tree-map¶

; `scale-tree` procedure
(define (scale-tree tree factor)
    (cond ((null? tree) tree)
          ((not (pair? tree)) (* factor tree))
          (else (cons (scale-tree (car tree) factor)
                      (scale-tree (cdr tree) factor)))))

(scale-tree (list 1 (list 2 (list 3 4) 5) (list 6 7)) 10)
; (10 (20 (30 40) 50) (60 70))

; `scale-tree` using `map`
(define (scale-tree tree factor)
    (map (lambda (sub-tree)
            (if (pair? sub-tree)
                (scale-tree sub-tree factor)
                (* sub-tree factor)))
         tree))

(scale-tree (list 1 (list 2 (list 3 4) 5) (list 6 7)) 10)
; (10 (20 (30 40) 50) (60 70))