Try this... 
my %cache;
while($foo < (exists $cache{$bar} ? $cache{$bar} : 
      $cache{$bar} = &ReallyComplexFunction($bar))) {
  doStuff();
}

[download]
Untested, but should work

Update I just realized how funny $cache{$bar} is, if cache is pronounced correctly ;)

Update2 Also remembered that there is a module to do this... Memoize

                - Ant
                - Some of my best work - Fish Dinner

In reply to Re: Efficiency and Functions in loops by suaveant
in thread Efficiency and Functions in loops by Superlman

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