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|
{-# LANGUAGE MultiParamTypeClasses
, FunctionalDependencies
, FlexibleInstances
, UndecidableInstances #-}
-----------------------------------------------------------------------------
-- |
-- Module : Control.Comonad.Cofree.Class
-- Copyright : (C) 2008-2011 Edward Kmett
-- License : BSD-style (see the file LICENSE)
--
-- Maintainer : Edward Kmett <ekmett@gmail.com>
-- Stability : experimental
-- Portability : fundeps, MPTCs
----------------------------------------------------------------------------
module Control.Comonad.Cofree.Class
( ComonadCofree(..)
) where
import Control.Applicative
import Control.Comonad
import Control.Comonad.Trans.Env
import Control.Comonad.Trans.Store
import Control.Comonad.Trans.Traced
import Control.Comonad.Trans.Identity
import Data.Semigroup
class (Functor f, Comonad w) => ComonadCofree f w | w -> f where
unwrap :: w a -> f (w a)
instance ComonadCofree f w => ComonadCofree f (IdentityT w) where
unwrap = fmap IdentityT . unwrap . runIdentityT
instance ComonadCofree f w => ComonadCofree f (EnvT e w) where
unwrap (EnvT e wa) = EnvT e <$> unwrap wa
instance ComonadCofree f w => ComonadCofree f (StoreT s w) where
unwrap (StoreT wsa s) = flip StoreT s <$> unwrap wsa
instance (ComonadCofree f w, Semigroup m, Monoid m) => ComonadCofree f (TracedT m w) where
unwrap (TracedT wma) = TracedT <$> unwrap wma
|
