{-# OPTIONS -fglasgow-exts #-}

class Foo a b where 
   g :: a -> b

type A = {- change the following -} Int
type B = {- change the following -} Char
   
instance Foo A B where
   g a = {- change the following -} ' '
   
type C = {- change the following -} Float
type D = {- change the following -} String

instance Foo C D where
   g c = {- change the following -} ""
  
 
f :: (Foo a b, Foo c d) => a -> c -> (b, d)  
f x y = (g x, g y)