haskell inheritance

Subtype.hs

{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, FlexibleContexts #-}
module Subtype where

data Derived super sub = Derived super sub

class IsInstance b a where
  getData :: (a -> v) -> b -> v
  setData :: (a -> s -> s) -> b -> s -> s

instance IsInstance (Derived a b) a where
  getData getter (Derived a _) = getter a
  setData setter (Derived a _) = setter a

instance IsInstance b c => IsInstance (Derived a b) c where
  getData getter (Derived _ b) = getData getter b
  setData setter (Derived _ b) = getData setter b

data Super = Super {name :: String}
data Sub = Sub {age :: Int}

getName :: IsInstance b Super => b -> String
getName = getData name

getAge :: IsInstance b Sub => b -> Int
getAge = getData age