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