(defun greet-user (user-name)
  (format t "~%Ave, O ~A !~2%" user-name))

(defun ask (prompt type)
  (loop
    :for input :=  (progn
                     (format *query-io* "~%~A " prompt)
                     (finish-output *query-io*)
                     (if (subtypep type 'string)
                         (read-line *query-io*)
                         (read *query-io*)))
    :until (typep input type)
    :do (format *error-output* "~&Input ~S is not of expected type ~S ; try again.~%" input type)
    :finally (return input)))

(defun ask-user-name ()
  (ask "What is your name? " 'string))

(defun ask-number ()
  (ask "Please give a small integer: " '(integer 0 999)))

(defun decimal-representation-length (n)
  "Return the number of decimal digit used in the usual decimal representation of the non-negative integer N."
  (check-type n (integer 0))
  (if (zerop n)
      1
      (ceiling (log (1+ n) 10))))

(defun connect (a b)
  (let ((s (decimal-representation-length b)))
    (+ (* a (expt 10 s)) b)))

(defun reverse-number (n)
  (loop :repeat (decimal-representation-length)
        :for c := n :then (truncate c 10)
        :for r := (mod c 10) :then (+ (* r 10) (mod c 10))
        :finally (return r)))

(defun program ()
  (greet-user (ask-user-name))
  (let ((n (connect (ask-number) (ask-number))))
    (* n (reverse-number n))))