ANNOUNCE: GHC 7.4.1 Release Candidate 1

Bas van Dijk v.dijk.bas at
Thu Dec 22 00:02:04 CET 2011

On 21 December 2011 19:29, Ian Lynagh <igloo at> wrote:
>  * There is a new feature constraint kinds (-XConstraintKinds):

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?



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