I’ve realised how many languages have their own editor.
vi was written in C for coding on Unix, mostly in C. emacs was written in Lisp, for writing Lisp. I used an editor called TPU (Text Processing Utility) that could be customised and extended in Pascal, in a very similar way to emacs. Sublime is extendable in Python and Atom is written using web-technologies.
Are there others? Having a different editor for every language doesn’t seem any more desirable than having a different IDE on each OS to me. [waves to Visual Studio]