On Sat, Jul 31, 2021 at 7:14 PM Henning Thielemann
[...] A more modern approach would use type functions:
class Setish set where type Element set empty :: set singleton :: Element set -> set
Thanks for the pointer.
My question is how does the functional dependency in Setish interact with "extra" types needed for richer set operations like finding the powerset or taking a cartesian product?
powerset would need a type like:
powerset :: (Powersettish powerset, Element powerset ~ set, Setish set) => set -> powerset
with an extra Powersettish class.
However, the type checker could not guess the exact powerset type, it could be, e.g. powerset :: Set a -> Set (Set a) or powerset :: Set a -> [Set a]
Okay, I'm starting to see why the "Set" typeclass examples I could find don't include a powerset or cartesian product method. Thanks again, Stu