Multi-Parameter Classes

Define relations between classes.

class Collection c a where

empty :: c

add :: a -> c -> c

member :: a -> c -> Bool

c is a collection with elements of type a.

instance Eq a =>

Collection [a] a where

empty = []

add = (:)

member = elem

instance Ord a =>

Collection (Tree a) a where

empty = Leaf

add = insertTree

member = elemTree