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

[Hongyi Zhao]

On Wed, Oct 27, 2021 at 9:39 AM Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
>
> 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)

I also tried the following snippet, but still failed:

(defun hz/company-tabnine-remove-company-ispell ()
    (make-local-variable 'company-backends)
    (cond
     (
      (derived-mode-p 'emacs-lisp-mode)
      (setf (alist-get 'company-tabnine company-backends)
            (remove 'company-ispell (alist-get 'company-tabnine
company-backends))))
     (
      t
      (setf (alist-get 'company-tabnine company-backends)
        (append (alist-get 'company-tabnine company-backends)
            '(company-ispell))))))

(add-hook 'emacs-startup-hook #'hz/company-tabnine-remove-company-ispell)

HZ