Disable minor mode when keys not in it's keymap are pressed

Question

I was using this to implement line duplication in emacs and decided to bind it to C-c d and it works without problems

What would be cooler though is if I can use C-c d do duplicate a line and then be able to make further duplications of this line by simply typing d. If I want 4 duplications, then the call would be C-c d, d, d, d.

What's the best way to achieve this? I assumed it would be activating a minor mode with C-c d that, when it starts, duplicates a line and then has the duplicate-line function bound to "d" in it's keymap.

The problem with this is that you have to disable the minor mode when a key is pressed that is not in it's keymap. Can this be done?

Or am I approaching this problem completely wrong?

Answer 1

You can use set-transient-map. First, make a sparse keymap with the binding you want for repetition:

(setq duplicate-line-keymap
      (let ((map (make-sparse-keymap)))
        (define-key map (kbd "d") #'my-duplicate-line)
        map))

Then, you can make your function, and at the end, call set-transient-map, and give it the keymap:

(defun my-duplicate-line ()
  (interactive)
  (duplicate-line)
  (set-transient-map duplicate-line-keymap))

Now, when you call #'my-duplicate-line, if you press "d" again, it'll repeat the call to #'my-duplicate-line, but if you press anything else, it'll do that behavior instead. You can put a message in the minibuffer to indicate what's going on:

(defun my-duplicate-line ()
  (interactive)
  (duplicate-line)
  (message "press d to duplicate again!")
  (set-transient-map duplicate-line-keymap))

Answer 2

This is exactly the use case for the hydra package, which you can install via package-install from melpa.

For example:

(defhydra hydra-duplicate-line ()
  "duplicate line"
  ("d" duplicate-line nil))

(global-set-key (kbd "C-c d") 'hydra-duplicate-line/duplicate-line)

This will bind C-c d to a command that will duplicate the current line and leave in a "temporary mode" where pressing d will duplicate the line again, and any other key will exit the hydra and do its usual function.

Hydra can do lots more, but this is a good place to start!