Created
October 8, 2016 00:04
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little streaming library
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{-#LANGUAGE BangPatterns #-} | |
import GHC.Magic | |
import Data.IORef | |
import Control.Monad | |
import Control.Monad.Trans | |
data Stream a m r = Yield a (Stream a m r) | Done r | Delay (() -> m (Stream a m r)) | |
instance Functor m => Functor (Stream a m) where | |
fmap f (Done r) = Done (f r) | |
fmap f (Yield a str) = Yield a (fmap f str) | |
fmap f (Delay g) = Delay (\() -> fmap (fmap f) (g ())) | |
instance Monad m => Applicative (Stream a m) where pure = return ; (<*>) = ap | |
instance Monad m => Monad (Stream a m) where | |
return = Done | |
(>>=) = bind_ | |
bind_ str f = case str of | |
Done r -> f r | |
Yield a str -> Yield a (bind_ str f) | |
Delay g -> Delay (\() -> fmap (\s -> bind_ s f)(g ())) | |
instance MonadIO m => MonadIO (Stream a m) where | |
liftIO = liftio | |
{-#INLINE liftIO #-} | |
liftio :: MonadIO m => IO r -> Stream a m r | |
liftio m = Delay (oneShot (\() -> fmap Done (liftIO m))) | |
{-#INLINE [1] liftio #-} | |
{-#RULES | |
"liftio hack" forall m f . liftio m >>= f = Delay (oneShot (\() -> fmap f (liftIO m))) | |
#-} | |
yield :: Monad m => a -> Stream a m () | |
yield a = Yield a (Done ()) | |
next :: Monad m => Stream t m a -> m (Either a (t, Stream t m a)) | |
next str = case str of | |
Done r -> return (Left r) | |
Yield a rest -> return (Right (a,rest)) | |
Delay f -> f () >>= next | |
stream :: Int -> Int -> IORef Int -> Stream Int IO () | |
stream !m limit ref = when (m < limit) $ do | |
n <- liftIO (readIORef ref) | |
yield n | |
stream (m+1) limit ref | |
counter :: IORef Int -> Stream Int IO r -> IO Int | |
counter ref = loop 0 where | |
loop n str = do | |
e <- next str | |
case e of | |
Left _ -> return n | |
Right (a,rest) -> do | |
writeIORef ref $! n+1 | |
loop (n+1) rest | |
main = do | |
ref <- newIORef 0 | |
let send = stream 0 large ref | |
large = 10000000 :: Int | |
counter ref send | |
readIORef ref >>= print | |
counter ref send | |
readIORef ref >>= print |
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