Install elpa-vala-mode by entering the following commands in the terminal:
sudo apt update sudo apt install elpa-vala-mode
Description:
Emacs editor major mode for vala source code
The package provides a Vala major mode for Emacsen, and sets it up for files with extension vala and vapi.
Homepage: https://wiki.gnome.org/Projects/Vala/Emacs
Version: 0.1-4
Section: universe/editors