For what it's worth, I've been using Haskell in production at Bitnomial, a financial exchange, and LLMs + Haskell is an extremely productive combo.

Since Opus 4.6, LLMs have been pretty clever at using fancy types with libraries like Servant and Beam. The expressiveness of the types, combined with feedback from the compiler, means that agents converge quickly to something that works. I don't think I've noticed agents having to run the compiler so often that compilation speed is an issue.

I'd be very curious to hear your take if you gave another language a proper try for comparison with the same tools. I think you'll be as surprised as we were.