Re: inverse of add-to-list: remove-from-list

[Boruch Baum <boruch_baum@gmx.com>]

> On Okt 13 2020, Uwe Brauer wrote:
> > But there is, as far as I know, no inverse functionality

1] Similar to what Andreas suggested, try this:

     (let ((aa '(1 2 3 1 4 1 2)))
       (delete 2 aa)
       aa)

   And note that the fine distinction made in the docstring for the
   `delete' function:

     "If SEQ is not a list, deletion is never performed destructively;
      instead this function creates and returns a new vector or string.

      Write ‘(setq foo (delete element foo))’ to be sure of correctly
      changing the value of a sequence ‘foo’.

   So, in the case of SEQ being a list, there is no need to `setq foo'.

2] That really could/should be made clearer in the docstring; something
   like:

  "If SEQ is a list, the original symbol is modified in place, ie.
   destructively. If SEQ is not a list, eg. a vector or string, this
   function creates and returns a new vector or string, and you must
   explicitly ‘(setq foo (delete element foo))’ to alter the original."

  If there's agreement on this docstring change, can it be committed?

3] Emacs also offers a more flexible function `cl-delete'. See there.

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