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{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{- |
This module is an alternative version of "Control.Monad.Par" in
which the `Par` type provides `IO` operations, by means of `liftIO`.
The price paid is that only `runParIO` is available, not the pure `runPar`.
This module uses the same default scheduler as "Control.Monad.Par".
-}
module Control.Monad.Par.IO
( ParIO, IVar, runParIO
-- And instances!
)
where
import Control.Monad.Par.Scheds.Trace (Par, IVar)
import qualified Control.Monad.Par.Scheds.TraceInternal as Internal
import Control.Monad.Par.Class
import Control.Applicative
import Control.Monad.Trans (liftIO, MonadIO)
import Control.Monad.Fix (MonadFix)
-- | A wrapper around an underlying Par type which allows IO.
newtype ParIO a = ParIO (Par a)
deriving (Functor, Applicative, Monad, ParFuture IVar, ParIVar IVar, MonadFix)
-- | A run method which allows actual IO to occur on top of the Par
-- monad. Of course this means that all the normal problems of
-- parallel IO computations are present, including nondeterminism.
--
-- A simple example program:
--
-- > runParIO (liftIO $ putStrLn "hi" :: ParIO ())
runParIO :: ParIO a -> IO a
runParIO (ParIO p) = Internal.runParIO p
instance MonadIO ParIO where
liftIO io = ParIO (Internal.Par (Internal.LiftIO io))
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