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


From: Hongyi Zhao
Subject: Re: Add/remove an element into/from a cons.
Date: Tue, 26 Oct 2021 14:07:08 +0800

On Tue, Oct 26, 2021 at 1:42 PM Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
>
> On Tue, Oct 26, 2021 at 1:40 PM Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
> >
> > On Tue, Oct 26, 2021 at 12:58 PM Tassilo Horn <tsdh@gnu.org> wrote:
> > >
> > > Hongyi Zhao <hongyi.zhao@gmail.com> writes:
> > >
> > > > How can I add/remove an element into/from a cons, taking the following
> > > > one as an example:
> > > >
> > > > ```emacs-lisp
> > > > (setq company-backends '((company-tabnine :separate company-capf
> > > > company-dabbrev company-keywords company-files company-ispell)))
> > > > ```
> > > >
> > > > How can I  remove `company-ispell` from and re-add it into the
> > > > company-backends defined above?
> > >
> > > You can use `setf' with the place being the alist entry like this
> > > (company-backends replaced with th/test in my example):
> > >
> > > --8<---------------cut here---------------start------------->8---
> > > (setq th/test '(( company-tabnine :separate company-capf company-dabbrev
> > >                   company-keywords company-files company-ispell)))
> > >
> > > (let ((place (assoc 'company-tabnine th/test)))
> > >   (setf place (remove 'company-ispell place)))
> > > --8<---------------cut here---------------end--------------->8---
> >
> > Yes. It does the trick:
> >
> > `C-j' (setq th/test '((company-tabnine :separate company-capf 
> > company-dabbrev
> >                  company-keywords company-ispell company-files)))
> >
> > ;; ((company-tabnine :separate company-capf company-dabbrev
> > company-keywords company-ispell company-files))
> >
> >
> > `C-j' (setq th/test (let ((place (assoc 'company-tabnine th/test)))
> >         (setf place (remove 'company-ispell place))))
> >
> > ;; (company-tabnine :separate company-capf company-dabbrev
> > company-keywords company-files)
> >
> > But how to add it back to the alist?
>
> I mean: But how to add it back to its original position in the list?

BTW, I want to use the above trick to simplify the following function
but failed:

(setq company-backends '((company-tabnine :separate company-dabbrev
company-keywords company-files company-ispell company-capf)))

(defun my-scratch-init ()
  (with-current-buffer "*scratch*"
    (setq-local company-backends
        '((company-tabnine :separate company-capf company-dabbrev
company-keywords company-files)))
    ))

==>

(defun my-scratch-init ()
  (with-current-buffer "*scratch*"
    (setq-local company-backends (let ((place (assoc 'company-tabnine
company-backends)))
                   (setf place (remove 'company-ispell place))))
    ))

HZ



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