----------------------------------------------------------------------------- -- | -- 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 : ross@soi.city.ac.uk -- Stability : experimental -- Portability : portable -- -- Class of monads based on @IO@. ----------------------------------------------------------------------------- module Control.Monad.IO.Class ( MonadIO(..) ) where import System.IO (IO) -- | 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 instance MonadIO IO where liftIO = id