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|
{-# LANGUAGE CPP #-}
#if __GLASGOW_HASKELL__ >= 702
{-# LANGUAGE Safe #-}
#endif
#if __GLASGOW_HASKELL__ >= 708
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE StandaloneDeriving #-}
#endif
-----------------------------------------------------------------------------
-- |
-- Module : Control.Monad.IO.Class
-- Copyright : (c) Andy Gill 2001,
-- (c) Oregon Graduate Institute of Science and Technology, 2001
-- License : BSD-style (see the file LICENSE)
--
-- Maintainer : R.Paterson@city.ac.uk
-- Stability : experimental
-- Portability : portable
--
-- Class of monads based on @IO@.
-----------------------------------------------------------------------------
module Control.Monad.IO.Class (
MonadIO(..)
) where
#if __GLASGOW_HASKELL__ >= 708
import Data.Typeable
#endif
-- | Monads in which 'IO' computations may be embedded.
-- Any monad built by applying a sequence of monad transformers to the
-- 'IO' monad will be an instance of this class.
--
-- Instances should satisfy the following laws, which state that 'liftIO'
-- is a transformer of monads:
--
-- * @'liftIO' . 'return' = 'return'@
--
-- * @'liftIO' (m >>= f) = 'liftIO' m >>= ('liftIO' . f)@
class (Monad m) => MonadIO m where
-- | Lift a computation from the 'IO' monad.
liftIO :: IO a -> m a
#if __GLASGOW_HASKELL__ >= 708
deriving instance Typeable MonadIO
#endif
instance MonadIO IO where
liftIO = id
|
