I'm not a Clojure expert, so I can't directly address that, but from the little that I know of Clojure though, I think you can do that by binding a function to a var, and then changing the binding of the var. (Can any Clojure experts exlaborate?)

Regardless, every Lisp that I am able to comment on (newLISP, elisp, Scheme, CL) can do that easily, so I doubt that Clojure would have difficulty with this.

It does have difficulty with this, check the mailing list. Just because something using s-expressions doesn't mean you can override functions in a namespace.

http://groups.google.com/group/clojure/browse_thread/thread/...;

Thanks for that interesting thread! I do know though that newLISP can do this easily with a simple 'set' call.