Supercollider has a nice emacs mode for working with the supercollider server and editing supercollider code
The mode itself should come with Supercollider, but as others have noted, it’s a bit old.
How to make SuperCollider go "beep" - an introduction to Supercollider using Emacs and
[Supercollider] has an Emacs mode, but unfortunately it has bitrotted. This isn’t surprising – they’ve got a great IDE now. Still, you’ll pry Emacs from my COLD DEAD HANDS.
SuperCollider is packaged with an Emacs mode, but it does not appear to be actively maintained. There is set of extensions available on the MELPA package repo that aim to make the mode feel more modern.
This package includes a number of extensions and improvements: