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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: and then... (a curiosity)
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Date: Thu, 4 Sep 2008 17:42:04 +0200
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Date: 2008-09-04T17:42:04+02:00
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On Thu, 4 Sep 2008 17:16:05 +0200, Karel Th�nissen wrote:

> Just to be nitpicking: coming from a DbC-background, a division by zero 
> should raise a *violation* of contract, not an exception. A violation indeed 
> is a contraction with the explicitly stated contracts. After a violation 
> anything goes.

This contradiction is not the contradiction T of multi-valued logic.
Violation of DbC is a contradiction in the interpretation of a formula F.
It tells that F is incorrect <=> F is not a language statement. On the
contrary, the symbol T (or an exception propagation) is itself correct, it
is a language term.

Whether division by zero is illegal (a contract violation) or T
(exceptional), is a question of type language/design. Ada uses the latter,
because the former would make illegal programs compilable, which nobody
wants.
 
> *Exceptions* should be used for things that can be expected, but that should 
> be very rare and that are to hard to handle using standard control 
> structures. Think of printers that break down, or network failures.

Yes.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de