You always have dynamic typing as an escape. If that's what it takes, then that's an option, but I think in practice you'd be able to keep that sort of purity to a small portion of the program.

Haskell is a research language, which sometimes shows in the libraries. I'm not sure if I'd recommend it for general use; I'm more partial to Kotlin these days. It's definitely an interesting approach, though, and anyone who's designing languages ought to make themselves familiar.