Re: [Haskell-cafe] Re: [Haskell] View patterns in GHC: Request for feedback

On Jul26, apfelmus wrote:

Yes, the types of the patterns don't unify. But each one is a specialization of the argument type. Note that the type signature is

bar :: (forall a . ViewInt a => a) -> String

which is very different from

bar :: forall a . ViewInt a => a -> String

Without the extension, we would write bar as follows

bar :: (forall a . ViewInt a => a) -> String bar x = let xNat = x :: Nat in case xNat of Zero -> ... _ -> let xListBool = x :: [Bool] in case xListBool of True:xs -> ...

In other words, we can specialize the polymorphic argument to each pattern type and each equation may match successfully.

Oh, I understand what you're saying now. Thanks for clarifying! -Dan