SICP問題2.31
直接バージョン
(define (tree-map proc items) (cond ((null? items) (list)) ((not (pair? items)) (proc items)) (else (cons (tree-map proc (car items)) (tree-map proc (cdr items))))))
map と再帰バージョン
(define (tree-map proc tree) (map (lambda (sub-tree) (if (pair? sub-tree) (tree-map proc sub-tree) (proc sub-tree))) tree))