Re: as for Calc and the math library

[Ihor Radchenko <yantar92@posteo.net>]

Eli Zaretskii <eliz@gnu.org> writes:

>> > If Emacs is to have a math library, the library must use high-quality
>> > mathematical and numerical algorithms that are well-known and
>> > described in many textbooks on this subject matter...
>> 
>> I agree with this point, but I suspect that writing such a library from
>> scratch might be a bit difficult.
>
> It depends on the scope and the person who'd like to work on that.

Yes, of course. If somebody is up to writing a serious math lib, it
would be better. But having a bit simpler task idea can increase the pool
of potential volunteers.

>> May I suggest an alternative: abstract out GNU Calc math routines to be
>> available from Elisp without having to read Calc sources.
>> Such a task would require:
>> 1. Documenting some Calc data structures
>> 2. Possibly refactoring some Calc functions to use simpler API.
>> 
>> It would be a much easier task and can improve the existing
>> functionality.
>
> I don't think I understand well enough what will this entail in
> practice.  Can you show an example of doing this for a couple of
> functions?

For (1), I was referring to ";;;; Arithmetic routines." in
calc.el. Now, people must simply know the internal format of special
number representations to work with Calc from Elisp.
It might be worth (a) putting them into a proper manual (some kind of
Calc Lisp API description); (b) maybe creating constructor functions to
abstract the types away.

For (2), for starters, Calc functions often do not even have
docstrings. One simply has to guess(?) or read the code to understand
what kinds of values can be passed. For example, take `math-add' - no
docstring, and go try adding invalid arguments:

M-: (math-add "foo" '(frac 1 2))

Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p "foo")
  (math-mul "foo" 2)
  (calc-add-fractions "foo" (frac 1 2))
  (math-add "foo" (frac 1 2))

The error checking could be improved, especially since it is a
polymorphic function that is capable of doing things like

(math-add '(vec (frac 1 2) 3 1) '(frac 1 2)) ; => (vec 1 (frac 7 2) (frac 3 2))

but somehow not

M-: (math-add 0.1 '(frac 1 10))

Debugger entered--Lisp error: (wrong-type-argument integer-or-marker-p 2.0)
  (math-gcd 2.0 10)
  (math-make-frac 2.0 10)
  (calc-add-fractions 0.1 (frac 1 10))
  (math-add 0.1 (frac 1 10))

> In any case, this job, as any other job in Emacs, needs its
> volunteer(s).  Until we have such volunteers, it's all academic.

Yes, of course. I was hoping that Emanual (who is apparently interested
in this topic, or at least in improving Elisp) can be the one.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>