I'm trying to update container-classes to duplicate the pre-existing classes defined in the Prelude (Functor, etc.) and am trying to get my approach on how to have functions/classes that work on types of kind * (e.g. Bytestring) as well as kind * -> * (e.g. lists), as my previous approach didn't work. To define the connection, I've copied the style set out by Ganesh's rmonad ( http://hackage.haskell.org/package/rmonad ) package: ,---- | -- | Indicates what kind of value may be stored within a type. Once | -- superclass constraints are available, the @v@ parameter will | -- become an associated type. | class Stores c v | c -> v | | data family Constraints :: (* -> *) -> * -> * | | class (Stores (c v) v) => Suitable c v where | constraints :: Constraints c v `---- This works. However, what doesn't work is when I try to use these classes to re-define Functor: ,---- | class (Stores c v) => Mappable c v where | rigidMap :: (v -> v) -> c -> c | | class (Mappable (c v) v) => Functor c where | fmap :: (Suitable c a, Suitable c b) => (a -> b) -> c a -> c b `---- GHC doesn't like this definition of Functor; the only way to get it to work is to make `v' a parameter of the Functor class as well, even though it doesn't actually get used. Why is this? Is there any way around it? (Limitations like this are making me more and more consider dumping this whole concept as it's just becoming a pain, but more importantly rather boring :s) -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com