exercise2-63.lisp

(define (entry tree) (car tree))
(define (left-branch tree) (cadr tree))
(define (right-branch tree) (caddr tree))
(define (make-tree entry left right)
  (list entry left right))

(define (tree->list-1 tree)
  (if (null? tree)
    '()
    (append (tree->list-1 (left-branch tree))
            (cons (entry tree)
                  (tree->list-1 (right-branch tree))))))

(define (tree->list-2 tree)
  (define (copy-to-list tree result-list)
    (if (null? tree)
      result-list
      (copy-to-list (left-branch tree)
                    (cons (entry tree)
                          (copy-to-list (right-branch tree)
                                        result-list)))))
  (copy-to-list tree '()))

(define fig2-16-1 '(7 (3 (1 () ()) (5 () ())) (9 () (11 () ())))) 
(define fig2-16-2 '(3 (1 () ()) (7 (5 () ()) (9 () (11 () ()))))) 
(define fig2-16-3 '(5 (3 (1 () ()) ()) (9 (7 () ()) (11 () ())))) 

(tree->list-1 fig2-16-1)
(tree->list-2 fig2-16-1)