Re: Functor instance for Set?

On 01/03/12 09:31, Bas van Dijk wrote:

class Functor f where type FunctorConstraint f :: * -> Constraint type FunctorConstraint f = Empty

fmap :: (FunctorConstraint f b) => (a -> b) -> f a -> f b

class Empty a instance Empty a

Do you really need this Empty class? That seems inconvenient. I had hoped you would be able to write something like type FunctorConstraint f :: * -> Constraint type FunctorConstraint f a = () Twan