From: skaller <skaller@users.sourceforge.net>
To: Fernando Alegre <fernando@cc.gatech.edu>
Cc: Christophe TROESTLER <Christophe.Troestler@umh.ac.be>,
caml-list@inria.fr
Subject: Re: [Caml-list] Equality of functional values
Date: Wed, 31 Jan 2007 10:13:42 +1100 [thread overview]
Message-ID: <1170198822.6391.110.camel@rosella.wigram> (raw)
In-Reply-To: <20070130220557.GD15659@gaia.cc.gatech.edu>
On Tue, 2007-01-30 at 17:05 -0500, Fernando Alegre wrote:
> There are two separate notions of equality mixed together.
> My point is, should "OCaml polymorphic equality" be the
> same concept at "IEEE equality"?
No, this is not possible. x <> x is the IEEE test for a NaN,
and cannot possibly be used in a structural equality
test which is primarily required for inserting data into
containers: you'd have a Set in which after inserting
a value the value wasn't in the Set!
> Why not wish for three separate operators (=,== and =.)?
What about abstract types?
The bottom line is: you can always write your own comparison
functions and use them with modular functors (extensionally
polymorphic), you can't get a single coherent intensionally
polymorphic equality concept because programs are always using
representations of value rather than the mathematical values.
It is a pity we don't have G'Caml around: it may provide
a convenient way to mix user defined equality with
Ocaml's run time driven polymorphic structural equality.
--
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net
next prev parent reply other threads:[~2007-01-30 23:13 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-29 21:04 Simon Frost
2007-01-29 21:11 ` [Caml-list] " Tom
2007-01-29 21:23 ` Brian Hurt
2007-01-29 21:59 ` Gerd Stolpmann
2007-01-30 8:17 ` Christophe Raffalli
2007-01-30 8:45 ` David MENTRE
2007-01-30 13:24 ` Andrej Bauer
2007-01-30 13:55 ` skaller
2007-01-30 14:21 ` Brian Hurt
2007-01-30 15:21 ` Jeff Polakow
2007-01-30 15:49 ` Jacques Carette
2007-01-30 17:23 ` Chris King
2007-01-30 20:18 ` Tom
2007-01-30 20:30 ` Gerd Stolpmann
2007-01-30 20:41 ` Fernando Alegre
2007-01-30 21:01 ` Christophe TROESTLER
2007-01-30 21:08 ` Tom
2007-01-30 21:46 ` Christophe TROESTLER
2007-01-30 22:05 ` Fernando Alegre
2007-01-30 23:13 ` skaller [this message]
2007-01-30 23:06 ` Andrej Bauer
2007-01-31 0:15 ` Jacques Carette
2007-01-31 7:03 ` Stefan Monnier
2007-01-31 12:54 ` [Caml-list] " Jacques Carette
2007-01-31 0:15 ` [Caml-list] " skaller
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