I worked in a Haskell environment that used a lot of formal methods & some of those tools, such as Agda, would generate Haskell that could then be optimized for performance. It was pretty wild but for me, a test engineer, was a pain for more boring tasks like JSON parsing or calling Rest APIs etc :) It got me into property based testing though, and now I'm much more type-driven, so there were some really cool perks of working in such an env.