Re: [Haskell-cafe] How to bring existentially quantified type variables into scope

On Aug 10, 2017, at 5:08 PM, Wolfgang Jeltsch wrote:

Is there also a solution that does not involve using this (unimplemented) feature?

I get the feeling there is a better way to do this, but I found something of a hack that I think does what you want. Using Data.Type.Equality, you can match on Refl to bring the `b` into scope. import Data.Type.Equality f :: forall a. IsListType a -> () f IsListType = case Refl of (Refl :: (a :~: [b])) -> () This is sort of silly, though. Alexis