I just create new / changed functions next to the others and eval the selected region, then clean up. When I think i'm done, I'll restart the repl and try if it all is fine or if I depended on something in the state. That doesn't often happen anymore. I use the repl to try out things I just written in files. I can't say I remember a moment when state was a/the problem.

M-x slime-restart-inferior-lisp

works fine.