As another data point, I had been doing Ruby for five years when I switched to Clojure. After a single year in Clojure, I knew the language much better than I h

As another data point, I had been doing Ruby for five years when I switched to Clojure. After a single year in Clojure, I knew the language much better than I had ever known Ruby and was able to read the source for the compiler itself and spot issues in it. Common Lisp is a lot more complicated than Clojure, but certainly simpler than Ruby. Personally I had a hard time remembering the difference between Procs, blocks, and lambdas in Ruby, though I believe this is partly due to the fact that the differences shifted in minor point releases.