Re: Language Revision : "/" and "div"

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Fri, 30 Apr 2010 23:52:18 -0700 (PDT), vincent.diemunsch@gmail.com
wrote:

> I wonder why Ada uses "/" to express the integer division and not
> "div".

Because in most languages / denotes "integer division", which mathematical
integer lack (:-)).

> This leads to the fact that an expression like 4/3*6 that any decent calculator
> would evaluate as 8 is in Ada evaluated as 6 !!! That is a shame :-).

1. The calculator uses reals, not integers.
2. There exist expression which cannot be evaluated (as decimal fractions
of finite length), e.g. 1.0/3.0
3. There exist operations not closed in R. So a "decent" calculator should
return j for sqrt(-1.0) 
4. There exist operations not closed in C, e.g. multi-valued functions. A
"decent" calculator must return a set of values?

> - discard the function "/" (left, right : Integer) return Integer and
> replace it by the operator "div",

AFAIK, ARG does not introduce backward incompatibilities unless absolutely
necessary (in their opinion (:-)). I doubt that / could fall under this
category.

> that sounds quite logical with the existing "rem" and "mod".
> - add a fraction package with a function "/" (left, right :
> Integer'base) return Fraction; as constructor.

Arguably better would be "div" as a full division, e.g. returning a tuple
of the result and the remainder. In both cases there is a problem that the
result type (be it fraction, tuple, rational etc) shall be defined
(inferred) for each integer type including user-defined ones. Ada lacks any
mechanics for this.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de