Re: Disallowing Pre-Defined Operations

[mark_biggar@my-deja.com]

In article <8aqc0e$n851@ftp.kvaerner.com>,
"Tarjei T. Jensen" <tarjei.jensen@kvaerner.com> wrote:
>
> Tucker Taft wrote in
> >I understand your goal, and it is reasonable. The usual question is
> >whether it is worth the cost. There are so many great ideas that
> >are possible, but only so many can be accommodated in a single
> >language. What you really want are a small number of very powerful
> >and flexible concepts that allow you to solve all the
> >interesting problems elegantly and safely. Personally, I would like a
full-up
> >"units" capability, where generally A * A => A is not defined, since
> >that doesn't balance from a units point of view. I have some ideas
> >how to get there, and would be interested in opinions from others.
> >The techniques using discriminants are unsatisfactory in my view,
> >and too "heavy." VHDL has the notion of "units" built into the
language,
> >and its approach should probably be evaluated.
>
> I think a "units" facility will be very attractive. I would think that
it
> woulld make Ada more attractive to the people who would ordinarily use
Fortran.
> I also think that it might be useful for those who create safety or
life
> critical software.
>
> I think it is long overdue to be able to add oranges and apples and
get fruit
> as the result.
>
> Whether this is achived by adding keywords or pragmas, I don't care.


I have always thought that a simple pragma to turn on some compiler
support for the Discriminate record Units implementation, so that
the compiler automatically generated the code for the necessary
discriminate comparisions on "=", "<", "+", "-", etc. and also
generated necessary discriminate recomputation on "*" and "/".
This would allow the compiler to optimize the static cases.  The
user would only have to define the math part fo each operation, the
compiler would generate every thing else.

--
Mark Biggar
mark@biggar.org


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