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[Caml-list] User-defined equality on types?
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Date: -- (:)
From: Andreas Rossberg <rossberg@p...>
Subject: Re: [Caml-list] User-defined equality on types?
Brian Rogoff wrote:
> 
> On Mon, 23 Apr 2001, Xavier Leroy wrote:
> > > I'd like to suggest allowing the user to define a chosen interpretation
> > > of the equality symbol, and perhaps the polymorphic orderings too, on
> > > each new (maybe just abstract) data type. This seems natural in the
> > > context of abstract data types with non-canonical representation, giving
> > > a kind of quotient type. Has this ever been considered?
> >
> > Yes.  This was one of the first motivations for Haskell type classes,
> > I believe.
> 
> Would the proposed generic polymorphism extension solve this problem?

Probably not, because unlike type classes generic functions are closed
and do not allow adding cases for new types later on.

-- 
Andreas Rossberg, rossberg@ps.uni-sb.de

"Computer games don't affect kids.
 If Pac Man affected us as kids, we would all be running around in
 darkened rooms, munching pills, and listening to repetitive music."
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