Incoherent Instance example

{-# LANGUAGE FlexibleInstances, UndecidableInstances #-}

module UpperLowerBounded where

class LowerBounded a where
    lowerBound :: a

class UpperBounded a where
    upperBound :: a

instance {-# INCOHERENT #-} Bounded a => LowerBounded a where
    lowerBound = minBound

instance Bounded a => UpperBounded a where
    upperBound = maxBound

instance {-# INCOHERENT #-} (LowerBounded a, UpperBounded a) => Bounded a where
    minBound = lowerBound
    maxBound = upperBound

data Foo = A | B deriving (Show)
data Bar = C | D | E deriving (Show)

instance Bounded Foo where
    minBound = A
    maxBound = B

instance LowerBounded Bar where
    lowerBound = C

instance UpperBounded Bar where
    upperBound = E