A nice writeup, but I wonder why not just use Scala? It is true that Scala has a steep learning curve compared to Java but you get all of the efficiency with a concise notation. (Substitute Clojure for Scala - just about the same argument, except Clojure is easier to learn.) re: Groovy: too slow - I would rather just use JRuby if I want a slow but really nice programming language on the JVM.