Is there a way to make the left alt key apply a sticky meta modifier?

Question

I'm using vanilla emacs and since I'm using a nonstandard keyboard layout, I've used dual-function-keys to modify the left alt key so it sends left alt if it is tapped and right alt if it is held. I would like emacs to interpret the sent tapped left alt as a command to apply the meta modifier to the next key pressed. The wiki is unclear on whether this is possible [1]. My naive attempts of

  (define-key key-translation-map (kbd "<lmeta>") 'event-apply-alt-modifier)

and

  (define-key key-translation-map (kbd "<lalt>") 'event-apply-alt-modifier)

didn't seem to work. Is there a way to do this?


  [1]: https://www.emacswiki.org/emacs/StickyModifiers

Answer 1

Emacs doesn't process modifiers on their own. It needs a non-modifier key (the key which is being modified) to be involved in order to register a key sequence / binding. So no, I don't believe it's possible to do what you're attempting.

I suppose you could tell your keyboard to make "tapping alt" send a non-modifier event and then tell Emacs to bind that to event-apply-alt-modifier but that's not going to be very helpful for other applications.

To be honest, though, I don't understand what you've done... if you've already configured your keyboard or OS so that tapping alt modifies the next key, why do you need to tell Emacs anything at all? Is it not then receiving the modified key?

(E.g. I use sticky modifier keys, and it's purely an OS-level thing -- Emacs neither knows nor cares that I'm doing that.)