3 ms·

lps25: > Consider the case of a set implemented as a binary tree. The type of such a set should be parametrised by the type of the elements and the ordering us

lps25: > Consider the case of a set implemented as a binary tree. The type of such a set should be parametrised by the type of the elements and the ordering used. With applicative functors this is the case as your set type will be `Set(O).t` where `O` is a structure containing the type and the ordering. With generative functors each individual set type is abstract -- so the type itself is not parameterised by the ordering. You make a good point about this not being strictly about type classes. But I'd say that the issue is only a problem in the presence of implicit resolution, since otherwise, you can just bind the result of the functor to a structure once and be done with it. It becomes an issue with type classes, because you don't have the choice to share a single structure during elaboration. IMO, the generative version is still better for most use-cases (pure or not), but it's nice that you can have both in OCaml.

jordwalke 12y ago
>> since otherwise, you can just bind the result of the functor to a structure once.. My understanding was that of lpw25's. I wanted to use applicative functors in the same way type classes (or OCaml's modular implicits) would make use of them, but even without type class's implicit resolution (explicitly specifying them). I agree there isn't too much difference from doing the same with generative functors, but the main difference is, as you said, I would need to find a place (some appropriately accessible location in the namespace) by which to access the result of these generative functor applications, and that's just an extra point of friction (if I understand correctly). It's not the end of the world as you said either way because we can do either. Thanks for the help, jonsterling/lpw25.