In my experience (using Clojure full time since before there were official releases), Clojure can be written exactly as fast as java. That isn't idiomatic cloju

In my experience (using Clojure full time since before there were official releases), Clojure can be written exactly as fast as java. That isn't idiomatic clojure code however. The features clojure provides are somewhat slower, but well worth it. The purely functional datastructures are ~25% slower than their java equivalents. The seq abstraction is slightly slower, but allows handling infinite sequences, and only passes over the data once. About the only thing I'm aware of that can slow your code down that much is by using reflection in a tight loop. Hop on to #clojure on irc.freenode.net, we'd love to help you out.