Color.hs

{-# LANGUAGE FlexibleInstances, UndecidableInstances #-}
class Color a where
  toValue :: a -> (Int, Int, Int)

data Red = Red deriving Show
data Blue = Blue deriving Show

instance Color Red where
  toValue _ = (255, 0, 0)

instance Color Blue where
  toValue _ = (0, 255, 0)


class YesNo a where
  yesno :: a -> Bool

instance YesNo Char where
  yesno _ = True

instance YesNo [a] where
  yesno [] = False
  yesno _ = True

instance (Integral a) => YesNo a where
  yesno n 
    | toInteger n == 0 = False
    | otherwise = True