[conaws]

The fact that folks in the comments are complaining here about Clojure's error messages here tells me that the implications of this post might not be obvious. Up to this point, it has been really really hard to give good error messages from macros, and a lot of the core functionality of Clojure (let, defn etc etc) are from macros. What Clojure.spec means (if I'm correct) is that in the future, not only will the Clojure language itself be able to have sane error messages, you'll be able to easily create sane error messages for yourself from your own code. This is a HUGE HUGE deal. It is quite possibly BETTER than any type system. http://clojure.org/about/spec Also, the idea that you'll be able to get generative testing FOR FREE, is just totally insane.