69 lines
2.2 KiB
Haskell
69 lines
2.2 KiB
Haskell
{-# LANGUAGE TypeFamilies #-}
|
|
|
|
-- Copyright (C) 2010 John Millikin <jmillikin@gmail.com>
|
|
--
|
|
-- This program is free software: you can redistribute it and/or modify
|
|
-- it under the terms of the GNU General Public License as published by
|
|
-- the Free Software Foundation, either version 3 of the License, or
|
|
-- any later version.
|
|
--
|
|
-- This program is distributed in the hope that it will be useful,
|
|
-- but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
-- GNU General Public License for more details.
|
|
--
|
|
-- You should have received a copy of the GNU General Public License
|
|
-- along with this program. If not, see <http://www.gnu.org/licenses/>.
|
|
|
|
module Network.Protocol.TLS.GNU.ErrorT
|
|
( ErrorT (..)
|
|
, mapErrorT
|
|
) where
|
|
|
|
import Control.Monad (liftM)
|
|
import Control.Monad.Trans (MonadIO, liftIO)
|
|
import Control.Monad.Trans.Class (MonadTrans, lift)
|
|
import qualified Control.Monad.Error as E
|
|
import Control.Monad.Error (ErrorType)
|
|
import qualified Control.Monad.Reader as R
|
|
import Control.Monad.Reader (EnvType)
|
|
|
|
-- A custom version of ErrorT, without the 'Error' class restriction.
|
|
|
|
newtype ErrorT e m a = ErrorT { runErrorT :: m (Either e a) }
|
|
|
|
instance Functor m => Functor (ErrorT e m) where
|
|
fmap f = ErrorT . fmap (fmap f) . runErrorT
|
|
|
|
instance Monad m => Monad (ErrorT e m) where
|
|
return = ErrorT . return . Right
|
|
(>>=) m k = ErrorT $ do
|
|
x <- runErrorT m
|
|
case x of
|
|
Left l -> return $ Left l
|
|
Right r -> runErrorT $ k r
|
|
|
|
instance Monad m => E.MonadError (ErrorT e m) where
|
|
type ErrorType (ErrorT e m) = e
|
|
throwError = ErrorT . return . Left
|
|
catchError m h = ErrorT $ do
|
|
x <- runErrorT m
|
|
case x of
|
|
Left l -> runErrorT $ h l
|
|
Right r -> return $ Right r
|
|
|
|
instance MonadTrans (ErrorT e) where
|
|
lift = ErrorT . liftM Right
|
|
|
|
instance R.MonadReader m => R.MonadReader (ErrorT e m) where
|
|
type EnvType (ErrorT e m) = EnvType m
|
|
ask = lift R.ask
|
|
local = mapErrorT . R.local
|
|
|
|
instance MonadIO m => MonadIO (ErrorT e m) where
|
|
liftIO = lift . liftIO
|
|
|
|
mapErrorT :: (m (Either e a) -> n (Either e' b))
|
|
-> ErrorT e m a
|
|
-> ErrorT e' n b
|
|
mapErrorT f m = ErrorT $ f (runErrorT m)
|