The ethics discussion in the neighboring threads aside, this approach has some nasty surprises, and I think it's borderline deceptive that they aren't mentioned

The ethics discussion in the neighboring threads aside, this approach has some nasty surprises, and I think it's borderline deceptive that they aren't mentioned more prominently. It's not that rare that my REPL sessions e.g. in Node are > perform expensive computation ... result ... > transform result ... transformed result ... With this approach, the REPL slows down quadratically with session length, and any expensive command at the beginning is executed over and over again. Also, better don't do any file I/O and then continue the session unless you're prepared for the consequences.