As in restarting the entire program and re-running every subsequent query/state changing mechanism that got you there in the first place, being careful not to accidentally run other parts of the program, setting it up to be just so, having to then rewrite parts if you then want to try something somewhere else?
Perhaps I'm misunderstanding you, because that sounds horrible unless you're scripting something small with one path.
The whole point of the REPL is that you evaluate whatever functions you need to get into your desired state and work from there. The ad hoc nature of it is what makes you able to just dig into a part of the code base and get going, even if that project is massive.
> Personally, I find waiting more than 200ms unacceptable and really < 50ms is ideal.
Calling a function on a running program takes microseconds; you're not restarting anything.