86 lines
2.5 KiB
Haskell
86 lines
2.5 KiB
Haskell
{-# LANGUAGE NamedFieldPuns #-}
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{-# LANGUAGE FunctionalDependencies #-}
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{-# LANGUAGE FlexibleInstances #-}
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{-# LANGUAGE FlexibleContexts #-}
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{-# LANGUAGE UndecidableInstances #-}
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{-# LANGUAGE ScopedTypeVariables #-}
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module PDF.Box (
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Box(..)
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, Index(..)
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, Maybe_(..)
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, Either_(..)
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, at
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, atAll
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, edit
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) where
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import Control.Monad.Except (ExceptT(..), runExceptT)
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import Control.Monad.Fail (MonadFail(..))
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import Control.Monad.State (MonadState(..))
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--import Control.Monad.Reader (MonadReader(..))
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import Data.Map (Map)
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import qualified Data.Map as Map (insert, lookup, member)
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import Data.OrderedMap (OrderedMap)
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import qualified Data.OrderedMap as OrderedMap (lookup, set)
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import Prelude hiding (fail)
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{-
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instance (Monad m, MonadState s m) => MonadReader s m where
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ask = get
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local f m = do
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backup <- get
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put $ f backup
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result <- m
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put backup
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return result
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-}
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newtype Index = Index Int
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newtype Maybe_ x = Maybe_ x
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newtype Either_ b x = Either_ x
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class Monad m => Box m i a b | m a i -> b where
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r :: i -> a -> m b
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w :: i -> b -> a -> m a
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at :: Box m i a b => i -> (b -> m b) -> a -> m a
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at i f a = r i a >>= f >>= flip (w i) a
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atAll :: (Traversable t, Monad m, Box m i a (t b)) => i -> (b -> m b) -> a -> m a
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atAll i f = at i $ (mapM f)
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edit :: MonadState a m => (a -> m a) -> m ()
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edit f = get >>= f >>= put
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instance MonadFail m => Box m Index [a] a where
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r (Index i) [] = fail $ "Index out of bounds " ++ show i
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r (Index 0) (x:_) = return x
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r (Index i) (_:xs) = r (Index (i-1)) xs
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w (Index i) _ [] = fail $ "Index out of bounds " ++ show i
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w (Index 0) newX (_:xs) = return (newX:xs)
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w (Index i) newX (x:xs) = (x:) <$> w (Index (i-1)) newX xs
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instance (Ord k, MonadFail m) => Box m k (Map k a) a where
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r k = maybe (fail "Unknown key") return . Map.lookup k
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w k a aMap
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| Map.member k aMap =
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return $ Map.insert k a aMap
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| otherwise = fail "Unknown key"
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instance (Ord k, MonadFail m) => Box m k (OrderedMap k a) a where
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r k = maybe (fail "Unknown key") return . OrderedMap.lookup k
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w k a orderedMap = r k orderedMap >> return (OrderedMap.set k a orderedMap)
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instance (Monad m, Box Maybe i a b) => Box m (Maybe_ i) a (Maybe b) where
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r (Maybe_ i) = return . r i
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w (Maybe_ i) (Just b) a =
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return . maybe a id $ w i b a
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w _ _ obj = return obj
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instance (Monad m, Box (ExceptT e m) i a b) => Box m (Either_ e i) a (Either e b) where
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r (Either_ i) a = runExceptT (r i a)
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w (Either_ i) (Right b) a =
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either (const a) id <$> runExceptT (w i b a :: ExceptT e m a)
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w _ _ a = return a
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