Radix trees for Common Lisp.

At the beginning of the year I wanted to do some toy coding to break out of a Lisp dry spell (the unfortunate result of too much schoolwork - at least I now have that behind me), and, having found out about Radix trees (also known as Patricia trees) recently, I decided to write an implementation for Common Lisp. I just decided to clean it up and put it online - you can find the code here (BSD license). The datastructure itself works for any subtype of sequence. I haven't implemented a version for integers (and unless there is demand, I'm probably not going to), so you'll have to use bit-vectors if you want to index stuff by binary keys.