Hi, Am Montag, den 26.03.2018, 14:34 -0400 schrieb Richard Eisenberg:
Bringing this back to the proposal at hand, we would say this to mention a universal:
g (Just *@Int x) = x
and that would mean g :: Maybe Int -> Int
Yes! Something like that and I would fully support the proposal. But
Of course, these little syntactic sigils make Haskell look more Perlish, and that's not a good thing.
is spot-on, and finding a good syntax is the hard part here. And once we have syntax to instantiate universals and bind existentials, there is the question, which of these two deserves @ and which has to get the yet-to-be-found other one. (Personally, I’d say that @ should instantiate universals, for consistency with TypeApplications, but will not insist on this point.) Somewhat tangentially, how much should it worry us that according to the current proposal, in type Id a = a data Foo a where MkFoo :: forall a, a -> Foo a data Foo' a where MkFoo' :: forall a, a -> Foo (Id a) the constructors MkFoo and MkFoo' behave totally different wrt universals and existentials? I see the technical justification for it, but it still feels odd and unsmooth. Cheers, Joachim -- Joachim Breitner mail@joachim-breitner.de http://www.joachim-breitner.de/