Emacs: how to bind a key tapped twice?

I am 开发者_如何学Gousing Emacs (23) and I am binding the C-. key combination to a function:

(global-set-key (kbd "C-.") 'myfunction)

Is it possible to bind a quick "double tap" of a key? For example, I would like to call a function myfunction when typing . quickly two times.

There isn't anything built in, but you can use this code. Customize the variables dc-single-click-cmd and dc-double-click-cmd to be the commands you want.

Note: this introduces a slight delay, b/c the code needs to wait for a little bit of time to determine whether the event was a single or double click.

(defvar dc-single-click-cmd 'dc-example-single-click)
(defvar dc-double-click-cmd 'dc-example-double-click)
(defvar dc-click-timer nil
  "Pending single-click event.")
(defun dc-example-single-click ()
  (interactive)
  (message "A single click just happened."))
(defun dc-example-double-click ()
  (interactive)
  (message "Wait!  I meant double click."))
(defun dc-click-cmd ()
  "Either kick off a single click, or a double click."
  (interactive)
  (if dc-click-timer
      (progn
        (cancel-timer dc-click-timer)
        (setq dc-click-timer nil)
        (call-interactively dc-double-click-cmd))
    (setq dc-click-timer (run-at-time (when double-click-time 
                                            (/ 1000.0 double-click-time))
                                      nil
                                      'dc-call-single-click))))
(defun dc-call-single-click ()
  "spawn the single click"
  (setq dc-click-timer nil)
  (call-interactively dc-single-click-cmd))

I believe KeyChord is the canonical solution to this nowadays.

(Disclaimer: I don't use KeyChord myself (yet), but many people do, so I am certain it is at least worth trying.)

(defun myfunction2 () (interactive) (if (not (eq last-command 'myfunction2)) (insert ".") (setq this-command nil) (delete-backward-char 1) (call-interactively 'myfunction)))

(defun myfunction () (interactive) (message "MYFUNCTION"))

(global-set-key "." 'myfunction2)

https://github.com/k-talo/double-type.el offers similar functionality to what you are looking for.