content: {-# LANGUAGE BangPatterns #-}
  
  -- modified from Control.Monad.RWS by John Meacham to be strict
  
  module Util.RWS (
  	RWS,
          runRWS,
  --	evalRWS,
  --	execRWS,
  --	mapRWS,
  --	withRWS,
  --	RWST(..),
  --	evalRWST,
  --	execRWST,
  --	mapRWST,
  --	withRWST,
  	module Control.Monad.Reader,
  	module Control.Monad.Writer,
  	module Control.Monad.State,
    ) where
  
  import Prelude
  
  import Control.Monad
  import Control.Monad.Fix
  import Control.Monad.Trans
  import Control.Monad.Reader
  import Control.Monad.Writer
  import Control.Monad.State
  
  
  
  newtype RWS r w s a = RWS { runRWS' :: r -> s -> (# a, s, w #) }
  
  runRWS :: RWS r w s a -> r -> s -> (a,s,w)
  runRWS x r s = case runRWS' x r s of
      (# a, b, c #) -> (a,b,c)
  
  instance Functor (RWS r w s) where
  	fmap f m = RWS $ \r s -> case runRWS' m r s of
  		(# a, s', w #) -> (# f a, s', w #)
  
  instance (Monoid w) => Monad (RWS r w s) where
  	return a = RWS $ \_ s -> (# a, s, mempty #)
  	m >>= k  = RWS $ \r s -> case runRWS' m r s of
  		(# a, s',  w #) -> case runRWS' (k a) r s' of
                      (# b, s'', w' #) -> let !w'' = w `mappend` w'
                          in (# b, s'', w'' #)
  
  --instance (Monoid w) => MonadFix (RWS r w s) where
  --	mfix f = RWS $ \r s -> let (a, s', w) = runRWS (f a) r s in (a, s', w)
  
  instance (Monoid w) => MonadReader r (RWS r w s) where
  	ask       = RWS $ \r s -> (# r, s, mempty #)
  	local f m = RWS $ \r s -> let !r' = f r in runRWS' m r' s
  
  instance (Monoid w) => MonadWriter w (RWS r w s) where
  	tell   w = RWS $ \_ s -> (# (), s, w #)
  	listen m = RWS $ \r s -> case runRWS' m r s of
              (# a, s', w #) -> (# (a, w), s', w #)
  	pass   m = RWS $ \r s -> case runRWS' m r s of
  		(# (a, f), s', w #) -> let !w' = f w in (# a, s', w' #)
  
  instance (Monoid w) => MonadState s (RWS r w s) where
  	get   = RWS $ \_ s -> (# s, s, mempty #)
  	put !s = RWS $ \_ _ -> (# (), s, mempty #)
  
  {-
  evalRWS :: RWS r w s a -> r -> s -> (a, w)
  evalRWS m r s = let
      (a, _, w) = runRWS m r s
      in (a, w)
  
  execRWS :: RWS r w s a -> r -> s -> (s, w)
  execRWS m r s = let
      (_, s', w) = runRWS m r s
      in (s', w)
  
  mapRWS :: ((a, s, w) -> (b, s, w')) -> RWS r w s a -> RWS r w' s b
  mapRWS f m = RWS $ \r s -> f (runRWS m r s)
  
  withRWS :: (r' -> s -> (r, s)) -> RWS r w s a -> RWS r' w s a
  withRWS f m = RWS $ \r s -> uncurry (runRWS m) (f r s)
  
  
  newtype RWST r w s m a = RWST { runRWST :: r -> s -> m (a, s, w) }
  
  instance (Monad m) => Functor (RWST r w s m) where
  	fmap f m = RWST $ \r s -> do
  		(a, s', w) <- runRWST m r s
  		return (f a, s', w)
  
  instance (Monoid w, Monad m) => Monad (RWST r w s m) where
  	return a = RWST $ \_ s -> return (a, s, mempty)
  	m >>= k  = RWST $ \r s -> do
  		(a, s', w)  <- runRWST m r s
  		(b, s'',w') <- runRWST (k a) r s'
  		return (b, s'', w `mappend` w')
  	fail msg = RWST $ \_ _ -> fail msg
  
  instance (Monoid w, MonadPlus m) => MonadPlus (RWST r w s m) where
  	mzero       = RWST $ \_ _ -> mzero
  	m `mplus` n = RWST $ \r s -> runRWST m r s `mplus` runRWST n r s
  
  instance (Monoid w, MonadFix m) => MonadFix (RWST r w s m) where
  	mfix f = RWST $ \r s -> mfix $ \ ~(a, _, _) -> runRWST (f a) r s
  
  instance (Monoid w, Monad m) => MonadReader r (RWST r w s m) where
  	ask       = RWST $ \r s -> return (r, s, mempty)
  	local f m = RWST $ \r s -> runRWST m (f r) s
  
  instance (Monoid w, Monad m) => MonadWriter w (RWST r w s m) where
  	tell   w = RWST $ \_ s -> return ((),s,w)
  	listen m = RWST $ \r s -> do
  		(a, s', w) <- runRWST m r s
  		return ((a, w), s', w)
  	pass   m = RWST $ \r s -> do
  		((a, f), s', w) <- runRWST m r s
  		return (a, s', f w)
  
  instance (Monoid w, Monad m) => MonadState s (RWST r w s m) where
  	get   = RWST $ \_ s -> return (s, s, mempty)
  	put s = RWST $ \_ _ -> return ((), s, mempty)
  
  instance (Monoid w) => MonadTrans (RWST r w s) where
  	lift m = RWST $ \_ s -> do
  		a <- m
  		return (a, s, mempty)
  
  instance (Monoid w, MonadIO m) => MonadIO (RWST r w s m) where
  	liftIO = lift . liftIO
  
  
  evalRWST :: (Monad m) => RWST r w s m a -> r -> s -> m (a, w)
  evalRWST m r s = do
      (a, _, w) <- runRWST m r s
      return (a, w)
  
  execRWST :: (Monad m) => RWST r w s m a -> r -> s -> m (s, w)
  execRWST m r s = do
      (_, s', w) <- runRWST m r s
      return (s', w)
  
  mapRWST :: (m (a, s, w) -> n (b, s, w')) -> RWST r w s m a -> RWST r w' s n b
  mapRWST f m = RWST $ \r s -> f (runRWST m r s)
  
  withRWST :: (r' -> s -> (r, s)) -> RWST r w s m a -> RWST r' w s m a
  withRWST f m = RWST $ \r s -> uncurry (runRWST m) (f r s)
  -}
  