Definitely Prolog. I have barely played with Prolog except when it is included in the PL as in picoLisp or Shen, but it's in its own category. I agree about Erlang too, but it made me stop to think. Erlang without the BEAM or OTP is pretty much a functional language like Haskell, no? I looked at Pony once. Yeah, ok, Erlang too! I prefer the Lisp version: LFE!