Emac: Quick Hacks

Published on Jul 01, 2018

Intro

I spend most of my time inside Emacs ― the truly extensible environment. I keep adding new functions/commands to my Emacs configuration that help me accomplish just about anything I would like to. In this post, I am sharing with you two such functions.

Code

(defun do-when-idle (f g interval)
  "Call F when idle for INTERVAL seconds and then G when there is activity.
Thanks to Michael Heerdegen <michael_heerdegen@web.de>."
  (letrec ((run-timer-fun (lambda ()
                            (run-with-idle-timer interval
                                                 nil
                                                 (lambda ()
                                                   (funcall f)
                                                   (add-hook 'post-command-hook
                                                             activity-fun)))))
           (activity-fun (lambda ()
                           (remove-hook 'post-command-hook activity-fun)
                           (funcall g)
                           (funcall run-timer-fun))))
    (funcall run-timer-fun)))

I use the above function for things like 

(do-when-idle #'coin-ticker-mode
              (lambda ()
                (coin-ticker-mode -1))
              60)

(defvar limit-usage (make-hash-table :test 'equal))
(defun limit-usage (command max-minutes)
  "Limit usage of COMMAND to only once in MAX-MINUTES."
  (advice-add command
              :around
              `(lambda (orig-fn &rest args)
                 (let* ((hash-key ,(symbol-name command))
                        (last-ts (gethash hash-key limit-usage))
                        (gap-in-minutes (and last-ts
                                             (/ (time-to-seconds
                                                 (time-subtract (current-time)
                                                                last-ts))
                                                60))))
                   (if (and gap-in-minutes (< gap-in-minutes ,max-minutes))
                       (message "Last Accessed: %s Time to go: %.2f minutes"
                                (format-time-string "%FT%T%z" last-ts)
                                (- ,max-minutes gap-in-minutes))
                     (apply orig-fn args)
                     (puthash hash-key (current-time) limit-usage))))))

I use the above function for limiting how frequently I check email: 

;; Check mail not more than once every 4 hour.
(limit-usage #'gnus (* 4 60))

Conclusion

Emacs is configurable in almost every aspect. Besides the advantages, the only problem with it is that it encourages dislike for the defaults. This costs me some time every week if not everyday. Being customizable to the core, it demands a lot of time to be spent on it before it becomes useable.