Re: Add/remove an element into/from a cons.

[Hongyi Zhao <hongyi.zhao@gmail.com>]

On Wed, Oct 27, 2021 at 3:19 AM Tassilo Horn <tsdh@gnu.org> wrote:
>
> Hongyi Zhao <hongyi.zhao@gmail.com> writes:
>
> >> You mean, the above function changes the value not only in *scratch*
> >> but all buffers?
> >
> > After using the above function, it disables me to check the value of
> > `company-backends' when I switch from scratch to other buffers.
>
> What?
>
> > The following message will be triggered when I call `C-h v
> > company-backends RET':
> >
> > Type "q" to restore previous buffer, SPC to scroll help.
>
> Yes, but how does that message hinder you from checking the value of
> `company-backends'?

I can't reproduce this now.

> > I'm using company-tabnine package and the following company-backends
> > setting:
> >
> > (setq company-backends '((company-tabnine :separate company-dabbrev
> > company-keywords company-files company-ispell company-capf)))
> >
> > I want to disable the company-ispell backend when I'm in
> > emacs-lisp-mode. The following function will do the trick:
> >
> >   (defun hz/scratch-init ()
> >     (with-current-buffer "*scratch*"
> >        (setq-local company-backends
> >                  '((company-tabnine :separate company-capf
> > company-dabbrev company-keywords company-files)))
> >   ))
> >
> > (add-hook 'emacs-lisp-mode-hook #'hz/scratch-init)
>
> Well, your function will always run when `emacs-lisp-mode' or a mode
> derived from it, like `lisp-interaction-mode', the major-mode of
> *scratch*, is activated.  But it evaluates that code always in *scratch*
> which defeats the purpose of disabling company-ispell in every buffer
> having `emacs-lisp-mode' as major-mode.
>
> > But as I've posted here, considering that I've also had a definite
> > company-backends setting, so I want to remove the company-ispell from
> > it programmatically.
> >
> > I hope this time I've clearly stated my intention.
>
> I guess so.  In certain modes, you would like to have `company-ispell'
> removed from the company-tabnine entry of company-backends.  Right?
>
> In that respect, I think a function like
>
> --8<---------------cut here---------------start------------->8---
> (defun hz/company-tabnine-remove-company-ispell ()
>   (make-local-variable 'company-backends)
>   (setf (alist-get 'company-tabnine company-backends)
>         (remove 'company-ispell
>                 (alist-get 'company-tabnine company-backends))))
> --8<---------------cut here---------------end--------------->8---
>
> should do the trick.  However, I can imagine that you might not be able
> to use it in major-mode hooks such as `emacs-lisp-mode' due to ordering
> issues, i.e., I can easily imagine that `company-mode' (and this
> company-tabnine thingy) is initialized *after* the major-mode hook has
> run because usually, you activate minor-modes in major-mode hooks.  In
> that case you would try to remove before the company-tabnine entry has
> been added to company-backends.
>
> That's all just guesswork since I don't use company.

I have changed the original function to the following form:

```emacs-lisp
(defun hz/company-tabnine-remove-company-ispell ()
    (setq-local company-backends
        '((company-tabnine :separate company-capf company-dabbrev
company-keywords company-files))))
```

Based on my tries, your above suggest code will set and append the
following value to the current buffer's company-backends:

(company-tabnine :separate company-capf company-dabbrev
company-keywords company-files)

HZ