Quoting Bas van Dijk <v.dijk....@gmail.com>:
I'm playing a bit with the new ConstraintKinds feature in GHC
7.4.1-rc1. I'm trying to give the Functor class an associated
constraint so that we can make Set an instance of Functor. The
following code works but I wonder if the trick with: class Empty a;
instance Empty a, is the recommended way to do this:
Maybe something like this?
class Functor f where
type C f a :: Constraint
type C f a = ()
instance Functor Set where
type C Set a = Ord a
~d
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