btree_4.rkt

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

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

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