Hi all, Further to earlier discussion on this topic, I've just released a first version of this package to hackage: http://hackage.haskell.org/package/simple-observer It is a fairly simple implementation of subject/observer which I've recently used to good effect in an GUI written using wxHaskell. Here's a blog post discussing it further and giving a simple example of use: http://gimbo.org.uk/blog/2009/11/12/simple-observers-in-haskell/ Many thanks for the earlier comments, even if they haven't resulted in any changes (yet?). Best regards, -Andy