module Data.SouSiT.Sink (
Sink(..),
SinkStatus(..),
closeSink,
input,
inputOr,
inputMap,
inputMaybe,
skip,
appendSink,
(=||=),
feedList,
liftSink,
contSink,
contSink',
doneSink,
doneSink',
actionSink,
openCloseActionSink,
maybeSink
) where
import Data.Monoid
import Control.Applicative
import Control.Monad
data Sink i m r = Sink { sinkStatus :: m (SinkStatus i m r) }
data SinkStatus i m r = Cont (i -> m (Sink i m r)) (m r)
| Done (m r)
instance Monad m => Functor (Sink i m) where
fmap f (Sink st) = Sink (liftM mp st)
where mp (Done r) = Done (liftM f r)
mp (Cont nf cf) = Cont (liftM (fmap f) . nf) (liftM f cf)
instance Monad m => Monad (Sink i m) where
return a = doneSink $ return a
(Sink st) >>= f = Sink (st >>= mp)
where mp (Done r) = liftM f r >>= sinkStatus
mp (Cont nf cf) = return $ Cont (liftM (>>= f) . nf) (cf >>= closeSink . f)
instance Monad m => Applicative (Sink i m) where
pure = return
af <*> s = do f <- af
v <- s
return (f v)
noResult :: Monad m => m a
noResult = fail "no result: not enough input"
closeSink :: Monad m => Sink i m r -> m r
closeSink (Sink st) = st >>= handle
where handle (Done r) = r
handle (Cont _ r) = r
inputOr :: Monad m => m a -> Sink a m a
inputOr = contSink' doneSink'
inputMaybe :: Monad m => Sink a m (Maybe a)
inputMaybe = inputMap (return . Just) (return Nothing)
inputMap :: Monad m => (a -> m b) -> m b -> Sink a m b
inputMap f = contSink' (doneSink . f)
input :: Monad m => Sink a m a
input = inputOr noResult
skip :: (Eq n, Num n, Monad m) => n -> Sink a m ()
skip 0 = doneSink (return ())
skip n = contSink' f (return ())
where f _ = skip (n1)
(=||=) :: (Monad m, Monoid r) => Sink a m r -> Sink a m r -> Sink a m r
(=||=) = appendSink
infixl 3 =||=
appendSink :: (Monad m, Monoid r) => Sink a m r -> Sink a m r -> Sink a m r
appendSink s1 s2 = do r1 <- s1
r2 <- s2
return $ mappend r1 r2
feedList :: Monad m => [i] -> Sink i m r -> m (Sink i m r)
feedList [] !s = return s
feedList (x:xs) !s = sinkStatus s >>= step
where step (Done r) = return s
step (Cont nf _) = nf x >>= feedList xs
contSink :: Monad m => (i -> m (Sink i m r)) -> m r -> Sink i m r
contSink next = Sink . return . Cont next
contSink' :: Monad m => (i -> Sink i m r) -> m r -> Sink i m r
contSink' next = contSink (return . next)
doneSink :: Monad m => m r -> Sink i m r
doneSink = Sink . return . Done
doneSink' :: Monad m => r -> Sink i m r
doneSink' = Sink . return . Done . return
actionSink :: Monad m => (i -> m ()) -> Sink i m ()
actionSink process = contSink step (return ())
where step i = process i >> return (actionSink process)
openCloseActionSink :: Monad m => m a -> (a -> m ()) -> (a -> i -> m ()) -> Sink i m ()
openCloseActionSink open close process = contSink first (return ())
where first i = open >>= flip step i
step rs i = process rs i >> return (contSink (step rs) (close rs))
maybeSink :: Monad m => (i -> m (Maybe r)) -> Sink i m (Maybe r)
maybeSink process = contSink step (return Nothing)
where step i = process i >>= cont
cont Nothing = return $ maybeSink process
cont result = return $ doneSink' result
liftSink :: (Monad m, Monad m') => (forall x . m x -> m' x) -> Sink i m r -> Sink i m' r
liftSink t sink = Sink $ t (sinkStatus sink >>= trans)
where trans (Done r) = return $ Done $ t r
trans (Cont nf cf) = return $ Cont nf' (t cf)
where nf' i = liftM (liftSink t) (t $ nf i)