module Data.Pipe (
PipeClass(..), Pipe, runPipe, finalize, finally, bracket ) where
import Control.Applicative
import Control.Monad
import Control.Exception.Lifted (onException)
import Control.Monad.Trans.Control
import "monads-tf" Control.Monad.Trans
class PipeClass p where
(=$=) :: Monad m => p a b m x -> p b c m y -> p a c m y
yield :: Monad m => o -> p i o m ()
await :: Monad m => p i o m (Maybe i)
data Pipe i o m r
= Ready (m ()) o (Pipe i o m r)
| Need (m ()) (Maybe i -> Pipe i o m r)
| Done (m ()) r
| Make (m ()) (m (Pipe i o m r))
finalizer :: Pipe i o m r -> m ()
finalizer (Ready f _ _) = f
finalizer (Need f _) = f
finalizer (Done f _) = f
finalizer (Make f _) = f
instance PipeClass Pipe where
p =$= Done f r = Done (finalizer p >> f) r
p =$= Ready f o p' = Ready f o $ p =$= p'
Need f n =$= p = Need f $ \i -> n i =$= p
Ready _ o p =$= Need _ n = p =$= n (Just o)
Done f r =$= Need f' n =
Done (return ()) r =$= Make f' (f >> return (n Nothing))
Make f m =$= p = Make f $ (=$= p) `liftM` m
p =$= Make f m = Make f $ (p =$=) `liftM` m
yield x = Ready (return ()) x (return ())
await = Need (return ()) return
instance Monad m => Monad (Pipe i o m) where
Ready f o p >>= k = Ready f o $ p >>= k
Need f n >>= k = Need f $ \i -> n i >>= k
Done _ r >>= k = k r
Make f m >>= k = Make f $ (>>= k) `liftM` m
return = Done (return ())
instance Monad m => Functor (Pipe i o m) where
fmap = (=<<) . (return .)
instance Monad m => Applicative (Pipe i o m) where
pure = return
(<*>) = liftM2 id
instance MonadTrans (Pipe i o) where
lift = liftP
runPipe :: Monad m => Pipe i o m r -> m (Maybe r)
runPipe (Done f r) = f >> return (Just r)
runPipe (Make _ m) = runPipe =<< m
runPipe _ = return Nothing
liftP :: Monad m => m a -> Pipe i o m a
liftP m = Make (return ()) $ Done (return ()) `liftM` m
bracket :: MonadBaseControl IO m =>
m a -> (a -> m b) -> (a -> Pipe i o m r) -> Pipe i o m r
bracket o c p = do
h <- liftP o
p h `finally` (c h >> return ())
finalize :: Monad m => Pipe i o m r -> m b -> Pipe i o m r
finalize (Ready _ o p) f = Ready (f >> return ()) o $ finalize p f
finalize (Need _ n) f = Need (f >> return ()) $ \i -> finalize (n i) f
finalize (Done _ r) f = Done (f >> return ()) r
finalize (Make _ m) f = Make (f >> return ()) $ flip finalize f `liftM` m
finally :: MonadBaseControl IO m => Pipe i o m r -> m b -> Pipe i o m r
finally p f = finalize (mapMake (`onException` f) p) f
mapMake :: Monad m => (forall a . m a -> m a) -> Pipe i o m r -> Pipe i o m r
mapMake k (Ready f o p) = Ready f o $ mapMake k p
mapMake k (Need f n) = Need f $ \i -> mapMake k $ n i
mapMake _ (Done f r) = Done f r
mapMake k (Make f m) = Make f . k $ mapMake k `liftM` m