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From: Phil Thornley <phil.jpthornley@googlemail.com>
Newsgroups: comp.lang.ada
Subject: Re: Workaround for invariant SPARK condition
Date: Thu, 25 Jun 2009 00:48:01 -0700 (PDT)
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Date: 2009-06-25T00:48:01-07:00
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On 25 June, 00:03, xorque <xorquew...@googlemail.com> wrote:
> Hello.
>
> I have a piece of code that does this:
>
> function Check_Support (Request : in Request_t) return Boolean is
> begin
> =A0 return Request /=3D Unsupported;
> end Check_Support;
>
> I'm using it in some code:
>
> if Check_Support (Request_Push) then
> =A0 ...
> end if;
>
> Request_Push is a compile-time constant with an implementation-defined
> value. Given that the value is detected at compile-time, SPARK thinks
> the
> condition is invariant.
>
> Is there some way I can tell SPARK that this condition isn't actually
> invariant,
> even though it appears to be?

You could turn it into a variable, but then it would infiltrate into
all the annotations, which you probably don't want.

This is the sort of problem that the accept annotation is there for:
   --# accept F, 22, "Value is implementation defined.";
   if Check_Support (Request_Push) then
   --# end accept;

Phil Thornley