ConstraintKinds and default associated empty constraints

[Bas van Dijk]

On 22 December 2011 09:31, Simon Peyton-Jones <simonpj at microsoft.com> wrote:
> What about
>
> class Functor f where
>    type C f :: * -> Constraint
>    type C f = ()
>
> After all, just as (Ord a, Show a) is a contraint, so is ().

But there's a kind mis-match there. `C f` should have kind `* ->
Constraint` but () has kind *. Or do I have to enable some language
extension to make this work?

Thanks,

Bas