( map square '(2 3) )
(cons (square 2) (map square '(3)) )
(cons 4 '(9) )
'( 4 9 )
(define (map f x)
(cond ((null? x) nil)
(else (cons (f (car x)) (map f (cdr x)))) ))
( map square '(2 3) )の評価は '( 4 9 )