data Ex a b = Exc a | Normal b

instance (Show a, Show b)=>Show (Ex a b) where
  show (Normal a) = show a
  show (Exc b) = show b

instance (Eq a, Eq b)=>Eq (Ex a b) where
  Normal x == Normal y = x == y
  Exc x == Exc y = x == y
  _ == _ = False

instance Functor (Ex e) where
  fmap f (Normal a) = Normal (f a)
  fmap f (Exc a) = Exc a

instance Applicative (Ex e) where
  pure = Normal
  (Exc x) <*> _ = Exc x
  _ <*> (Exc x) = Exc x
  (Normal f) <*> (Normal b) = Normal (f b)

instance Monad (Ex e) where
  return = Normal
  (Exc x) >>= func  = Exc x
  (Normal x) >>= func = func x
  _ >> x = x