;; count-leaves
;;

(define (count-leaves tree)
  (if (null? tree)
      0
      (if (pair? tree)
          (+ (count-leaves (car tree))
             (count-leaves (cdr tree)))
          1)))

(define tree (list (list 1 2) (list 3 4)))

(define (print-leaves tree)
  (if (null? tree)
      '()
      (if (pair? tree)
          (begin
            (print-leaves (car tree))
            (print-leaves (cdr tree)))
          (begin
            (display tree)
            (newline)))))

;; --- aside : reminder about length of list

(define (length items)   ;;  (1 2 3 4) ...  1 + 1 + 1 + 1 + 0
  (null? items)
  0
  (+ 1 (length (cdr items))))

;; -------------

(display "(count-leaves tree)\n")
(display (count-leaves tree))  ;; prints 4
(newline)

;; ----------------
(display "(print-leaves tree)\n")
(print-leaves tree)

;; -----------------------------

(display "(print-leaves '(1 (list 1 2 3) (list 4 5 6)))) \n")
(print-leaves '(1 (list 1 2 3) (list 4 5 6)))