For what it's worth, my usual flow is to start sketching top-down, and building bottom-up afterwards, refactoring as I go. I also (ab)use Clojure's argument destructuring and will often just pass a map until I settle on the "correct" API for my code.

Not bashing good types (I do like Haskell, too), just showing an alternative based on the same brainstorming idea the GP had mentioned.