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From: mockturtle <framefritti@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Strategies with SPARK which does not support exceptions
Date: Fri, 18 Jun 2010 10:16:49 -0700 (PDT)
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Date: 2010-06-18T10:16:49-07:00
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On Jun 18, 10:49=A0am, Martin <martin.do...@btopenworld.com> wrote:
> (snip)
> > OK :=3D True;
> > loop
> > =A0 =A0Some complicated code that might set OK;
> > =A0 =A0exit when not OK;
> > =A0 =A0Some more complicated code that might set OK;
> > =A0 =A0exit when not OK;
> > =A0 =A0Some more code;
> > =A0 =A0exit 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 :=3D 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.