SICP Exercise 2.31

sicp

Question

Abstract your answer to exercise 2.30 to produce a procedure tree-map with the property that square-tree could be defined as

(define (square-tree tree)
  (tree-map square tree))

Answer

(define (tree-map f tree)
  (map (λ (sub-tree)
         (if (pair? sub-tree)
             (tree-map f sub-tree)
             (f sub-tree)))
         tree))

(define (square-tree tree)
  (tree-map square tree))

(square-tree (list 1
                     (list 2 (list 3 4) 5)
                     (list 6 7)))

Results:

(1 (4 (9 16) 25) (36 49))