On 21 December 2011 19:29, Ian Lynagh <ig...@earth.li> wrote:
> * There is a new feature constraint kinds (-XConstraintKinds):
>
> http://www.haskell.org/ghc/dist/stable/docs/html/users_guide/constraint-kind.html
I'm trying to run the ConstraintKinds example from the documentation:
{-# LANGUAGE ConstraintKinds, TypeFamilies #-}
type family Typ a b :: Constraint
type instance Typ Int b = Show b
type instance Typ Bool b = Num b
But GHC complains:
Not in scope: type constructor or class `Constraint'
Do I have to import some GHC module for this?
Cheers,
Bas
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