Personally I'm more of a fan of immutability than purity, which is why I haven't considered haskell. As mentioned in the post, though, I'm not sure if the language should be static or dynamic or something else.. And I don't really want to invent my own language either. Food for thought :)

Pure functions would let many of your functions become immutable :)

EDIT: Well... not really I guess. But idempotence has similar properties I think.

I don't know much about Clojure, but I understood that it is a lisp and default immutable... so wouldn't that work?