Who in his right mind would use an editor that cannot even do symbolic integration?

Joking aside, I suspect that this is mostly due to two factors:

1. Emacs was used by a lot of smart people, and one of them, David Gillespie got carried away a bit.

2. Thirty years ago, when David Gillespie first started working on calc, emacs lisp (despite at the time lacking even floating points numbers IIRC!), was probably one of the most expressive fairly widely deployed languages around, particularly for the type of symbolic manipulation you need to do for computer algebra. And unlike other things that were used by smart people 30 years ago, emacs still sticks around, so survivorship bias also plays a role.

It's a bit like asking why Windows has a calculator :).

Emacs is best viewed a Lisp execution platform with a built-in text UI. Much like it has a "c++ app", "terminal app" and "compile this" app, it also ships with a "calc app" (literally called "calc"). Since it was being used by lot of mathy people for lot of mathy stuff, it ended up being a proper scientific calculator application.

(Also, Lisps are inherently friendly for doing any kind of symbolic calculations. A Lisp system is one of the least surprising places to find a symbolic integrator in.)

Emacs is best understood not just as an editor, but as an integrated computing environment promoting user freedoms to the fullest extent possible in a manner naturally integrated with its user interface and extensibility. In that sense, it shouldn’t be the least bit surprising to see the kind of in-built application suite one would expect from an operating system or desktop environment. One must also remember that historically the most common computer (power) users were academics, and not “software developers” — so expect a lot of scratches for their itches.

It’s a bit like asking why does bash come with a utility like awk or bc; it’s equally natural.

Have you tried asking your local psychotherapist?

    M-x doctor RET

    I am the psychotherapist.  Please, describe your problems.  Each time
    you are finished talking, type RET twice.

    Why does Emacs need Symbolic Integration?

    What do you think?

    I don't know, just answer the question!

    Why do you say you do not know just answer the question?

    [...]

Maybe you'll have better luck than I did with mine.

The manual actually answers this very question: https://www.gnu.org/software/emacs/manual/html_node/calc/His...

In general - developers use calculators all the time (most frequently via Google these days, but also via REPLs) so a dedicated calculator is a self-evidently useful widget for any editor. It’s is not essential fir a new editor in 2021 but considering emacs has had Calc for some time, it is worthwhile to make improvements to widely-used legacy software. Many emacs users have used Calc in lieu of alternative “developer calculators” like Octave, the R REPL, etc, so it’s not like Calc is an extraneous feature.

It’s uncommon for developers to deal with integral equations in their day-to-day work. But it’s obviously not unheard of - integral equations show up naturally in many domains of finance and engineering. I’ve had to deal with numeric integration on .NET in one of my jobs. Sometimes an exact symbolic solution is easier for the developer and the CPU than a numeric technique, so for a small handful of developers a symbolic integral calculator is a handy (if somewhat specialized) tool, and not just some bell-and-whistle.

> But why does emacs have that functionality?

GNU Emacs is a 36 year old tool that's been targeted at programmers its entire life, is built on an interactive Lisp environment, and actively encourages external improvements and contributions. The more interesting question is why _wouldn't_ it have that functionality.

Because it can... don't underestimate the amount of unrelated things you can crame into a 40 year old software.

Interestingly, nowadays it's really difficult to convince people to add new features, like enabling mouse scrolling by default [1].

[1] https://lwn.net/ml/emacs-devel/20200906133719.cu6yaldvenxubc...

I often find it useful t do a calculation while I am editing. For example when I write a invoice I have to calculate taxes.

I have not had to use the more advanced features. I did not know that they were there. Now I know, perhaps I do need them?

Emacs is a big Lisp interpreter.

Elisp is the most popular Lisp in the world.

Why wouldn’t you want to improve it?

Because enough of its users use it?

I'm a graphics programmer and I use Emacs' in-built RPN calc for its linear algebra capabilities almost daily.

A healthier approach is to have a separate non-Emacs app that can do symbolic integration, which can be run seamlessly from within Emacs.

Otherwise, with all its extensions Emacs starts giving the impression of an Apple-like walled garden, which is not a good comparison for a free software, no?