You can do that in Haskell as well though [0]. With ghci, making a code change is almost instantaneous even for big code bases, and you are assured that your code is self consistent. Then mess with your long-running state all you want.

At least for backend stuff, this is no worse than Clojure.

Give it a try :) Ping me if you have any questions.

[0] http://chrisdone.com/posts/ghci-reload