I definitely plan to learn some Prolog, but I don't know when. For now I plan on learning Datalog because it is used (or a variation on it is used) in Datomic.

The relation between Prolog, Datalog and the "Datalog-like" query language used by Datomic is still not clear at all to me but hopefully soon the picture shall get clearer.

I know it's OT but that's what I really like about Clojure: Clojure taught me about Lisp (even if it's not a 100% pure Lisp), functional programming (even if it's not 100% purely functional), lazyness, monads (yup, really) and now it's probably going to introduce me, thanks to Datomic, to Datalog...