Building a today-I-learned habit, and displaying the documentation for random Emacs commands

I’d like to build a habit of regularly learning one small thing each day in one of three domains: tech, life, and learning. My measurable output would probably be in the form of index cards, tweets, blog posts, and notes (in org-capture, Dropbox, or Evernote). I can get input from various sources like blog posts, videos, books, webpages, and so on.

2016-02-19a Preparing for a today-I-learned habit -- index card #til #learning

2016-02-19a Preparing for a today-I-learned habit — index card #til #learning

A little bit of randomness might be useful for learning more about Emacs. Emacswiki has a random page function, but the chunks are often a little large or irrelevant. On the other hand, displaying a random command from the packages that I already have loaded into my Emacs – that might be a good way to discover interesting things.

I started by looking at apropos-command, which led me to apropos-internal, which is a C function that referred to obarray. Using obarray by itself didn’t work (suspiciously few elements, so I often ended up looking at emms-related functions). I eventually found mapatoms, which seems to do a better job at listing an appreciable number of interactive functions. I filtered the list to include only documented functions that had not been marked as obsolete: 8,415 in my current Emacs, which should be plenty to go through. =)

(defun my/describe-random-interactive-function ()
  (interactive)
  "Show the documentation for a random interactive function.
Consider only documented, non-obsolete functions."
  (let (result)
    (mapatoms
     (lambda (s)
       (when (and (commandp s) 
                  (documentation s t)
                  (null (get s 'byte-obsolete-info)))
         (setq result (cons s result)))))
    (describe-function (elt result (random (length result))))))

I’ve added this to a key-chord + hydra keymap as a repeatable function, so I can type hh to start my Hydra and then type r as many times as I want in order to show the documentation for a random interactive function. If you’re curious about that, you can see the key-chord section of my config.

Anyway, today I learned more about obarray and mapatoms – they’re not interactive functions, but they were handy for building this little bit of code. We’ll see how it goes! =)