le through the *repl* environment.  One field is 'repl-let which
gives you access to all the repl's internal variables and functions.
Another is 'top-level-let, normally (sublet (rootlet)), which is the environment in
which the repl's evaluation takes place.  You can reset the repl back to its
starting point with: <code>(set! (*repl* 'top-level-let) (sublet (rootlet)))</code>.
You can save the current repl state via <code>((*repl* 'save-repl))</code>, and
restore it later via <code>((*repl* 'restore-repl))<