module  Class.Functor 
export  fmap
where


-- | Class of collection types that can be mapped over.
data Functor (f: Data -> Data) where
        Functor
         :  ([a b: Data]. (a -> b) -> f a -> f b)       -- fmap
         -> Functor f


-- | Apply a function to values of type 'a' in the input collection.
fmap    : [f: Data -> Data]. [a b: Data]
        . Functor f -> (a -> b) -> f a -> f b

fmap (Functor fmap') = fmap'