I mean in terms of the philosophy behind it. A programming language is a tool for thinking. And each language, fits better with some specific way of thinking about a problem. So you are mastering a programming language when you can adapt the way you think about the problem to fit the best characteristics of that language. And i feel the discussion about using Scala or Clojure should be more about that, and not so much about the amount of code needed to write a program on each one, or the fact that one has Type Inference in its nature, while in the other it is optional. Just my 2 cents ;)