[bad_user]

I don't know much about Ocaml's modules, however Haskell's type-classes require global uniqueness, which makes them anti-modular. Another problem with Haskell's type-classes is that they are magical, in the sense that they aren't either types or values, hence combining type-classes is always an exercise in frustration. If you want to think of type-classes as being much like OOP interfaces, you're making a mistake. Ironically in Scala, which is the lesser FP language, type-classes are modeled by OOP interfaces and instances are values, so you won't get the same problems.