;;; display of tree nodes
;;; that look like (bintree value left right)

(define spacebox (make-string-box " " ))

(define (make-bintree-box e)
  ;; make a box for e = (bintree val x y)
  (let* ((val (form-box (cadr e)))
	 (subtrees
	  (make-hbox spacebox (map form-box (cddr e)) emptybox emptybox)))
    (make-box  (box-width subtrees)
	      (box-height val) ; new centerline
	      (append (pad-lines-ctr (- (box-width subtrees) (box-width val))
				     (box-lines val))
		      (box-lines subtrees)))))
    
(put 'bintree 'box-formatter make-bintree-box)


;;; bst.scm -- Binary Search Trees (A & S section 2.2.5) modified to have
;;; header "bintree"
;;;

(define (entry tree) (cadr tree))
(define (left-branch tree) (caddr tree))
(define (right-branch tree) (cadddr tree))
(define (make-tree entry left right)
    (list 'bintree entry left right))

(define tree1
    (make-tree 7
	(make-tree 3
	    (make-tree 1 '() '())
	    (make-tree 5 '() '()))
	(make-tree 9 '() (make-tree 11 '() '()))))

(define (element-of-set? x set)
    (cond
	((null? set) #f)
	((= x (entry set)) #t)
	((< x (entry set))
	    (element-of-set? x (left-branch set)))
	((> x (entry set))
	    (element-of-set? x (right-branch set)))))