Re: Division by zero

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On Wed, 29 Jun 2005 17:50:43 +1200, Lurker wrote:
> 
> > "Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message
> > news:wccy88ugorw.fsf@shell01.TheWorld.com...
> > 
> >> 11.6(5) is all about run time effects.  If divide by zero were illegal
> >> (which means at compile time), then 11.6 would not apply.
> > 
> > Which brings us back to my original question - why is it legal?
> 
> Because within *one* type [Integer in this case] it is a halting problem:
> 
> declare
>    A : Integer := 1;
>    B : Integer;
> begin
>    if HALT (x) then
>       B := 0;
>    else
>       B := 1;
>    end if;
>    A := A / B;
> end;

Sorry, but I think you were confused by my sloppy wording.
The question was not whether divide-by-zero should be illegal
in the general case.  The question was whether X/Y should be
illegal when Y is static, but X is not.

Even in your example above, there's a good argument that the compiler
should (optionally) warn.  That example looks buggy to me!

- Bob