Erlang has dialyzer type checker. Depending on how well users refine their types that can produce very good results. Combine that with property checker (PropEr or QuickCheck) + Erlang's default process isolation and fault tolerance, and I think it can make for a more reliable system. I think I'll take that into production over just having a statically typed program. (Just going off my gut feeling and experience).

http://learnyousomeerlang.com/dialyzer

( not sure if Elixir supports it though, but it seems so:

http://elixir-lang.org/docs/stable/Kernel.Typespec.html )