On Sat, Jan 29, 2022 at 07:59:51PM -0500, David Feuer wrote:
One is that `containers` has a long history of attempting to remain compatible with potential future Haskell 98-like Haskell implementations (likely with a few days of work to patch up mistakes when the time comes). Using a GADT to define Set would break that quite thoroughly.
Yes, that's definitely an issue.
My second concern is more practical:
type Set a = SetImpl a a
is all sorts of problematic. It forces anyone who wants to use what's always been the `Set` type constructor (Set :: Type -> Type) to dig into the implementation and use `SetImpl :: Type -> Type -> Type` instead. That's quite a different beast.
Well, they could use the unsaturated type alias in some cases, but there are likely situations where that's not an option.
I don't know all the things that will break, but they'll surely include https://hackage.haskell.org/package/constrained-monads-0.5.0.0/docs/Control-....
Yes, that would break irreperably
I think the real answer is to remove `elem` from `Foldable` and put it somewhere more appropriate.
Perhaps so, though my guess is that this is unlikely to happen... Overall, your objections are likely sufficient. -- Viktor.