Adding class constraints to typeclass instance
- by BleuM937
I'm trying to implement the Cantor Pairing Function, as an instance of a
generic Pair typeclass, as so:
module Pair (Pair, CantorPair) where
-- Pair interface
class Pair p where
pi :: a -> a -> p a
k :: p a -> a
l :: p a -> a
-- Wrapper for typing
newtype CantorPair a = P { unP :: a }
-- Assume two functions with signatures:
cantorPair :: Integral a => a -> a -> CantorPair a
cantorUnpair :: Integral a => CantorPair a -> (a, a)
-- I need to somehow add an Integral a constraint to this instance,
-- but I can't work out how to do it.
instance Pair CantorPair where
pi = cantorPair
k = fst . cantorUnpair
l = snd . cantorUnpair
How can I add the appropriate Integral constraint to the instance?
I have a vague feeling I might need to modify the Pair interface itself,
but not sure how to go about this.
