Re: Disallowing Pre-Defined Operations

[William A Whitaker <whitaker@erols.com>]

No one asks for built-in units checking.  (Actually I did and several
others have talked to me about it, but apparently not to ACT.)  This may
not be unexpected.  ACT talks to the computer people in a company. 
Computer scientists have no brief for units, they deal with bits, and
maybe GUIs.  They get an algorithm and are supposed to implement it. 
That is software.  The managers do not ask for units, thay just want to
job done and expect that the programmeers will take care of it.  The
only way they would know of the problem is when something goes wrong,
like a Mars probe crashes.  And the knowledge is of little use then
because their next managerial job is at McDolalds.

It was not always so.  The first few generations of computers were
designed and built for physicists, who did their own programming.  And
units were important, but physicists were trained to be particularly
careful with them.  Now days the language/compiler could help those who
are not as careful. 

I suggest that a units checking feature would be a valuable selling
feature in Ada, even though one might have to educate the user.  But it
is a step above any individual implementer.  The suggestion that it
would be an interesting experiment as a modification to GNAT is a good
one.  But I hope such work gets widely circulated so that there is
developed a common method of stating the units in a program, however it
is implemented.  And one might advertize that the units pragma in one
system means the same as in another.

Whitaker

Robert Dewar wrote:
> 
> In article <38D2E598.262D1CD5@erols.com>,
>   whitaker@erols.com wrote:
> > Of course, the ideal is an Ada recognition of the Units
> > requirement and implementation at the standard/compiler level.
> 
> I don't see the "of course" here at all. It is not at all clear
> that the damage to the language done by the additional
> complexity here would be worth the additional functionality.
> 
> Given that the discriminants solution works fine, and has an
> efficient implementation, that seems good enough to me. If no
> compiler vendor has bothered to provide this efficient
> implementation, it would tend to indicate that it is simply
> not that important.
> 
> Certainly we have never had any customers asking for such
> a feature, and our customers are not shy when it comes to
> asking for enhancements (the long list of features in the
> new release of GNAT 3.13a is largely fueled by customer
> requests).
> 
> Robert Dewar
> Ada Core Technologies
> 
> P.S. Exploring this more efficient implementation would
> certainly make a nice GNAT-based project for someone to
> undertake.
> 
> Sent via Deja.com http://www.deja.com/
> Before you buy.