Adding lisp functions to the playlist

[Alex Griffin]

It would be cool if EMMS could include arbitrary lisp functions in the 
playlist, which would be called instead of playing a media track.

Hopefully this idea makes sense to someone other than just me. Obviously, this 
feature isn't strictly necessary to enable lisp code to interact with the EMMS 
playlist, however it would make certain things easier:

1. Functions could be queued after certain tracks. Examples of functions I 
might use this way include:

  - Stopping playback for some length of time
  - Powering off or rebooting my machine
  - Changing the volume
  - Changing the emms player backend

2. You could use standard EMMS key bindings to order and rearrange functions to 
execute, and store them in playlist files.

I'm writing this because I'm not sure how this feature would be implemented or 
if it would need support in upstream EMMS. Although I have written a simple 
emms player backend[1], this idea breaks the media player paradigm a little bit 
so I decided to solicit feedback from the mailing list here.

Is anyone else interested in this? Can it be implemented as a standard player 
backend or would it require upstream support/crazy hacks?

Thanks,
--
Alex Griffin

[1]: https://github.com/ajgrf/emms-player-sonos