ContT is more pragmatic than Cont，with this powerful abstraction, I could
effectively abstract away callbacks and listener in Android. My next
exploration is to port coroutineT to Frege
module examples.MyCont where
class MonadIO m where
--- Lift a computation from the 'IO' monad.
liftIO :: IO a -> m a
class MonadTrans t where
--- Lift a computation from the argument monad to the constructed monad.
lift :: Monad m => m a -> t m a
instance MonadIO IO where
liftIO io = io
instance MonadTrans (ContT r) where
lift m = ContT (m >>=)
instance (Monad m, MonadIO m) => MonadIO (ContT r m) where
liftIO = lift . liftIO
data ContT r m a = ContT { runContT :: (a -> m r) -> m r }
instance Monad (ContT r m) where
pure x = contT ($ x)
m >>= k = contT $ \c -> runContT m (\x -> runContT (k x) c)
contT :: ((a -> m r) -> m r) -> ContT r m a
contT f = ContT { runContT = f }
runContT :: ContT r m a -> ((a -> m r) -> m r)
runContT c = ContT.runContT c
callCC :: ((a -> ContT r m b) -> ContT r m a) -> ContT r m a
callCC f = ContT $ \c -> ContT.runContT (f (\a -> ContT $ \_ -> c a)) c
data Data = native java.util.Date where
native new :: () -> IO (MutableIO Data)
native toString :: Mutable s Data -> ST s String
current :: IO String
current = do
d <- Data.new ()
d.toString
fun :: Int -> IO String
fun = (`runContT` id) $ do
callCC $ \exit1 -> do
exit1 $ liftIO current
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