I love the developer-friendliness of Elixir syntax and the robustness + power of the Erlang VM. However, I really miss the type system and cool mathy things of Haskell (eta reduction for example).

Is there a language on the BEAM that has strong functional features of Haskell?

There's Purerl[1] which is purescript erlang backend.

[1]https://github.com/purerl/purerl