I found this page with the function to do so: http://terpstra.ca/compare.html

I also found this thread: http://bumppo.net/lists/fun-with-perl/1999/09/msg00000.html which discusses how to do this with some canonical formed expressions. 

A function like this would really be able to speed some applications up, which matches a lot of strings with a number of expressions. If you know which ones are disjoint, you can break the test when one test matches.