module Data.Group
( module Data.Monoid.Additive
, Group
, gnegate
, minus
) where
import Data.Monoid.Additive
import Data.Monoid.Monad.Identity
import Data.Monoid.FromString
infixl 6 `minus`
class Monoid a => Group a where
gnegate :: a -> a
minus :: a -> a -> a
a `minus` b = a `plus` gnegate b
instance Num a => Group (Sum a) where
gnegate = Sum . negate . getSum
Sum a `minus` Sum b = Sum (a b)
instance Fractional a => Group (Product a) where
gnegate = Product . negate . getProduct
Product a `minus` Product b = Product (a / b)
instance Group a => Group (Dual a) where
gnegate = Dual . gnegate . getDual
instance Group a => Group (Identity a) where
gnegate = Identity . gnegate . runIdentity
Identity a `minus` Identity b = Identity (a `minus` b)
instance Group a => Group (FromString a) where
gnegate = FromString . gnegate . getFromString
FromString a `minus` FromString b = FromString (a `minus` b)