Emacs tip-of-the-day

gistfile1.el

(defun totd ()
  (interactive)
  (with-output-to-temp-buffer "*Tip of the day*"
    (let* ((commands (loop for s being the symbols
                           when (commandp s) collect s))
           (command (nth (random (length commands)) commands)))
      (princ
       (concat "Your tip for the day is:\n"
               "========================\n\n"
               (describe-function command)
               "\n\nInvoke with:\n\n"
               (with-temp-buffer
                 (where-is command t)
                 (buffer-string)))))))

I changed loop to cl-loop in Emacs 26.1 to make this work.