Hi, The expression problem [1] can be described as the ability to add new variants (either constructors or methods) to a data type without changing the existing code. The Haskell and OO language issues are well described at [1] It seems that the expression problem does not exist in Maude[2]. My question is: Using basic and easy parts of the Haskell, does Haskell currently handle the expression problem. In other words I would like to avoid demanding and sophisticated coding techniques or non-standard Haskell extensions (i.e. it should be easy for the average programmer to use). If there is a simple solution could you please point me to an example. Thanks, Pat [1] Dr. Ralf Laemmel http://channel9.msdn.com/shows/Going+Deep/C9-Lectures-Dr-Ralf-Laemmel-Advanc... [2]http://lists.cs.uiuc.edu/pipermail/maude-help/2010-January/000336.html This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie