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