> From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > Richard A. O'Keefe > > On 21 May 2008, at 9:25 am, Conal Elliott wrote: > > I think the practice of constraint in type definitions is > generally > > discouraged, > > Is this true? If so, why? > If I have a data type that simply doesn't make sense unless > some of the > type variables belong to certain classes, _shouldn't_ that be stated > clearly in the declaration rather than hidden elsewhere?
I recall this from Graham Klyne, but I think his use case might be a bit different: http://www.ninebynine.org/Software/Learning-Haskell-Notes.html#type-clas ses-and-data I don't know all the pros and cons (are there pros, other than the documentation argument you gave?). I think: 1. adding the constraint has some costs, and very few benefits 2. nobody does it much, if at all. Probably for the first reason. Alistair ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. ***************************************************************** _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
