BindAsync.hs

-- Bind an async to be cancelled when the current computation ends.
bindAsync :: IO a -> ContT r IO ()
bindAsync m = do
    ContT $ \cc -> do
        withAsync m . const $ cc ()

-- Use bindAsync to auto-cancel the thread when the containing computation finishes
testBoundAsync :: ContT r IO ()
testBoundAsync = do
    bindAsync . forever $ print "can you hear me now?"
    liftIO $ threadDelay 1000000

-- The "traditional" way to accomplish the same thing
-- Notice the need for nesting.
-- It does however give you explicit control over when the async is cancelled, and gives
-- you access to the result of the async if you need it.
testWithAsync :: IO ()
testWithAsync = do
    withAsync (forever $ print "can you hear me now?") $ \handle -> do
        liftIO $ threadDelay 1000000

-- This version does NOT bind the thread to its containing context
-- and thus will annoyingly print forever.
testSimpleAsync :: ContT r IO ()
testSimpleAsync = do
    liftIO . async . forever $ print "can you hear me now?"
    liftIO $ threadDelay 1000000