21 Dec
2011
21 Dec
'11
6:02 p.m.
On 21 December 2011 19:29, Ian Lynagh
* There is a new feature constraint kinds (-XConstraintKinds): http://www.haskell.org/ghc/dist/stable/docs/html/users_guide/constraint-kind...
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