[Haskell-cafe] expression problem

Roel van Dijk vandijk.roel at gmail.com
Mon Aug 16 06:34:44 EDT 2010

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.


1 - http://www.cs.nott.ac.uk/~wss/Publications/DataTypesALaCarte.pdf

On Mon, Aug 16, 2010 at 12:17 PM, Patrick Browne <patrick.browne at dit.ie> 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-Advanced-Functional-Programming-The-Expression-Problem/
> [2]http://lists.cs.uiuc.edu/pipermail/maude-help/2010-January/000336.html
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