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From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?=
 =?utf-8?Q?=29?=
 <yannick_duchene@yahoo.fr>
Newsgroups: comp.lang.ada
Subject: Re: Processing array subsections, a newbie question.
Date: Sat, 12 Jun 2010 21:38:50 +0200
Organization: Ada At Home
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Date: 2010-06-12T21:38:50+02:00
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Le Sat, 12 Jun 2010 21:11:33 +0200, Peter C. Chapin <pcc482719@gmail.com=
>  =

a =C3=A9crit:
> Ok        : Boolean :=3D True;
> Index_Fst : Natural :=3D Buffer'First;
> Index_Lst : Natural;
> ...
>
> while Ok and Index_Fst <=3D Buffer'Last loop
>   Do_Something(Buffer, Index_Fst, Index_Lst, Ok);
>   Index_Fst :=3D Index_Lst + 1;
> end loop;
>
> The problem with this code is that the assignment to Index_Fst inside =
 =

> the loop
> might raise Constraint_Error if Index_Lst =3D Buffer'Last after  =

> Do_Something
I know this, this is a very common problem too me : I simply use an =E2=80=
=9Cexit  =

when not Condition=E2=80=9D before the increment. This requires a little=
 redesign,  =

like wrapping the look in a =E2=80=9Cif Condition then=E2=80=9D.

Sometime, to have something clean from the logical point of view, you mu=
st  =

have something which is =E2=80=9Cless=E2=80=9D visually clean... or I wo=
uld better say,  =

less short and more explicitly handles some cases which are merged  =

otherwise.

Do you think this idea is good enough ? Does it match your requirements =
?

-- =

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.