Have you read Wouter Swierstra's "Data Types A La Carte" [1]? Whether it uses basic and easy parts of Haskell depends on your mindset. You need to wrap your head around the fixpoint. It requires at least the MultiParamTypeClasses language extension. Regards, Roel 1 - http://www.cs.nott.ac.uk/~wss/Publications/DataTypesALaCarte.pdf On Mon, Aug 16, 2010 at 12:17 PM, Patrick Browne wrote:

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

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