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-- |
-- Module : Control.Monad.Trans
-- Copyright : (c) Andy Gill 2001,
-- (c) Oregon Graduate Institute of Science and Technology, 2001
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
-- Portability : portable
--
-- The MonadTrans class.
--
-- Inspired by the paper
-- /Functional Programming with Overloading and
-- Higher-Order Polymorphism/,
-- Mark P Jones (<http://www.cse.ogi.edu/~mpj/>)
-- Advanced School of Functional Programming, 1995.
-----------------------------------------------------------------------------
module Control.Monad.Trans (
MonadTrans(..),
MonadIO(..),
) where
import Prelude
import System.IO
-- ---------------------------------------------------------------------------
-- MonadTrans class
--
-- Monad to facilitate stackable Monads.
-- Provides a way of digging into an outer
-- monad, giving access to (lifting) the inner monad.
class MonadTrans t where
lift :: Monad m => m a -> t m a
class (Monad m) => MonadIO m where
liftIO :: IO a -> m a
instance MonadIO IO where
liftIO = id
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