;;
;; This emacs program draws some flies buzzing around on the screen.
;;
(with-current-buffer (get-buffer-create "*flies*")
  (switch-to-buffer "*flies*")
  (erase-buffer)
  (setq cursor-type nil)
  (ruler-mode)
  (let* ((cols nil)
         (flies-n 20)
         (howlong 100)
         (spread 70)
         (delay 0.1)
         (sprites (list "O|O" ":/:" "olo")))
    (delete-region (point) (point-max))
    (dotimes (i flies-n)
      (push (list :col (random spread)
                  :state (random (length sprites))) cols))
    (dotimes (i howlong)
      (dolist (b cols)
        (let ((col (plist-get b :col))
              (state (plist-get b :state)))
          (move-beginning-of-line 1)
          (delete-region (point) (line-end-position))
          (setq col (min spread (max 0 (+ col (- (random 3) 1)))))
          (insert (make-string col 32))
          (plist-put b :col col)
          (insert (elt sprites state))
          (plist-put b :state (% (+ state 1) 3))
          (newline)))
      (sit-for delay)
      (erase-buffer)))
  (discard-input)
  (kill-buffer (current-buffer)))