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{-# LANGUAGE GADTs #-}
{-# LANGUAGE TupleSections #-}
{-# LANGUAGE ViewPatterns #-}
{-# LANGUAGE FlexibleContexts, FlexibleInstances #-}
module Events.Types.NDT
( NDT
, foldNDT
, cons
, fromFoldable
) where
import Data.Monoid
import Data.Foldable (foldr)
import Data.Maybe
import Data.Either
import Control.Monad
import Control.Monad.Identity
import Control.Monad.Trans
import Debug.Trace
data NDT m a where
NDTBind :: NDT m a -> (a -> NDT m b) -> NDT m b
NDTCons :: m (Maybe (a, NDT m a)) -> NDT m a
instance Show (NDT Identity a) where
show (NDTBind x _) = "Bind (" ++ show x ++ ") _"
show x = show . (\(NDTCons x) -> x) $ fmap (const ()) x
instance Functor m => Functor (NDT m) where
fmap f (NDTBind a g) = NDTBind a (fmap f . g)
fmap f (NDTCons x) = NDTCons $ fmap f' x
where
f' Nothing = Nothing
f' (Just (x, xs)) = Just (f x, fmap f xs)
instance Applicative m => Applicative (NDT m) where
pure x = NDTCons . pure $ Just (x, empty)
fs <*> xs = fs >>= (\f -> xs >>= pure . (f $))
instance Applicative m => Monad (NDT m) where
return = pure
fail = const empty
(>>=) = NDTBind
instance Monad m => Monoid (NDT m a) where
mempty = empty
mappend (NDTCons x) y'@(NDTCons y) = trace "(cons <> cons)" . NDTCons . trace "[cons <> cons]" $ maybe y (\(x, xs) -> return $ Just (x, xs <> y')) =<< x
mappend (NDTBind x f) (NDTBind y g) = trace "(bind <> bind)" $ NDTBind (fmap Left x <> fmap Right y) (either f g)
mappend x@(NDTBind _ _) y = trace "(bind <>)" $ x <> NDTBind y return
mappend x y@(NDTBind _ _) = trace "(<> bind)" $ NDTBind x return <> y
instance MonadTrans NDT where
lift = NDTCons . fmap Just . fmap (,empty)
empty :: Applicative m => NDT m a
empty = NDTCons $ pure Nothing
cons :: Applicative m => a -> NDT m a -> NDT m a
cons x xs = NDTCons . pure $ Just (x, xs)
foldNDT :: (Monoid a, Monad m) => (a -> m Bool) -> NDT m a -> m a
foldNDT sel = fmap snd . foldNDT' sel
foldNDT' :: (Monoid a, Monad m) => (a -> m Bool) -> NDT m a -> m (Any, a)
-- ^ Evaluate depth-first, pruning leaves under the assumption that the selection predicate is monotonic on siblings
foldNDT' sel (NDTCons mx) = do
mx' <- mx
case mx' of
Nothing -> return mempty
Just (x, mxs) -> do
continue <- sel x
case trace ("(cons "++ show continue ++ ")") continue of
False -> return (Any True, mempty)
True -> ((Any True, x) <>) <$> foldNDT' sel mxs
foldNDT' sel (NDTBind (NDTCons x) f) = trace "(bind cons)" $ do
x' <- x
case x' of
Nothing -> return mempty
Just (x'', xs) -> do -- foldNDT' sel . NDTCons $ Just . (, NDTBind xs f) . snd <$> foldNDT' sel (f x'')
(productive, x3) <- foldNDT' sel $ f x''
continue <- sel x3
case trace ("(bind cons " ++ show (productive, continue) ++ ")") $ continue || not (getAny productive) of
False -> return mempty
True -> ((mempty, x3) <>) <$> foldNDT' sel (NDTBind xs f)
foldNDT' sel (NDTBind (NDTBind x g) f) = trace "(bind bind)" . foldNDT' sel $ NDTBind x (f <=< g)
fromFoldable :: (Foldable f, Monad m) => f a -> NDT m a
fromFoldable = foldr cons empty
|
