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From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?=
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Newsgroups: comp.lang.ada
Subject: Re: SPARK understand me very well... me neither
Date: Sun, 15 Aug 2010 02:45:51 +0200
Organization: Ada At Home
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Date: 2010-08-15T02:45:51+02:00
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Le Sat, 14 Aug 2010 23:50:08 +0200, Jeffrey Carter  =

<spam.jrcarter.not@spam.not.acm.org> a =C3=A9crit:
>> But what seems important to me and I would to underline, was also tha=
t
>> if I did not knew this was possible, this was because it was fr from =
my
>> mind. And this was far from my mind, because looking at it as-is, I
>> would have said =E2=80=9Cwhat does it prove ? what does it offer ?=E2=
=80=9D. In short,
>> this looks like a bad logical interface to me.
>
> It doesn't prove anything, and it's not supposed to. It's a  =

> precondition. It says, "This precondition must be true for this  =

> operation to give correct results." It is the caller's duty to meet th=
e  =

> precondition.

Reading you again, I understand I did not choose the good words. I shoul=
d  =

have said =E2=80=9Cwhat does it defines ?=E2=80=9D (like defining what a=
 valid context is,  =

in a concrete way). Otherwise yes, this does not have to prove anything,=
  =

and this can't, because nothing is provable at this level.

-- =

There is even better than a pragma Assert: a SPARK --# check.
--# check C and WhoKnowWhat and YouKnowWho;
--# assert Ada;
--  i.e. forget about previous premises which leads to conclusion
--  and start with new conclusion as premise.