Can I clean the repl?

I have played with a lot of code in a repl console, how can I clear it? I would like a fresh one without restarting it. Can that be done?

If you want to clear the current namespace of all temporary variables and functions you declared you can use this one liner (or make a function of it) :

(map #(ns-unmap *ns* %) (keys (ns-interns *ns*)))

or

(ns myutil)
(defn ns-clean
       "Remove all internal mappings from a given name space or the current one if no parameter given."
   ([] (ns-clean *ns*)) 
   ([ns] (map #(ns-unmap ns %) (keys (ns-interns ns)))))
(ns mytest)

... make loads of junk ...

(myutil/ns-clean)

... great!!! I can now make all new junk ... 

It does not claim to give you a squeaky clean namespace, just one with less of the junk which usually accumulates in a typical repl session.

Use with caution : do not pull the rug from under your feet!

If you are running the repl through a terminal window (eg: Terminal.app on MacOS or xterm/aterm/urxvt etc on linux) then you can type Control-L and it should clear the terminal window and give you a new repl prompt. However all macros/atoms you previously defined are still going to be in memory, so this is just a "Cosmetic" clear.

In EMACS/slime REPLs C-c C-o clears the last output (in case you've typed something that gave a very long answer) C-c M-o clears the whole thing

In GNOME terminals, you've got a menu option Terminal/Reset and Clear