module Control.Object.Mortal (
Mortal(..),
mortal,
mortal_,
runMortal,
immortal,
apprisesOf,
apprises,
apprise
) where
import Control.Object.Object
#if !MIN_VERSION_base(4,8,0)
import Control.Applicative
#endif
import Control.Monad.Trans.Either
import Control.Monad
import Control.Monad.Trans.Class
import Control.Monad.Trans.State.Strict
import Control.Monad.Trans.Writer.Strict
import Data.Monoid
import Data.Witherable
import Data.Tuple (swap)
import Control.Arrow ((***))
import Unsafe.Coerce
newtype Mortal f g a = Mortal { unMortal :: Object f (EitherT a g) }
instance (Functor m, Monad m) => Functor (Mortal f m) where
fmap f (Mortal obj) = Mortal (obj @>>^ bimapEitherT f id)
instance (Functor m, Monad m) => Applicative (Mortal f m) where
pure = return
(<*>) = ap
instance Monad m => Monad (Mortal f m) where
return a = mortal $ const $ left a
m >>= k = mortal $ \f -> lift (runEitherT $ runMortal m f) >>= \r -> case r of
Left a -> runMortal (k a) f
Right (x, m') -> return (x, m' >>= k)
instance MonadTrans (Mortal f) where
lift m = mortal $ const $ EitherT $ liftM Left m
mortal :: Monad m => (forall x. f x -> EitherT a m (x, Mortal f m a)) -> Mortal f m a
mortal f = unsafeCoerce f `asTypeOf` Mortal (Object (fmap (fmap unMortal) . f))
runMortal :: Monad m => Mortal f m a -> f x -> EitherT a m (x, Mortal f m a)
runMortal = unsafeCoerce `asTypeOf` ((fmap (fmap Mortal) . ) . runObject . unMortal)
mortal_ :: Object f (EitherT () g) -> Mortal f g ()
mortal_ = Mortal
immortal :: Monad m => Object f m -> Mortal f m x
immortal obj = Mortal (obj @>>^ lift)
apprisesOf :: (Monad m, Monoid r) => ((Mortal f m b -> WriterT r m (Maybe (Mortal f m b))) -> s -> WriterT r m s)
-> f a -> (a -> r) -> (b -> r) -> StateT s m r
apprisesOf l f p q = StateT $ \t -> liftM swap $ runWriterT $ flip l t
$ \obj -> WriterT $ runEitherT (runMortal obj f) >>= \case
Left r -> return (Nothing, q r)
Right (x, obj') -> return (Just obj', p x)
apprises :: (Witherable t, Monad m, Applicative m, Monoid r) => f a -> (a -> r) -> (b -> r) -> StateT (t (Mortal f m b)) m r
apprises = apprisesOf wither
apprise :: (Witherable t, Monad m, Applicative m) => f a -> StateT (t (Mortal f m r)) m ([a], [r])
apprise f = fmap (flip appEndo [] *** flip appEndo [])
$ apprises f (\a -> (Endo (a:), mempty)) (\b -> (mempty, Endo (b:)))