while (my $item = shift @toprocess)

[download]

will fail if one of the items evaluates to false. You want to check "if an item has been returned", not "if an item has been returned and its true". Fix: 

while (my ($item) = shift @toprocess)

[download]

A list assignment in scalar context returns the number of items being assigned.

Update: Oops, I'm used to dealing with iterators that return () when out of data. As per tye's reply, my fix makes things worse. The following allows false values without introducing an infinite loop: 

while (@toprocess) {
   my $item = shift @toprocess;

[download]

Due to the extra complexity, it might make more sense to the simpler original if it's safe.

In reply to Re^2: Unshift and push inside of map operation. by ikegami
in thread Unshift and push inside of map operation. by LNEDAD

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