{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE MultiParamTypeClasses #-}

module Cast where

-- | Type class describing the relationship.
class Cast a b where
  cast :: a -> b

instance Cast Int Bool where
  cast 0 = False
  cast _ = True

instance Cast Bool Int where
  cast False = 0
  cast True  = 1

instance Cast Int Int where
  cast = id

instance Cast Bool Bool where
  cast = id

instance Cast Integer Int where
  cast = fromInteger

instance Cast Integer Bool where
  cast 0 = False
  cast _ = True

instance Cast Int Integer where
  cast = fromIntegral

instance Cast Bool Integer where
  cast False = 0
  cast True  = 1

instance Cast Bool Float where
  cast False = 0.0
  cast True  = 1.0

instance Cast Int Float where
  cast = fromIntegral

-- | "Python-like" addition, with implicit type-based conversion.
pyPlus :: (Cast a Int, Cast b Int) => a -> b -> Int
pyPlus a b = cast a + cast b

-- | "Python-like" conjunction, with implicit type-based conversion.
pyAnd :: (Cast a Bool, Cast b Bool) => a -> b -> Bool
pyAnd a b = cast a && cast b