bug#54074: 29.0.50; Feature request emacs keymap-set and minor-modes

[Lars Ingebrigtsen <larsi@gnus.org>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> I'm not sure I understand the use case.  Isn't the way to do this just
>> to have my-mode add itself to isearch-mode-hook, and then have my-mode
>> have a minor mode keymap with the prefix it uses?
>
> I think the use case is basically any minor mode which currently uses
> `define-key` in its body to modify some other package's keymap.

But why do that instead of using a minor mode?  I think many cases where
packages do this, it's because the idea didn't really occur to the
people that did the implementation.

> I think we should provide an API to do that meaningfully.  I.e. instead
> of having a minor mode just bluntly set a variable, associate with each
> global var a pair (VAL . FUNS) of a base value and a list of functions,
> where the effective value (the one that should be stored in the
> `symbol-value`, barring intervention from code that disregards the new
> API) is (FUN1 (FUN2 (... VAL))).

As Eli noted, isn't this kinda `add-variable-watcher'?  But:

> The minor mode can then add/remove a function from the list, and just as
> is the case with `add-hook`, `add-function`, etc... it will correctly
> handle the case where the additions/removals are not nested.

My feeling is that this would be both too complicated for most people
writing modes, and it would be really confusing for us people that have
to try to figure out what's actually going on, and finally, values in
Emacs Lisp are mutable, so it won't work reliably anyway.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no