I had a comment on another video asking how to recompile functions as a program is running. This is the answer.
The code follows:
(defun update-swank ()
"Called from within the main loop, this keep the lisp repl
working while cepl runs"
(continuable (let ((connection (or swank::*emacs-connection* (swank::default-connection)))) (when connection
(swank::handle-requests connection t)))))
(defmacro continuable (&body body)
"Helper macro that we can use to allow us to continue from an
error. Remember to hit C in slime or pick the restart so errors don't kill the app."
`(restart-case (progn ,@body) (continue () :report "Continue")))