Why Having Multiple Emacs Themes if Not Cycling Through Them

June 27, 2024

I don’t think I’m alone in having multiple Emacs themes installed. Am I?

After trying many, I have kept just a few:

acme,
gruvbox,
material,
nano,
nova,
plan9,
solo-jazz,
twilight-bright

There are a few great themes that I like from those coming with Emacs:

adwaita
dichromancy
leuven
modus-operandi
tango
tsdh-light
whiteboard

At this point I reached my dilemma.
With so many themes available, how can I experience them all?

Enter my new Emacs daily theme cycle:

(defun alpo/today-emacs-theme ()
  "Chooses a theme based on the day."
  (interactive)
  (let* ((themes-list (list 'acme 'gruvbox-light-hard 'dichromancy 'material-light 'leuven 'nano-light 'modus-operandi 'nova 'tsdh-light 'plan9 'solo-jazz 'twilight-bright))
         (themes-len (length themes-list))
         (today-as-number (string-to-number (format-time-string "%Y%m%d%j")))
         (theme-index (% today-as-number themes-len))
         (theme-sym (nth theme-index themes-list)))
  (message "Loading theme: %s" theme-sym)
  (load-theme theme-sym)))
(alpo/today-emacs-theme)

An unplanned benefit of the list of chosen themes is that it is not a multiple of 7 and thus the selected theme won’t be the same for the same day of the week.

Here’s what the function is doing:

creates a list of themes to choose from
construct a number based on the date (instead of going for a random I want the same theme for a day)
calculate the theme index based using modulo operation