That's exactly the kind of misunderstanding parent was talking about :)
Why start somewhere else than your editor, if it's already hooked up to the REPL? When I launch my REPL, I don't think it even accepts stdin, because there is no reason it has to.
It is easy to start creating objects in the repl (say if you are testing an API) and work with those created objects in the repl, one step at a time. You are able to observe the behaviour of the objects every step of the way. This gives you a much better idea when you are writing the functions (usually copy-pasting from repl) in the editor.
I am sure it can be done from the editor itself. (say using the 'comment' block in clojure). It is just matter of preference.