ANNOUNCE: GHC 7.4.1 Release Candidate 1

[Bas van Dijk]

On 22 December 2011 00:10, José Pedro Magalhães <jpm at cs.uu.nl> wrote:
> Hi Bas,
>
> On Wed, Dec 21, 2011 at 23:02, Bas van Dijk <v.dijk.bas at gmail.com> wrote:
>>
>> 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?
>
>
> 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
>>
>>
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>> Glasgow-haskell-users at haskell.org
>> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
>
>

Thanks Pedro, that works. I already read through the docs of GHC.Prim
but could not find it:

http://www.haskell.org/ghc/dist/stable/docs/html/libraries/ghc-prim-0.2.0.0/GHC-Prim.html

I guess haddock is not smart enough to understand kinds yet...