;; A test input:
(setf input "01 234 567 89")

;; the recursive function
(defun number-to-tone (num-stream &aux low-high dur)
  (setf current (pop num-stream))
  (unless current (return-from number-to-tone s))
  (setf dur (if (equal current #\>) 0.1 0.068))
  (setf low-high
        (case current
              (#\> '(1100 1700)); KP
              (#\< '(1500 1700)); ST
              (#\1 '(700 900))
              (#\2 '(700 1100))
              (#\3 '(900 1100))
              (#\4 '(700 1300))
              (#\5 '(900 1300))
              (#\6 '(1100 1300))
              (#\7 '(700 1500))
              (#\8 '(900 1500))
              (#\9 '(1100 1500))
              (#\0 '(1300 1500))
              (t nil)))
  (seq (number-to-tone num-stream)
       (if low-high
           (sim (osc (hz-to-step (first low-high)) dur)
                (osc (hz-to-step (second low-high)) dur)
                (s-rest 0.136))
           (s-rest 0))))

;;; Start of the main program
(setf *sr* *sound-srate*)
; initialize s to 0 length
(setf s (s-rest 0))

; String to chars
(setf numbers
      (cons #\<  ; append st
            (reverse (cons #\>  ; append kp
                     (get-output-stream-list
                        (make-string-input-stream input))))))

; Return sound
(abs-env (mult 0.4 (number-to-tone numbers)))