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{-# LANGUAGE BangPatterns, Rank2Types, FlexibleContexts, LambdaCase, DeepSubsumption #-}
module DeepSubsumption02 where
import Data.Semigroup
-- | Finite source
type Source r s = Tap r (Maybe s)
newtype Sink t m a = Sink
{ unSink :: forall r. t m -> (a -> t m -> m r) -> m r }
-- | Mono in/out
type Converter p q r s m = Source r s (Sink (Source p q) m)
type Pipe a b m = forall r. (Monoid r, Semigroup r) => Converter r a r b m
newtype Tap r s m = Tap { unTap :: r -> m (s, Tap r s m) }
type Distiller tap r s m = Tap r s (Sink tap m)
filter :: Monad m => (a -> Bool) -> Pipe a a m
--filter f = filtering $ maybe True f
filter = filtering . maybe True
{-# INLINE filter #-}
mapAccum :: Monad m => (s -> a -> (s, b)) -> s -> Pipe a b m
--mapAccum f x = go x where
mapAccum f = go where
go s = reservingTap $ \case
Just a -> let (s', b) = f s a in return (Just b, go s')
Nothing -> return (Nothing, go s)
{-# INLINE mapAccum #-}
traverse :: (Monad m) => (a -> m b) -> Pipe a b m
-- traverse f = traversing $ Prelude.traverse f
traverse = traversing . Prelude.traverse
{-# INLINE traverse #-}
-- | Get one element preserving a request
reservingTap :: Monad m => (a -> Sink (Tap r a) m (b, Distiller (Tap r a) r b m)) -> Distiller (Tap r a) r b m
reservingTap k = Tap $ \r -> Sink $ \t cont -> do
(a, t') <- unTap t r
unSink (k a) t' cont
{-# INLINE reservingTap #-}
traversing :: (Monad m) => (a -> m b) -> Distiller (Tap r a) r b m
traversing f = go where
go = reservingTap $ \a -> do
b <- undefined $ f a
return (b, go)
{-# INLINE traversing #-}
filtering :: (Monoid r, Monad m) => (a -> Bool) -> Distiller (Tap r a) r a m
filtering f = go where
go = reservingTap $ \a -> if f a
then return (a, go)
else unTap go mempty
{-# INLINE filtering #-}
instance Functor (Sink s m) where
fmap f m = Sink $ \s k -> unSink m s (k . f)
instance Applicative (Sink s m) where
pure a = Sink $ \s k -> k a s
Sink mf <*> Sink mx = Sink
$ \s k -> mf s $ \f s' -> mx s' $ k . f
m *> k = m >>= \_ -> k
instance Monad (Sink s m) where
return = pure
{-# INLINE return #-}
m >>= k = Sink $ \s cont -> unSink m s $ \a s' -> unSink (k a) s' cont
|
