So I worked exclusively in the statically typed (and imperative / OO) world for the first 10 years of my professional career. Several years ago I decided to learn functional programming. I started with Scheme and moved to Clojure. I really enjoy Clojure; it's a real joy coding in it using Emacs with paredit (or smartparens).

I wrote a REST API using Clojure; the code also has to interact with a Postgres database. This is for a side project, but it's not a trivial code base. I definitely miss Java/Eclipse style refactoring (right-click, rename, and EVERYTHING is properly updated). Can't do that in Clojure. Also, I find that I have to write more unit tests with Clojure in order to make up for the fact the compiler can't help me. Not that I wouldn't write tests in Java; but I find I have to write more in Clojure to keep the codebase manageable.

So again, for me, I use unit testing to make up for the fact I don't have the compiler helping me as much.