BTW, as far as not calling recursive (or otherwise very expensive) functions more then neccessary, if you do this a lot, consider Memoize, which is designed for exactly that. It's not quite as transparent with objects as it is with, say, factorial, but if your code has a lot of redundant calls it's certianly worth the effort.

You might want to read The Perl Hardware Store section on Memoization and Quantitative Analysis of Memoization, both talks by Mark-Jason Dominous, the author of Memoize. (For that matter, his entire site is full of mind-bending perl stuff.)

Update:Memoize, not Memonize, thanks mirod.