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Date: Sun, 09 Aug 2009 15:55:07 +0200
From: Alain Frisch <alain@frisch.fr>
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To: ivan chollet <ivan.chollet@free.fr>
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Re: ocaml sefault in bytecode: unanswered questions
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X-Spam: no; 0.00; frisch:01 frisch:01 ocaml:01 bytecode:01 pervasives:01 recursive:01 2009:98 equality:01 equality:01 wrote:01 caml-list:01 alain:01 alain:01 functional:02 traversal:03 

On 8/9/2009 2:06 PM, ivan chollet wrote:
> I would have thought physical equality implies structural equality, but
> it doesn’t seem like it.
>
> Can you please explain to me what’s wrong there?

There are two modes for the generic comparison. The total mode 
(Pervasives.compare) creates a total ordering between values (except for 
functional values and custom blocks with no comparison function) and 
uses physical equality as a shortcut to cut the recursive traversal of 
sub-values. The non-total mode (used by the operators = < > <= >=) has a 
different behavior for NaN values ([nan <= x], [x <= nan], and [nan = x] 
all return false, including when x is nan) and does not use the physical 
equality shortcut (so that [let x = (nan, nan) in x = x] returns false).

-- Alain