is being called in scalar or list context. To return an explicit scalar undef, you can always say - return item(undef); + return undef; Then in list context, you're returning a list of length 1, which is defined (much like in Perl 5). But generally you should be using -C<fail> in such a case to return an exception object. Exception -objects also behave like undefined generators in list context. +C<fail> in such a case to return an exception object. In any case, returning an unthrown exception is considered failure from the standpoint of C<let>. Backtracking over a closure in a regex is also considered failure of the closure, which is how hypothetical
