The Magic Roundabout - A Common Lisp story about a circular list, SBCL and save-lisp-and-die

magic.lisp

;;;; Demonstrate SBCL save-lisp-and-die.

;;; The characters of the Magic Roundabout are on the Magic Roundabout... on
;;; each execution of this program, the roundabout is *rotated* one place and
;;; the name of character at that place is printed.

;;; First load...
;;; sbcl
;;; * (load "magic.lisp")
;;; (magic)
;;; (quit)
;;; thereafter...
;;; ./magic

(defun magic()
  (when (not (boundp 'roundabout))
    (defvar roundabout (list "Dougal" "Zebedee" "Brian" "Ermintrude" "Dylan" "Florence" "Mr Rusty"))
    (setf (cdr (last roundabout)) roundabout))

  (if (not (boundp 'name))
      (defvar name nil))

  (if (eq nil name)
      (setf name (first roundabout))
      (setf name (nth 1 (member name roundabout))))

  (format t "~@a~%" name)

  (sb-ext:save-lisp-and-die "magic" :toplevel #'magic :executable t))