SICP 問題 2.30
(define (square-tree tree) (cond ((null? tree) nil) ((not (pair? tree)) (* tree tree)) (else (cons (square-tree (car tree)) (square-tree (cdr tree)))))) (define (square-tree tree) (map (lambda (sub-tree) (if (pair? sub-tree) (square-tree sub-tree) (* sub-tree sub-tree))) tree))