I think getting to grips with Haskell and the like is worth it even if you are not going to end up using it day to day. In the pst I have been running a program where I was introducing devs to Haskell (immutable data, purism and quickcheck lostly) and then watching how their code evolved in their classical language projects. Over all it always was a great benefit.

Still, I think our industry is seriously behind in the adoption curve of pure force languages. It is mindblowing really that important software is still mainly written in Java C and the likes…