{-# LANGUAGE CPP #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE Safe #-}
-----------------------------------------------------------------------------
-- |
-- Copyright   :  (C) 2011-2015 Edward Kmett
-- License     :  BSD-style (see the file LICENSE)
--
-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
-- Stability   :  experimental
-- Portability :  non-portable (flexible MPTCs)
--
----------------------------------------------------------------------------
module Data.Semigroupoid.Ob where

import Data.Semigroupoid
import Data.Functor.Bind
import Control.Arrow


#ifdef MIN_VERSION_comonad
import Data.Functor.Extend
import Control.Comonad
#endif

class Semigroupoid k => Ob k a where
  semiid :: k a a

instance (Bind m, Monad m) => Ob (Kleisli m) a where
  semiid :: Kleisli m a a
semiid = forall (m :: * -> *) a b. (a -> m b) -> Kleisli m a b
Kleisli forall (m :: * -> *) a. Monad m => a -> m a
return

#ifdef MIN_VERSION_comonad
instance (Extend w, Comonad w) => Ob (Cokleisli w) a where
  semiid :: Cokleisli w a a
semiid = forall {k} (w :: k -> *) (a :: k) b. (w a -> b) -> Cokleisli w a b
Cokleisli forall (w :: * -> *) a. Comonad w => w a -> a
extract
#endif

instance Ob (->) a where
  semiid :: a -> a
semiid = forall a. a -> a
id