{-# LANGUAGE CPP #-}
{-# LANGUAGE FlexibleInstances #-}
#if __GLASGOW_HASKELL__ >= 706
{-# LANGUAGE PolyKinds #-}
#endif
-----------------------------------------------------------------------------
-- |
-- Copyright : (C) 2011-2015 Edward Kmett
-- License : BSD-style (see the file LICENSE)
--
-- Maintainer : Edward Kmett <ekmett@gmail.com>
-- Stability : provisional
-- Portability : polykinds
--
----------------------------------------------------------------------------
module Data.Groupoid
( Groupoid(..)
) where
import Data.Semigroupoid
import Data.Semigroupoid.Dual
-- | semigroupoid with inverses. This technically should be a category with inverses, except we need to use Ob to define the valid objects for the category
class Semigroupoid k => Groupoid k where
inv :: k a b -> k b a
instance Groupoid k => Groupoid (Dual k) where
inv (Dual k) = Dual (inv k)