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Re^2: Misunderstanding Recursion

by ikegami (Patriarch)
on Dec 16, 2006 at 00:29 UTC ( [id://590164]=note: print w/replies, xml ) Need Help??


in reply to Re: Misunderstanding Recursion
in thread Misunderstanding Recursion

The multiplication happens after the recursive call in your snippet, so your snippet isn't tail recursive. The following is a tail recursive version of your snippet:

sub _tail_recur { my ($x, $y) = @_; if ($x <= 1) { return $y; } else { return _tail_recur($x - 1, $x * $y); } } sub tail_recur { my ($x) = @_; return _tail_recur($x, 1); }

Tail recursion allows for the compiler to automatically flatten recursion (slow, and memory usage is proportional to the recursion depth) into a loop (fast, and memory usage is constant). Unfortunately, Perl5 does not do tail-recursion optimization.

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