Subject: Re: bug#52290: 28.0.90; Undocumented generalized variables

From: Michael Heerdegen <[email-masked]>
Date: Sun, 05 Dec 2021 17:17:12 +0100

Lars Ingebrigtsen <[email-masked]> writes:

> [...]  I.e., all the generalised variables that are used for side
> effect (as opposed to mutating an explicit object) are liable to cause
> confusion.

I would want to limit this to the kind of side effect: is it undoubtedly
clear what it is, is there a "canonical" side effect?  This is the case
e.g. for `buffer-modified-p' to a high degree, but not for
e.g. `point-max': there are several ways to achieve that `point-max'
will return a certain value - killing a certain amount of text, for
example.  Or narrowing.  Narrowing was not the thing that came to my
mind first.  A setter for it might cause confusion because the semantics
are not clear, in contrast to `buffer-modified-p', I think, where it is
quite clear.

I mean, Emacs is an editor, so we have more aspects of state than
variable bindings.  Setting variables can also have other side effects
than simply changing the variable's binding.  Per se I don't see a
problem in considering more kinds of state (more than variables) as
places.  OTOH, `point-max' for example is not really a self-contained
part of state, it's a value of a computation, a derived value.

The classification result can be a bit subjective and depend on the
viewing point, of course.

Michael.