in reply to Re^4: Continuations in Perl - Returning to an arbitrary level up the call stack
in thread Continuations in Perl - Returning to an arbitrary level up the call stack

You are citing the POD, but I checked the source...

Cheers Rolf

( addicted to the Perl Programming Language)

  • Comment on Re^5: Continuations in Perl - Returning to an arbitrary level up the call stack

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Re^6: Continuations in Perl - Returning to an arbitrary level up the call stack
by vsespb (Chaplain) on May 19, 2013 at 00:00 UTC
    I've checked the source. Such things cannot be implemented with goto. And setjmp()/longjmp() is best explanation found in pod.
    Implementation done using eval EXPR (EXPR is a string) + goto RANDOM_label. Each time you call sub recursively - label is different!
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[d/l]
        Already demonstrated:
        No, this example is not about recursion (although there is some).
        Nope! Jump-labels only change each time with_return constructs are called to avoid confusion if they are dynamically nested.
        That's what I told - they change each time you _call_ with_return, not each time you have with_return in code.

        Here is example. Try do same with "goto"

        use strict;
use warnings;
use Return::MultiLevel qw/with_return/;
sub rec
{
        my ($i, $return) = (@_, undef);
        $i++;
        print "i=$i\n";
        if ($i == 3) {
                with_return {
                        my $newreturn = shift;
                        rec($i, $newreturn);
                };
        }
        if ($i == 5) {
                 $return->() if $return;
        }
        if ($i == 7) {
                return;
        }
        rec($i, $return);
}

rec(0);

__END__

$ perl ml.pl 
i=1
i=2
i=3
i=4
i=5
i=4
i=5
i=6
i=7

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