ANNOUNCE: GHC 7.4.1 Release Candidate 1

[Bas van Dijk]

On 21 December 2011 19:29, Ian Lynagh <igloo at 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