Re: Strategies with SPARK which does not support exceptions

[mockturtle <framefritti@gmail.com>]

On Jun 18, 10:49 am, Martin <martin.do...@btopenworld.com> wrote:
> (snip)
> > OK := True;
> > loop
> >    Some complicated code that might set OK;
> >    exit when not OK;
> >    Some more complicated code that might set OK;
> >    exit when not OK;
> >    Some more code;
> >    exit when True;
> > end loop;
>
> > :-)
>
> > Cheers,
>
> > Phil
>
> No there's a fancy 'goto'! :-)
>
> -- Martin

Well, I do not know if 'goto's are allowed in SPARK, but that is the
solution that sometimes I use when I need to write code in the-
language-whose-name-is-a-single-letter :-).  I know that it could
sound heretical, but this is one of the two cases where, I believe,
using goto is not so bad.  I am thinking something like

procedure Very_Complex_Stuff (OK : out Boolean) is
begin
  OK := True; -- Be optimistic :-)
  Open_some_file (OK);
  if not OK then
    goto Exit_now;
  end if;

  Allocate_Some_Memory (OK);
  if not OK then
    goto Undo_Open;
  end if;

  Contact_DB (OK);
  if not OK then
    goto Undo_Mem;
  end if;

  goto Exit_Now;

<<Undo_Mem>>
   Deallocate_Memory;

<<Undo_Open>>
   Close_File;

<<Exit_Now>>
end;

I agree that this will not win the prize for the best code ever, but
if you choose your labels with care it can turn out an acceptable
solution.