Re: [External] : Re: How to make M-x TAB not work on (interactive) declaration?

[Jean Louis <bugs@gnu.support>]

* Yuri Khan <yuri.v.khan@gmail.com> [2023-01-16 10:57]:
> On Mon, 16 Jan 2023 at 11:44, Jean Louis <bugs@gnu.support> wrote:
> 
> > > >> (+) ➜ 0
> > > >
> > Send me references on what is additive identity.
> >
> > Though that it is so, it does not answer why is it so.
> 
> Consider a sum of n elements: S = (+ x_1 … x_{n-1} x_n).
> By definition, it is equal to the sum of the first n-1 elements, plus
> the nth element: S = (+ x_1 … x_{n-1}) + x_n. No problem this far?
> (except for me mixing prefix and infix notation)
> 
> Now, plug n=1 into this general formula.
> S = x_1 = (+) + x_1.
> Therefore, the sum of an empty list (+) has to be 0.

By above I do not see reference to Lisp. What you state above is not
what Lisp function is supposed to do and it does not tell why is it
so in Lisp, do you know?

I understand "identity element" but I do not see relation between
group theory and arithmetic function in Lisp context `+':

> + is a built-in function in ‘C source code’.
> (+ &rest NUMBERS-OR-MARKERS)
> Return sum of any number of arguments, which are numbers or markers.

It does not say "Return sum of any number of arguments, which are
numbers or markers, or if no arguments return identity element by
using group theory, blah..."

I actually expect function to tell me wrong number of arguments or no
arguments, as I find it safer for programming that way.

-- 
Jean

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