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From: Pierre Weis <pierre.weis@inria.fr>
Message-Id: <200210291032.LAA27077@pauillac.inria.fr>
Subject: Re: [Caml-list] On the equality of functional values
In-Reply-To: <3DBCD600.2000307@baretta.com> from Alessandro Baretta at "Oct 28, 102 07:15:28 am"
To: alex@baretta.com (Alessandro Baretta)
Date: Tue, 29 Oct 2002 11:32:02 +0100 (MET)
Cc: caml-list@inria.fr
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> David Monniaux wrote:
> > On Sun, 27 Oct 2002, Alessandro Baretta wrote:
> > 
> > 
> > If I remember well, = is implemented by doing first a == (equality of
> > pointers) test, and returning true if that test succeeds; otherwise,
> > the more complex recursive equality test is performed, which fails with
> > an exception if it encounters functional values.
> > 
> > So if x and y are the same closure, x=y succeeds and yields the true
> > value. Otherwise, it throws an exception.
> 
> This is what I suspected. I wonder if this behavior conforms 
> to specification, or if it is an incidental concequence of 
> the implementation of (=).
> 
> Alex

This is in the spec of = and ==.

This is explained in large in the FAQ:

-- What's the difference between = and == ?
   http://pauillac.inria.fr/caml/FAQ/FAQ_EXPERT-eng.html#egalite
-- How to compare functional values ?
   (Invalid_argument "equal: functional value") ?
   http://pauillac.inria.fr/caml/FAQ/FAQ_EXPERT-eng.html#egalitefonctionnelle

Best regards,

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://pauillac.inria.fr/~weis/


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