Reference types

Ashley Yakeley [email protected]
Tue, 5 Feb 2002 11:43:13 -0800


At 2002-02-05 07:50, Simon Peyton-Jones wrote:

>	data Ref m a	-- References in monad m, values of type a
etc.

You might be interested in:

<http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/*checkout*/jvm-bridge/sourc
e/Haskell/Ref.hs?rev=HEAD&content-type=text/plain>

	data Ref m a = MkRef
		{
		get :: m a,
		set :: a -> m (),
		modify :: (a -> a) -> m ()
		};

JVM-Bridge uses Refs for fields in Java classes. The monads in question 
are of type "(IsJVMMonad m) => m".

As a general rule, if your class has a lot of members of the form "a -> 
b", where the a's are all the same, it's a clue to consider using a data 
type instead.

-- 
Ashley Yakeley, Seattle WA