> functional programming (from the mathematical side it corresponds to various lambda calculi) And category theory, in the case of Haskell. (and yes, to work

> functional programming (from the mathematical side it corresponds to various lambda calculi) And category theory, in the case of Haskell. (and yes, to work with Haskell at a basic level, category theory isn't required. But as someone who is learning the basics of category theory, it sure helps understand the "why" behind a lot of things if you move to a more advanced level.)