Right, I expect the version I linked you to doesn't behave exactly like Common Lisp's readline. I just hope it can help. :)
I don't fully understand your example. Did you try something like (do (readline) (readline)), like I was talking about? I'm guessing that since Arc's REPL takes commands and other input from the same stream, it's already different from the REPL you're used to, regardless of how readline works.