Check out nwm:
https://github.com/nizmic/nwm
It's written in XCB and uses Guile. I don't know how complete it is
yet, though. I haven't had much time to play around with it but it seems
to be generally working. It has a REPL and it uses Scheme functions to
manage window placement. I think it would be a better choice. Stumpwm is
huge and I'm pretty sure it has a lot of dependencies on Common Lisp features.
-brandon