I've been live-coding my Lua-based markup language luaML using a driver program. Now I've pulled luaML into the driver program so that I can open multiple buffers, move them around, zoom in, zoom out, etc.
(And yes, you can live-program the driver. Not quite using itself, but by copying it into a "meta driver" and making a handful of edits.)
Compare v1 of the driver: https://merveilles.town/@akkartik/109182295383555872; v2: https://merveilles.town/@akkartik/109420170803345855