Hi Bas, On Wed, Dec 21, 2011 at 23:02, Bas van Dijk <v.dijk....@gmail.com> wrote:
> 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? > Yes: GHC.Prim. (Which reminds me, Simon, we had agreed to re-export Constraint from GHC.Exts, but it wasn't clear to me how to do this, since Constraint is a kind, not a type, so it can't just go on the export list of the module...) Cheers, Pedro > > Cheers, > > Bas > > _______________________________________________ > Glasgow-haskell-users mailing list > Glasgow-haskell-users@haskell.org > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users >
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