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

[Tassilo Horn]

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---

Bye,
Tassilo