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From: Phil Thornley <phil.jpthornley@googlemail.com>
Newsgroups: comp.lang.ada
Subject: Re: Trouble cutting loops with SPARK. Advice?
Date: Sun, 7 Mar 2010 03:43:12 -0800 (PST)
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Date: 2010-03-07T03:43:12-08:00
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On 7 Mar, 11:20, Simon Wright <si...@pushface.org> wrote:
> Phil Thornley <phil.jpthorn...@googlemail.com> writes:
> > The problem is that the value of the variables that provide the loop
> > bounds (in your code the variable Characters_To_Copy) can be changed
> > within the loop, so any reference to Characters_To_Copy within an
> > assertion in the loop means the *current* value, not the value that
> > defined the loop bound.
>
> Would it have helped if Peter had said, instead of
>
> =A0 =A0 =A0 Characters_To_Copy : Line_Size_Type;
> =A0 =A0begin
> =A0 =A0 =A0 Result.Text :=3D Line_Type'(others =3D> ' ');
> =A0 =A0 =A0 if Line'Length > Max_Line_Length then
> =A0 =A0 =A0 =A0 =A0Characters_To_Copy :=3D Max_Line_Length;
> =A0 =A0 =A0 else
> =A0 =A0 =A0 =A0 =A0Characters_To_Copy :=3D Line'Length;
> =A0 =A0 =A0 end if;
>
> this:
>
> =A0 =A0 =A0 Characters_To_Copy : constant Line_Size_Type
> =A0 =A0 =A0 =A0 :=3D Line_Size_Type'Min (Line'Length, Max_Line_Length);
> =A0 =A0begin
> =A0 =A0 =A0 Result.Text :=3D Line_Type'(others =3D> ' ');
>
> And I'm sure one could eliminate the loop by proper slicing. Of course,
> that would reduce the SPARK learning experience ...

Well - he would have learned that it isn't valid SPARK :-)
(All initialization values must be static and slices aren't allowed
either)

Cheers,

Phil