{-# LANGUAGE CPP, NoImplicitPrelude, FlexibleContexts #-} #if __GLASGOW_HASKELL__ >= 702 {-# LANGUAGE Trustworthy #-} #endif ------------------------------------------------------------------------------- -- | -- Module : System.Timeout.Lifted -- Copyright : (c) The University of Glasgow 2007 -- License : BSD-style (see the file libraries/base/LICENSE) -- -- Maintainer : libraries@haskell.org -- Stability : experimental -- Portability : non-portable -- -- Attach a timeout event to monadic computations -- which are instances of 'MonadBaseControl'. -- ------------------------------------------------------------------------------- module System.Timeout.Lifted ( timeout ) where -- from base: import Prelude ( (.) ) import Data.Int ( Int ) import Data.Maybe ( Maybe(Nothing, Just), maybe ) import Control.Monad ( (>>=), return, liftM ) import System.IO ( IO ) import qualified System.Timeout as T ( timeout ) -- from monad-control: import Control.Monad.Trans.Control ( MonadBaseControl, restoreM, liftBaseWith ) #include "inlinable.h" -- | Generalized version of 'T.timeout'. -- -- Note that when the given computation times out any side effects of @m@ are -- discarded. When the computation completes within the given time the -- side-effects are restored on return. timeout :: MonadBaseControl IO m => Int -> m a -> m (Maybe a) timeout t m = liftBaseWith (\runInIO -> T.timeout t (runInIO m)) >>= maybe (return Nothing) (liftM Just . restoreM) {-# INLINABLE timeout #-}