[M3devel] comparisons vs. subranges

[hendrik at topoi.pooq.com]

On Sat, Mar 13, 2010 at 10:19:21AM +0000, Jay K wrote:
> 
> <*UNUSED*>PROCEDURE CardinalGE0(a:CARDINAL):BOOLEAN=BEGIN RETURN a>=0; END CardinalGE0;
> <*UNUSED*>PROCEDURE CardinalEQN1(a:CARDINAL):BOOLEAN=BEGIN RETURN a=-1; END CardinalEQN1;
> 
> 
>  
> 
> Seems to me, the front end should notice these.
> 
> The first should always be TRUE.
> 
>    And possibly, possibly warn.
> 
> The second should always be FALSE.
> 
>    And possibly, possibly warn.
> 
>  
> 
> "Generic" programming often hits this sort of thing though, a good reason not to warn.
> 
> Programmer might also be working with existing code and have changed INTEGER to CARDINAL.
> 
>   Or be defending against future maintainers changing CARDINAL to INTEGER.

Wasn't there a discussion a while ago about subranges out-of-bounds not 
being a safety problem?  (Or was it arithmetic overflow?)  This 
optimisation might well cause a quite hard-to-find bug if we don't 
guarantee subrange integrity.

-- hendrik