[mikorym]

I once googled "functional programming for category theorists" and obviously got instead to "category theory for programmers" (incidentally I use Milewski's book in this reverse way).

I still have a rudimentary understanding of functional programming (apart from the canonical "it's just an implementation of lambda calculus"). And I have to say that without exercise and training one grabs at wisps and mist. In mathematics it's also like this, you often have your favorite prototypical monad, adjunction, group, set, etc. (e.g.: The adjunction Set->Set^op by powerset is a strong contender.) And I view axiomatic systems in essence as sort of list of computational rules (e.g.: transitive closure).

I haven't found some idiosyncratic project to code in Haskell yet though...