Learn Haskell, it significantly changed the way I think about programming and those new perspectives have been applicable in the other languages I've written in

Learn Haskell, it significantly changed the way I think about programming and those new perspectives have been applicable in the other languages I've written in. Lisp is good, but I think Haskell will broaden your horizons more. The only problem is Haskell is really hard to learn and there aren't a ton of good learning resources. I suggest learning a simpler, similar language Elm, to start thinking functionally, and then move on to Haskell.