Mode-local variables in Emacs

Question

I would like to have a global keyboard shortcut that shows the value of a variable. However, the variable's value could change according to the current major mode in the current buffer.

I tried to add the following to my ~/.emacs:

(defun my-elisp-mode-setup ()
  (defvar-local *current-mode-var* "elisp-mode")
)
(defun my-sh-mode-setup ()
  (defvar-local *current-mode-var* "sh-mode")
)
(add-hook 'emacs-lisp-mode-hook 'my-elisp-mode-setup)
(add-hook 'sh-mode-hook 'my-sh-mode-setup)

If I now start Emacs with emacs test.sh and then type M-x describe-variable *current-mode-var* in the test.sh buffer, I get

*current-mode-var*'s value is "elisp-mode"

  Automatically becomes buffer-local when set.

Documentation:
Not documented as a variable.

while I expected to get *current-mode-var*'s value is "sh-mode"

abo-abo · Accepted Answer · 2014-01-05 19:17:48Z

4

The variables are evaled only at first declaration. All further declarations are skipped. You need a setq instead.

answered Jan 5, 2014 at 19:17

abo-abo

20.5k3 gold badges55 silver badges75 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Håkon Hægland Over a year ago

Thanks! If I use setq how can then the variable become local?

abo-abo Over a year ago

It's buffer local after the declaration. This is something like declaring the type and assigning in C: assignment doesn't change type. So defvar-local followed by setq will not change the variable to non-local.

Håkon Hægland Over a year ago

Ok.. Does this mean that you have to add a (defvar-local *current-mode-var* nil) in the ~/.emacs and then use setq in the mode hooks?

abo-abo Over a year ago

Yes, that should work. Or declare in each mode, and setq in each mode. Doesn't hurt to declare stuff.

Tobias Over a year ago

In emacs 24 you can use setq-local.

displayname · Accepted Answer · 2016-08-20 14:29:36Z

3

I prefer official native package https://www.emacswiki.org/emacs/ModeLocal . It is better configurable, because you do not require add-hook

For example

(require 'mode-local)
(setq-mode-local sh-mode *current-mode-var* "sh-mode")
(setq-mode-local emacs-lisp-mode *current-mode-var* "elisp-mode")

Then by just changing mode cause changing the value of *current-mode-var*

answered Aug 20, 2016 at 14:29

displayname

8689 silver badges10 bronze badges

Comments

Drew · Accepted Answer · 2014-01-05 22:35:25Z

2

If all you want to do is examine a variable to determine the major mode (which it seems is what you are doing), then just examine variable major-mode. That's what it's for.

And if you want a key/command to do that, then just create one:

(defun which-mode ()
  "Echo the current major mode in the echo area."
  (interactive)
  (message "Major mode: %s" major-mode))

Or use variable mode-name if you prefer a human-friendly major-mode name.

answered Jan 5, 2014 at 22:35

Drew

30.9k7 gold badges81 silver badges111 bronze badges

Comments

nichijou · Accepted Answer · 2021-01-15 07:06:00Z

1

defvar-local is a macro calling defvar and make-variable-buffer-local under the hood.

defvar SYMBOL [VALUE [DOC-STRING]

... But if SYMBOL is not void, VALUE is not evaluated, and SYMBOL’s value is left unchanged...

You code should be:

(defvar-local *current-mode-var*)

(defun my-elisp-mode-setup ()
  (setq *current-mode-var* "elisp-mode"))
(add-hook 'emacs-lisp-mode-hook 'my-elisp-mode-setup)

(defun my-sh-mode-setup ()
  (setq *current-mode-var* "sh-mode"))
(add-hook 'sh-mode-hook 'my-sh-mode-setup)

answered Jan 15, 2021 at 7:06

nichijou

5145 silver badges13 bronze badges

Collectives™ on Stack Overflow

Mode-local variables in Emacs

4 Answers 4

5 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

5 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related