{--
JVM-Bridge -- bridge from FP languages and others to the Java VM
Copyright (C) 2001 Ashley Yakeley <ashley@semantic.org>

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
--}

module Control.Monad.Reference where
	{
	

	-- MonadReference
	
	class (Monad m) => MonadReference m r where
		{
		get :: forall a. r a -> m a;
		set :: forall a. r a -> a -> m ();
		};

	modify :: (MonadReference m r) => r a -> (a -> m a) -> m ();
	modify ref ama = do
		{
		a <- get ref;
		a' <- ama a;
		set ref a';
		};


	-- SingleMonadReference
	
	class (MonadReference m r) => SingleMonadReference m r | r -> m;
	
	get1 :: (SingleMonadReference m r) => r a -> m a;
	get1 = get;
	
	set1 :: (SingleMonadReference m r) => r a -> a -> m ();
	set1 = set;
	

	-- Ref	
	
	data Ref m a = MkRef
		{
		getRef :: m a,
		setRef :: a -> m ()
		};

	instance (Monad m) => MonadReference m (Ref m) where
		{
		get = getRef;
		set = setRef;
		};

	instance (Monad m) => SingleMonadReference m (Ref m);

	toRef :: (MonadReference m r) => r a -> Ref m a;
	toRef r = MkRef (get r) (set r);

	refBind :: (MonadReference m r) => (m a) -> (a -> r b) -> Ref m b;
	refBind ma arb = MkRef
		(			ma >>= (\a -> get		(arb a)		))
		(\b ->		ma >>= (\a -> set		(arb a) b	));
	
--	ioRef r = MkRef (readIORef r) (writeIORef r);
	}