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From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?=
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 <yannick_duchene@yahoo.fr>
Newsgroups: comp.lang.ada
Subject: Re: SPARK again : for-loop vs single loop - a strange case
Date: Fri, 28 May 2010 11:00:14 +0200
Organization: Ada At Home
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Date: 2010-05-28T11:00:14+02:00
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Le Fri, 28 May 2010 10:14:56 +0200, Phil Thornley  =

<phil.jpthornley@googlemail.com> a =C3=A9crit:
> You can get it back by adding L <=3D Length to the assertion.  [You
> might also need to change the test to
> exit when L >=3D Length;]
>
> It is put in there aotomatically for a 'for' loop but not for a simple=

> loop.
You're wonderful Phil! This was something near to that: I've added L <=3D=
  =

Length, it was not OK, so I though if the upper bound hypothesis was los=
t,  =

so as well was probably the one of the lower bound. So I've added L >=3D=
 1,  =

then figured that the Checked expression was not verified for L lower th=
an  =

zero, so thought if one hypothesis was required, this was this only one,=
  =

the one for the lower bound. So I removed the L <=3D Length and left L >=
=3D 1  =

only, which was shown to be enough.

Without you, I would not have been able to guess the trouble was there, =
as  =

to me, it was obvious L >=3D 1, as the type of L, which is really  =

Length_Type, has Length_Type'First =3D 1.

This is still strange in some way, as if I do L >=3D Length_Type'First, =
it  =

works.

So the Assert clause even drops implicit hypotheses about numeric type  =

bounds ? I was thinking this ones were preserved even after an Assert  =

clause.

I was pretty sure Assert was still preserving somethings, as I feel I  =

remember I have read something suggesting that in one of the Praxis's  =

documentation and in yours as well (do not remember which PDF file, and =
 =

there many to check).

> * If the code is too big to put in a message then you can send it by
> email to the address on the proof tutorials and I'll be happy to have
> a look at it.
Not too big, this was just that as I was afraid my style with SPARK may =
 =

not be good enough to be posted here. I have lot of lines of SPARK proof=
s  =

for few lines of Ada text, which may seems silly to someones... also tha=
t  =

I like to have explicit things, because it is more easy to understand an=
d  =

to track.

-- =

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.