Generative functors indeed fixes the issue, but it’s kind of interesting because they’re similar in a way to newtypes. In each case, you generate a new type, distinct from the others, which holds a new implementation of the same interfaces.

It comes down to ergonomics where OCaml’s approach tends to make local reasoning easier and Haskell’s approach makes it a little easier to transform structurally isomorphic types into one another by wrapping/unwrapping.