Not Lisp, but for those interested in editing programs that are running in production:
I read some Erlang article saying that hot swapping is not actually very useful in production because of some reasons, and instead a blue-green deployment is preferred. Can't find the link atm. This was close: https://learnyousomeerlang.com/relups
Compare to this comment: https://news.ycombinator.com/item?id=42405168 Hot swaps for small patches and bugfixes, and hard restarts for changing data structures and supervisor tree.
It not that hot swapping isn’t useful, it’s just difficult to do well and you need to write your code in a way that supports it. If you need 0 downtime on a device that can do a blue green deployment then the BEAM has you covered. Most people just don’t need that, so the extra hassle isn’t worth constantly considering how to migrate data in flight.