(load "chez-init.ss")


;;; from EOPL2, page 46

(define-datatype bintree bintree?
  [leaf-node (datum number?)]
  [interior-node
   (key symbol?)
   (left-tree bintree?)
   (right-tree bintree?)])

;;; from EOPL2, page 46

(define leaf-sum
  (lambda (t)
    (cases bintree t
	   [leaf-node (x) x]
	   [interior-node (key left right)
			  (+ (leaf-sum left) (leaf-sum right))])))


;;; Let's create some sample data:

(define t1 (leaf-node 3))
(define t2 (leaf-node 4))
(define t3 (interior-node 'a t1 t2))
(define t4 (interior-node 'b t3 (leaf-node 4)))