BowenFu
Implement try
Implement throw_<A>, throwIO<A>, and
onException io what
= io catch \e -> do _ <- what
throwIO (e :: SomeException)
data Async a = Async (MVar (Either SomeException a)) -- async :: IO a -> IO (Async a) async action = do var <- newEmptyMVar forkIO (do r <- try action; putMVar var r) -- return (Async var) waitCatch :: Async a -> IO (Either SomeException a) -- waitCatch (Async var) = readMVar var wait :: Async a -> IO a -- wait a = do r <- waitCatch a case r of Left e -> throwIO e Right a -> return a
bracket :: IO a -> (a -> IO b) -> (a -> IO c) -> IO c bracket before after during = do
a <- before
c <- during a onException after a after a
return c
finally :: IO a -> IO b -> IO a finally io after = do
io onException after after
waitEither :: Async a -> Async b -> IO (Either a b) waitEither a b = do m <- newEmptyMVar forkIO $ do r <- try (fmap Left (wait a)); putMVar m r forkIO $ do r <- try (fmap Right (wait b)); putMVar m r wait (Async m)
waitAny :: [Async a] -> IO a waitAny as = do m <- newEmptyMVar let forkwait a = forkIO $ do r <- try (wait a); putMVar m r mapM_ forkwait as wait (Async m)