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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: Lost in translation (with SPARK user rules)
Date: Thu, 27 May 2010 12:55:04 +0200
Organization: Ada At Home
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Date: 2010-05-27T12:55:04+02:00
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Le Thu, 27 May 2010 10:13:55 +0200, Yannick Duch=C3=AAne (Hibou57)  =

<yannick_duchene@yahoo.fr> a =C3=A9crit:
> Finally, there is a work-around: if the Simplifier expect an expressio=
n  =

> which exactly match the one provided as a user rule, and there is not =
a  =

> direct matching expression in the source, then just use Simplifier's  =

> embedded rules to prove an expression is equivalent to the one the  =

> Simplifier expect an exact match.
>
> That is, if there a user rule of the form
>
>     my_rule(1) Conclusion_1 may_be_deduced_from [Expression_1].
>
> and the source unfortunately contains only
>
>     Expression_2
>
> then try something like
>
>     --# check Expression_2 -> Intermediate_Expression(1);
>     --# check ...;
>     --# check ...;
>     --# check Intermediate_Expression(N) -> Expression_1;
>
> and here it is.
>

Unfortunately, I came into another trouble. I was trying this, and used =
 =

intermediate variables to help. But Simplifier insist on using expressio=
ns  =

instead of variables, so it can't find a match.

An example will be more expressive:

Here is an excerpt of a source (T is a modular type):

    ...
    --# check T'Pos (B) >=3D 0; -- Check #1
    --# check T'Pos (B) <=3D 1; -- Check #2
    --# check (T'Pos (B) =3D 0) or (T'Pos (B) =3D 1); -- Check #3
    ...

Here is a rule in a user rules file:

    my_rule(1): (X=3D0) or (X=3D1) may_be_deduced_from [ integer(X), X>=3D=
0, X<=3D1  =

].

And Simplifier fails to prove Check #3 ; an excerpt of the *.SIV file  =

shows why (conclusion associated to Check #3):

    C1:    bit__and(v, 1) =3D 0 or bit__and(v, 1) =3D 1 .

It replaces B with the source expression of the value of B and is thus  =

unable to find a match with the rule. By the way, it drops Check #1 and =
 =

Check #2, which does not appears at all in the hypotheses list (possibly=
  =

it seems to much obvious to Simplifier).

I've tried to use an Assert instead of a Check, this did not change  =

anything.

So if Simplifier requires an exact match to user rules, is there a way t=
o  =

avoid the simplifier to brake any attempt to prove an expression match a=
  =

rule ?

-- =

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.