Also I found Dialyzer (success typing checker) to be helpful in large projects:

http://learnyousomeerlang.com/dialyzer

The way success typing works it is a bit like static typing but when it cannot deduce the types it assumes success. However when it finds a discrepancy it is always right. So the more type annotations you add, and the more precise they are the more benefits you get from it.

It has also been there for many years. I think Python only very recently has started getting the same kind of things via MyPy. Of course, they had to call it something differently (Optional Static Typing).

Elixir has a wrapper around it, it seems: https://github.com/jeremyjh/dialyxir but never used it (I user Erlang mostly).