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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Contracted exceptions for Ada
Newsgroups: comp.lang.ada
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Date: Sun, 9 Dec 2007 12:02:48 +0100
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Date: 2007-12-09T12:02:50+01:00
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On Sun, 09 Dec 2007 05:22:44 -0500, Stephen Leake wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> On Fri, 7 Dec 2007 21:30:05 -0600, Randy Brukardt wrote:
>>
>>> Another one is what to do if a contract is violated. The obvious answer of
>>> raising Program_Error doesn't do anything other than lose information about
>>> an exception, so that isn't very satisfying.
>>
>> Yes, in my view exception contracts have to be static. 
> 
> The only way to statically enforce exception contracts is to use SPARK
> Ada (http://www.praxis-his.com/sparkada/). SPARK Ada does do exactly
> that (among other things); it also signficantly restricts the Ada
> language to a manageable subset.

(I doubt that limitations of SPARK are caused by contracted exceptions. It
just does right what Ada didn't.)

> So if you like exception contracts, use SPARK Ada.
> 
> If you like all the things SPARK Ada leaves out (I don't have the
> current list handy; it doesn't seem to be on the web site), use
> standard Ada.

This does not answer the questions, which are two:

1. Are contracted exceptions any good?
(If they are not then SPARK isn't as well)

2. Can Ada have them?
(If not then why SPARK does?)

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