in reply to Unusual Closure Behaviour
(tachyon asks about my $x if undef.)
This was discussed extensively on p5p about a year ago. The end result of the discussion is that this behavior is a bug, and, although it is going to stay in for the time being because nobody can see how to fix it, you should not depend on it either, because it is a bug, and someone might even fix it someday.
The thread begins here, and there is a recent message about it from Jarkko Hietaniemi that calls it a bug, and an older message from Larry Wall that says In Ada parlance, use of this feature would be considered erroneous.
In Section
Seekers of Perl Wisdom