-- |
-- Module      : OAlg.Data.Opposite
-- Description : predicate for the opposite
-- Copyright   : (c) Erich Gut
-- License     : BSD3
-- Maintainer  : zerich.gut@gmail.com
--
-- predicate for the opposite.
module OAlg.Data.Opposite
  (
    -- * Op
    Op(..), fromOp, fromOpOp

    -- * Op2
  , Op2(..)
      
  ) where

import OAlg.Data.Show
import OAlg.Data.Equal
--------------------------------------------------------------------------------
-- Op -

-- | Predicate for the opposite of a type @__x__@. 
newtype Op x = Op x deriving (Show,Read,Eq)

-- | from @'Op' x@.
fromOp :: Op x -> x
fromOp (Op x) = x

-- | from @'Op' ('Op' x)@.
fromOpOp :: Op (Op x) -> x
fromOpOp (Op (Op x)) = x


--------------------------------------------------------------------------------
-- Op2 -

-- | Predicat for the opposite of a two parametrized type @__h__@ where
--   the two parameters @__x__@ and @__y__@ are switched
newtype Op2 h x y = Op2 (h y x)

instance Show2 h => Show2 (Op2 h) where
  show2 (Op2 h) = "Op2[" ++ show2 h ++ "]"

instance Eq2 h => Eq2 (Op2 h) where
  eq2 (Op2 f) (Op2 g) = eq2 f g