BrowserUk,
I am not sure I agree. The user defined sub is getting called in both cases as a comparator and there doesn't appear to be any ambiguity. By putting a print statement inside the sub, I can count how many times it is called. 52 for the working version and 2 for the b0rk version before it blows up.

Now here is where it gets interesting, if I include $a and $b in the print statement I discover that in the first call both variables are set to two different array refs (as expected). On the second call (the one that blows up), neither variable is defined??? 

sub my_sort {
    print "hello there $a $b\n";
    my $i = $_[0] || 0;
    ...
}
__END__
hello there ARRAY(0x1868244) ARRAY(0x1868298)
Use of uninitialized value in concatenation (.) or string at ...
Use of uninitialized value in concatenation (.) or string at ...
hello there

*** BOOOOM ***

[download]

Cheers - L~R

In reply to Re^4: Sorting, recursion, and tail-call optimizations by Limbic~Region
in thread Sorting, recursion, and tail-call optimizations by Limbic~Region

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