I recently started reading A Field Guide to Genetic Programming ... Barely in to it at all yet, but I've decided to rewrite the sample code (TinyGP) in Ruby. Because I like Ruby better than Java.
It's very short. And the (very rough) ruby implementation w/o much anything special done to it is quite a bit shorter – down from 12KB to 8, and I really didn't take anything out. That's just the extra cruft that Java requires. For all I know the ruby implementation is orders of magnitude slower, though, I don't know. Hell, I've barely tested it so I don't even know it works.
The code's @ github.