2.31¶

; 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))

(define (tree-map f tree)
    (map (lambda (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)))
;Value 2: (1 (4 (9 16) 25) (36 49))