How fitting that a discussion about recursion gets to over 12 levels of depth! ;-)

I will see your 13, and take it one more level down ;- )

The problem I have had in some cases, though, is that perl starts to complain about deep recursion when I try recursive algorithms that go just one or two thousand levels down...

FWIK, Perl's deep recursion error is a somewhat arbitrary number (I think its actually set to 1000), and has no real bearing on perl's ability to keep recursing (which is only limited to the physical resources (memory/CPU/disk-swap) available for it to consume). And I believe that someone once told me you can easily change that number and recomplile perl if you need more.