Try the following. It runs - I don't know if it works. 
sub greedy_change {
    my $change = shift;
    my $coin_count = 0;
    my @combo;
    my $blah = sub {
                print "Code doesn't get run after once.\n";
                my @lengths = ($_[1]);
                my $new_count = 0;
                $lengths[$_] = $_[$_+1] - $_[$_] for 1..$#denoms;
                $new_count += $lengths[$_]/$denoms[$_] for 0..$#denoms
+;
                if (!$coin_count or $new_count < $coin_count) {
                    print "$change: $new_count is better than $coin_co
+unt\n";
                    $coin_count = $new_count;
                    @combo = @lengths;
                }
    };

    print "Trying to change $change with @denoms...\n";
    print "$expr on $_\n";

    $_ = ('1' x $change);
    if (
        m{^$expr$
            (?{ $blah->(@+) })
        }x)
    {
        print "Matched!\n";
    }
    if ($coin_count) {
        print "C=$coin_count\n";
    }
    else {
        print "No matching combination found\n";
    }
    @combo;
}

[download]

It looks like there's some re-entrancy issues. The ARRAY ref thingy is because @_ is borked. If you put a print "@_\n"; as the first line, you'll get the same thing. If you put a print "Hello\n"; as the first line, you'll get a Signal 1 error (whatever that is).

Either way, you've found a bug in Perl. I would guess it's in the experimental use re 'eval'; feature you're (ab)using.

Being right, does not endow the right to be rude; politeness costs nothing.
Being unknowing, is not the same as being stupid.
Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.

In reply to Re: Undefined value as array reference by dragonchild
in thread Undefined value as array reference by Roy Johnson

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