5

Is there a (quick) way of resetting a variable to its default value (as defined in some .el file) after it has been modified? e.g. via commands in the .emacs file, without having to restart emacs.

Example: Set ispell-tex-skip-alists to the value as defined in `ispell.el' after modification.

Improve this question
1

3 Answers 3

Reset to default
5

Here you go:

(defun endless/reset-var-at-point ()
  "Revaluate the definition of variable at point."
  (interactive)
  (save-window-excursion
    (save-excursion
      (let ((buf (current-buffer)))
        (find-variable-at-point)
        (when (looking-at-p "(def\\(var\\|custom\\|const\\) ")
          (eval-defun nil))
        (unless (equal buf (current-buffer))
          (bury-buffer (current-buffer)))))))

As others have stated, the initial value of a defvar is not stored anywhere. However, the location of its definition does get stored by Emacs, so you can visit it and reevaluate it.

Note that this will only work if the location of the variable is known, and if it is defined in a conventional way (not as part of a wierd macro or something).
It will also leave a buffer hanging around.

So it is very much not designed for used in lisp code. For interactive use, it should do just fine.

Improve this answer
1
  • ...in which I learn that C-M-x (eval-defun) in a variable (or face) definition actually resets its value (unlike other forms of re-evaluation, which do not).
    – phils
    Apr 20, 2015 at 22:55
4

No. Non-custom variables need not even have a default value.

Except if you mean a global value as opposed to a buffer-local value. In the case of a variable that has buffer-local values, yes, you can use function default-value to obtain its default value, and you can then use setq to set any buffer-local value to that default value. (You can also use set-default-value to change the default value.)

Improve this answer
1

It's possible if the variable was declared as a defcustom:

(eval (car (get 'ediff-split-window-function 'standard-value)))
;; => split-window-vertically

But ispell-tex-skip-alists was declared as defvar, so this isn't possible.

Improve this answer
4
  • 1
    Technically, you can visit the variable definition and reevaluate it entirely with elisp code.
    – Malabarba
    Apr 20, 2015 at 10:55
  • True, but there's no introspection-style option.
    – abo-abo
    Apr 20, 2015 at 11:03
  • The question explicitly asks about a non-custom variable.
    – Drew
    Apr 20, 2015 at 15:03
  • 2
    The question was edited two hours after I provided an answer.
    – abo-abo
    Apr 20, 2015 at 15:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.