The problem with learning Haskell is I just can't shake the "Research" feeling. Learning Erlang looks a harder slog, but with the benefit of a "Real world" feeling, whether correct or not.
I have separately spent a week learning Erlang and learning Haskell.
Erlang: much much easier to learn. Within a week I felt I could probably have built pretty much whatever I wanted. A few pitfalls, but it's predictable, and with very few difficult to understand parts. Also the OTP is almost CPAN-like in its ability to get you solving problems very quickly. HOWEVER: until the next time I need to build a telephony switch or any kind of massive message handler (chat application, messaging queue, WhatsApp competitor etc), I just have no use for it.
Haskell ... I had some basics in a week. After some months of dabbling here and there, I finally get Monads, but haven't done anything productive yet. I feel like I have become a significantly stronger developer in the other languages I use, have a much deeper understanding of some basics of CompSci, and have had a lot of fun. I think in another few months, it might start being my goto language for solving problems.
Most of the time it's because those people can't make the connection between the research and the "real world". The worlds are very blurred in my experience.
