Bear in mind that LispMs had well-designed tools for supporting this kind of development. For example, they had version control that tracked all changes everywhere at all times, even changes that were not saved in any file.
Also bear in mind that they were designed by programmers for programmers. They were not intended for the general public.
> they had version control that tracked all changes everywhere at all times, even changes that were not saved in any file.
No. The file system did auto-versioning, so you could generally recover recent history of a file, but there was nothing that "tracked all changes everywhere".
Well, ZMacs (the editor) did have unbounded 'undo' functionality, and you could even select a function and undo changes to that particular function, even if those weren't the most recent changes to the file. Maybe that's what you have in mind.
It's not something one would probably use every day, or without due care. But it is something you can. And, as I said before, unless you take explicit steps to persist the change across boots, one flick of the big red switch and it's gone.
