William D Clinger wrote:
>>Would the following proposal satisfy your goals:
>>
>>(a) Mandate unlimited size exact integers in the base language.
>>
>>(b) Push fl+ et al. off into a library module.
>
>
> No.  The fundamental problem with R5RS arithmetic is that
> programmers cannot rely on the behavior of the arithmetic
> primitives.  Mandating exact integers of unlimited size
> would help, but programmers would still not know whether
> (/ 3 4) will evaluate to 3/4, 0, 1, or 0.75.
>
> To solve this problem, we have to require some subset of
> the tower that has reasonable closure properties, while
> banishing any arithmetic operations that are not closed
> over that subset.  We have to do both.

I agree. I would propose that the arithmetic procedures in the base
language be closed over exact integers of unlimited size; that is, I
would banish / and other procedures that are not closed. (Or, maybe,
force them to signal an error, if a suitable error handling mechanism is
defined.) Programmers would then know exactly (sic) the result of all
arithmetic operations in the base language.

Then, I would either mandate the full tower in the library or mandate
SRFI-77 flonum operations in the library. These give the programmer the
full tower, either directly or by using (a modified version of) your
portable code.

I understand this is postulating some means to push the SRFI-77
operations off into a library, but I don't see the problem. I am not
proposing that SRFI-83 implement a general means to import different
languages.

> In my opinion, two fairly extreme positions are the most
> attractive.  Either require the full tower as part of the
> base language, or require only the fixnum/flonum foundation
> while banishing + and the other generic operations to the
> libraries.

I think the major difference between us on this issue is that you think
that modular fixnum arithmetic is adequate for the base language whereas
I do not. I want exact integers of unlimited size because I can see an
argument[*] for making fixnums smaller than the size needed to reference
the largest possible list, string, or vector, and I cannot imagine the
base language not completely defining these operations.

I also like the idea of the arithmetic operations following standard
arithmetic rather than modular arithmetic.

Regards,

Alan

[*] For example, making fixnums 16-bits wide on a 32-bit machine to
allow for quick determination of overflow on multiplication.
--
Dr Alan Watson
Centro de Radioastronomía y Astrofísica
Universidad Astronómico Nacional de México