btree_6.rkt

(define t-size
  (lambda (t) 
    (if (t-empty? t)
      0   
      (+ 1
         (t-size (t-left t))
         (t-size (t-right t)))) ))

(define t-size-r
  (lambda (t)
    (let aux ([t t] [res 0])
      (if (t-empty? t)
        res
        (aux (t-right t) (aux (t-left t) (+ res 1))))) ))

(printf "size       : ~s~n" (t-size my-tree))
(printf "size       : ~s~n" (t-size-r my-tree))