btree_5.rkt

(define t-post-order
  (lambda (t) 
    (if (t-empty? t)
      '() 
      (append (t-post-order (t-left t)) 
              (t-post-order (t-right t)) 
              (list (t-value t)))) ))

(define t-post-order-r
  (lambda (t) 
    (let aux ([t t] [res '()])
      (if (t-empty? t)
        res
        (aux (t-left t)
             (aux (t-right t)
                  (cons (t-value t) res))) ))))

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