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

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

On Tue, Oct 26, 2021 at 2:09 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?
>
> This would add it again as the last element:
>
> --8<---------------cut here---------------start------------->8---
> (let ((place (assoc 'company-tabnine th/test)))
>   (setf place (append place '(company-ispell))))
> --8<---------------cut here---------------end--------------->8---

Thanks. But the push doesn't work:

(let ((place (assoc 'company-tabnine th/test)))
  (setf place (push place '(company-ispell))))

Debugger entered--Lisp error: (wrong-number-of-arguments (lambda
(command &optional arg &rest ignored) "`company-mode' completion
backend using Ispell." (interactive (list 'interactive)) (cond ((eql
command 'interactive) (company-begin-backend 'company-ispell)) ((eql
command 'prefix) (if (company-ispell-available) (progn
(company-grab-word)))) ((eql command 'candidates) (let ((words
(company-ispell--lookup-words arg ...)) (completion-ignore-case t))
(if (string= arg "") words (all-completions arg words)))) ((eql
command 'kind) 'text) ((eql command 'sorted) t) ((eql command
'ignore-case) 'keep-prefix))) 0)
  company-ispell()
  (let* ((v (company-ispell))) (\(setf\ quote\) (cons place 'v) v))
  (setq place (let* ((v (company-ispell))) (\(setf\ quote\) (cons place 'v) v)))
  (let ((place (assoc 'company-tabnine th/test))) (setq place (let*
((v (company-ispell))) (\(setf\ quote\) (cons place 'v) v))))
  (progn (let ((place (assoc 'company-tabnine th/test))) (setq place
(let* ((v (company-ispell))) (\(setf\ quote\) (cons place 'v) v)))))
  elisp--eval-last-sexp(nil)
  eval-last-sexp(nil)
  funcall-interactively(eval-last-sexp nil)
  command-execute(eval-last-sexp)

HZ