Might be worth reading http://lukepalmer.wordpress.com/2010/01/24/haskell-antipattern-existential-typeclass/ Especially in the context of guis and widgets. Ben -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/beginners/attachments/20130528/93f5198b/attachment-0001.htm>