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{-
Copyright 2009 Mario Blazevic
This file is part of the Streaming Component Combinators (SCC) project.
The SCC project is free software: you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.
SCC is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
License for more details.
You should have received a copy of the GNU General Public License
along with SCC. If not, see <http://www.gnu.org/licenses/>.
-}
-- | Module "Trampoline" defines the pipe computations and their basic building blocks.
{-# LANGUAGE ScopedTypeVariables, Rank2Types, MultiParamTypeClasses,
TypeFamilies, KindSignatures, FlexibleContexts, NoMonadFailDesugaring,
FlexibleInstances, OverlappingInstances, UndecidableInstances
#-}
{- Somewhere we get:
Wanted: AncestorFunctor (EitherFunctor a (TryYield a)) d
This should not reduce because of overlapping instances
If it (erroneously) does reduce, via dfun2 we get
Wanted: Functor (EitherFunctor a (TryYield a)
Functor d'
Functor d
d ~ EitherFunctor d' s
AncestorFunctor (EitherFunctor a (TryYield a) d'
And that gives an infinite loop in the type checker!
-}
module Main where
import Control.Monad (liftM, liftM2, when, ap)
-- import Control.Monad.Identity
import Debug.Trace (trace)
-------------
class (Functor a, Functor d) => AncestorFunctor a d where
liftFunctor :: a x -> d x
-- dfun 1
instance Functor a => AncestorFunctor a a where
liftFunctor = trace "liftFunctor id" . id
-- dfun 2
instance ( Functor a
, Functor d'
, Functor d
, d ~ EitherFunctor d' s
, AncestorFunctor a d')
=> AncestorFunctor a d where
liftFunctor = LeftF . (trace "liftFunctor other" . liftFunctor :: a x -> d' x)
-------------
newtype Identity a = Identity { runIdentity :: a }
instance Functor Identity where
fmap = liftM
instance Applicative Identity where
pure = return
(<*>) = ap
instance Monad Identity where
return a = Identity a
m >>= k = k (runIdentity m)
newtype Trampoline m s r = Trampoline {bounce :: m (TrampolineState m s r)}
data TrampolineState m s r = Done r | Suspend! (s (Trampoline m s r))
instance (Monad m, Functor s) => Functor (Trampoline m s) where
fmap = liftM
instance (Monad m, Functor s) => Applicative (Trampoline m s) where
pure = return
(<*>) = ap
instance (Monad m, Functor s) => Monad (Trampoline m s) where
return x = Trampoline (return (Done x))
t >>= f = Trampoline (bounce t >>= apply f)
where apply f (Done x) = bounce (f x)
apply f (Suspend s) = return (Suspend (fmap (>>= f) s))
data Yield x y = Yield! x y
instance Functor (Yield x) where
fmap f (Yield x y) = trace "fmap yield" $ Yield x (f y)
data Await x y = Await! (x -> y)
instance Functor (Await x) where
fmap f (Await g) = trace "fmap await" $ Await (f . g)
data EitherFunctor l r x = LeftF (l x) | RightF (r x)
instance (Functor l, Functor r) => Functor (EitherFunctor l r) where
fmap f v = trace "fmap Either" $
case v of
LeftF l -> trace "fmap LeftF" $ LeftF (fmap f l)
RightF r -> trace "fmap RightF" $ RightF (fmap f r)
type TryYield x = EitherFunctor (Yield x) (Await Bool)
suspend :: (Monad m, Functor s) => s (Trampoline m s x) -> Trampoline m s x
suspend s = Trampoline (return (Suspend s))
yield :: forall m x. Monad m => x -> Trampoline m (Yield x) ()
yield x = suspend (Yield x (return ()))
await :: forall m x. Monad m => Trampoline m (Await x) x
await = suspend (Await return)
tryYield :: forall m x. Monad m => x -> Trampoline m (TryYield x) Bool
tryYield x = suspend (LeftF (Yield x (suspend (RightF (Await return)))))
canYield :: forall m x. Monad m => Trampoline m (TryYield x) Bool
canYield = suspend (RightF (Await return))
liftBounce :: Monad m => m x -> Trampoline m s x
liftBounce = Trampoline . liftM Done
fromTrampoline :: Monad m => Trampoline m s x -> m x
fromTrampoline t = bounce t >>= \(Done x)-> return x
runTrampoline :: Monad m => Trampoline m Maybe x -> m x
runTrampoline = fromTrampoline
coupleNestedFinite :: (Functor s, Monad m) =>
Trampoline m (EitherFunctor s (TryYield a)) x
-> Trampoline m (EitherFunctor s (Await (Maybe a))) y -> Trampoline m s (x, y)
coupleNestedFinite t1 t2 =
trace "bounce start" $
liftBounce (liftM2 (,) (bounce t1) (bounce t2))
>>= \(s1, s2)-> trace "bounce end" $
case (s1, s2)
of (Done x, Done y) -> return (x, y)
(Done x, Suspend (RightF (Await c2))) -> coupleNestedFinite (return x) (c2 Nothing)
(Suspend (RightF (LeftF (Yield _ c1))), Done y) -> coupleNestedFinite c1 (return y)
(Suspend (RightF (LeftF (Yield x c1))), Suspend (RightF (Await c2))) -> coupleNestedFinite c1 (c2 $ Just x)
(Suspend (RightF (RightF (Await c1))), Suspend s2@(RightF Await{})) -> coupleNestedFinite (c1 True) (suspend s2)
(Suspend (RightF (RightF (Await c1))), Done y) -> coupleNestedFinite (c1 False) (return y)
(Suspend (LeftF s), Done y) -> suspend (fmap (flip coupleNestedFinite (return y)) s)
(Done x, Suspend (LeftF s)) -> suspend (fmap (coupleNestedFinite (return x)) s)
(Suspend (LeftF s1), Suspend (LeftF s2)) -> suspend (fmap (coupleNestedFinite $ suspend $ LeftF s1) s2)
(Suspend (LeftF s1), Suspend (RightF s2)) -> suspend (fmap (flip coupleNestedFinite (suspend $ RightF s2)) s1)
(Suspend (RightF s1), Suspend (LeftF s2)) -> suspend (fmap (coupleNestedFinite (suspend $ RightF s1)) s2)
local :: forall m l r x. (Monad m, Functor r) => Trampoline m r x -> Trampoline m (EitherFunctor l r) x
local (Trampoline mr) = Trampoline (liftM inject mr)
where inject :: TrampolineState m r x -> TrampolineState m (EitherFunctor l r) x
inject (Done x) = Done x
inject (Suspend r) = Suspend (RightF $ fmap local r)
out :: forall m l r x. (Monad m, Functor l) => Trampoline m l x -> Trampoline m (EitherFunctor l r) x
out (Trampoline ml) = Trampoline (liftM inject ml)
where inject :: TrampolineState m l x -> TrampolineState m (EitherFunctor l r) x
inject (Done x) = Done x
inject (Suspend l) = Suspend (LeftF $ fmap out l)
liftOut :: forall m a d x. (Monad m, Functor a, AncestorFunctor a d) => Trampoline m a x -> Trampoline m d x
liftOut (Trampoline ma) = trace "liftOut" $ Trampoline (liftM inject ma)
where inject :: TrampolineState m a x -> TrampolineState m d x
inject (Done x) = Done x
inject (Suspend a) = trace "inject suspend" $ Suspend (liftFunctor $ trace "calling fmap" $
fmap liftOut (trace "poking a" a))
data Sink (m :: * -> *) a x =
Sink {put :: forall d. (AncestorFunctor (EitherFunctor a (TryYield x)) d) => x -> Trampoline m d Bool,
canPut :: forall d. (AncestorFunctor (EitherFunctor a (TryYield x)) d) => Trampoline m d Bool}
newtype Source (m :: * -> *) a x =
Source {get :: forall d. (AncestorFunctor (EitherFunctor a (Await (Maybe x))) d) => Trampoline m d (Maybe x)}
pipe :: forall m a x r1 r2. (Monad m, Functor a) =>
(Sink m a x -> Trampoline m (EitherFunctor a (TryYield x)) r1)
-> (Source m a x -> Trampoline m (EitherFunctor a (Await (Maybe x))) r2) -> Trampoline m a (r1, r2)
pipe producer consumer = coupleNestedFinite (producer sink) (consumer source) where
sink = Sink {put= liftOut . (local . tryYield :: x -> Trampoline m (EitherFunctor a (TryYield x)) Bool),
canPut= liftOut (local canYield :: Trampoline m (EitherFunctor a (TryYield x)) Bool)} :: Sink m a x
source = Source (liftOut (local await :: Trampoline m (EitherFunctor a (Await (Maybe x))) (Maybe x))) :: Source m a x
pipeProducer sink = do put sink 1
(c, d) <- pipe
(\sink'-> do put sink' 2
put sink 3
put sink' 4
return 5)
(\source'-> do Just n <- get source'
put sink n
put sink 6
return n)
put sink c
put sink d
return (c, d)
testPipe = print $
runIdentity $
runTrampoline $
do (a, b) <- pipe
pipeProducer
(\source-> do Just n1 <- get source
Just n2 <- get source
Just n3 <- get source
return (n1, n2, n3))
return (a, b)
main = testPipe
|
