module Control.Monad.Trans.List (
ListT(..),
mapListT,
liftCallCC,
liftCatch,
) where
import Control.Monad.IO.Class
import Control.Monad.Signatures
import Control.Monad.Trans.Class
import Data.Functor.Classes
import Control.Applicative
import Control.Monad
import Data.Foldable (Foldable(foldMap))
import Data.Traversable (Traversable(traverse))
newtype ListT m a = ListT { runListT :: m [a] }
instance (Eq1 m, Eq a) => Eq (ListT m a) where
ListT x == ListT y = eq1 x y
instance (Ord1 m, Ord a) => Ord (ListT m a) where
compare (ListT x) (ListT y) = compare1 x y
instance (Read1 m, Read a) => Read (ListT m a) where
readsPrec = readsData $ readsUnary1 "ListT" ListT
instance (Show1 m, Show a) => Show (ListT m a) where
showsPrec d (ListT m) = showsUnary1 "ListT" d m
instance (Eq1 m) => Eq1 (ListT m) where eq1 = (==)
instance (Ord1 m) => Ord1 (ListT m) where compare1 = compare
instance (Read1 m) => Read1 (ListT m) where readsPrec1 = readsPrec
instance (Show1 m) => Show1 (ListT m) where showsPrec1 = showsPrec
mapListT :: (m [a] -> n [b]) -> ListT m a -> ListT n b
mapListT f m = ListT $ f (runListT m)
instance (Functor m) => Functor (ListT m) where
fmap f = mapListT $ fmap $ map f
instance (Foldable f) => Foldable (ListT f) where
foldMap f (ListT a) = foldMap (foldMap f) a
instance (Traversable f) => Traversable (ListT f) where
traverse f (ListT a) = ListT <$> traverse (traverse f) a
instance (Applicative m) => Applicative (ListT m) where
pure a = ListT $ pure [a]
f <*> v = ListT $ (<*>) <$> runListT f <*> runListT v
instance (Applicative m) => Alternative (ListT m) where
empty = ListT $ pure []
m <|> n = ListT $ (++) <$> runListT m <*> runListT n
instance (Monad m) => Monad (ListT m) where
return a = ListT $ return [a]
m >>= k = ListT $ do
a <- runListT m
b <- mapM (runListT . k) a
return (concat b)
fail _ = ListT $ return []
instance (Monad m) => MonadPlus (ListT m) where
mzero = ListT $ return []
m `mplus` n = ListT $ do
a <- runListT m
b <- runListT n
return (a ++ b)
instance MonadTrans ListT where
lift m = ListT $ do
a <- m
return [a]
instance (MonadIO m) => MonadIO (ListT m) where
liftIO = lift . liftIO
liftCallCC :: CallCC m [a] [b] -> CallCC (ListT m) a b
liftCallCC callCC f = ListT $
callCC $ \ c ->
runListT (f (\ a -> ListT $ c [a]))
liftCatch :: Catch e m [a] -> Catch e (ListT m) a
liftCatch catchE m h = ListT $ runListT m
`catchE` \ e -> runListT (h e)