Here's another option for building a lisp-descendant from Scheme.

http://t3x.org/s9book/index.html

"Scheme9 from Empty Space"

I've not tried any of these. I'd be interested in someone who's done the lot (Lisp in Small Pieces, the Haskell one, and these two C-created lisps) giving a take on each. Making a lisp or forth seems like a great way to learn [x] thing.