;; IN: a Tree, a function of one argument
;; OUT: a Tree, result of applying input funct on
;;      every datum in the input Tree

(define (tree-map fn tree)
  (make-tree (fn (datum tree))
	(map (lambda (t) (tree-map fn t)) (children tree))))






;; map definition:
(define (map fn ls)
  (if (null? ls) '()
      (cons (fn (car ls)) (map fn (cdr ls)))))





;; mutual recursion version

(define (tree-map fn tree)
  (make-tree (fn (datum tree))
	 (tree-map-f fn (children tree))))

(define (tree-map-f fn forest)
  (if (null? forest) '()
      (cons (tree-map fn (car forest))
	    (tree-map-f fn (cdr forest)))))