Re: [Haskell-cafe] arbitrary rank polymorphism and ghc language pragmas

On 05/07/12 17:18, rickmurphy wrote:

Hi All:

I've been working through some details in these papers [1], [2] and noticed a language pragma configuration that I hope you can confirm.

When using explicit foralls in a data constructor, it appears that GHC 7.4.2 requires Rank2Types in the Language pragma for what the papers consider rank 1 types.

Here's an example:

data T = TC (forall a b. a -> b -> a)

Am I correct, or is there another extension? The ExplicitForAll does not appear to support rank 1 types in data constructors.

There is the PolymorphicComponents extension precisely for this use case. Twan