;; The exact I/O behavior of this example might vary from implementation
;; to implementation depending on the kind of interactive buffering that
;; occurs.  (The call to SLEEP here is intended to help even out the 
;; differences in implementations which do not do line-at-a-time buffering.)

(defun read-sleepily (&optional (clear-p nil) (zzz 0))
  (list (progn (print '>) (read))
        ;; Note that input typed within the first ZZZ seconds 
        ;; will be discarded.
        (progn (print '>) 
               (if zzz (sleep zzz))
               (print '>>)
               (if clear-p (clear-input))
               (read))))

(read-sleepily)
 |>  > |>>10<<|
 |>  >
 |>  >> |>>20<<|
⇒  (10 20)

(read-sleepily t)
 |>  > |>>10<<|
 |>  >
 |>  >> |>>20<<|
⇒  (10 20)

(read-sleepily t 10)
 |>  > |>>10<<|
 |>  > |>>20<<|  ; Some implementations won't echo typeahead here.
 |>  >> |>>30<<|
⇒  (10 30)