list - 只能通过使用 cons car cdr

Question

如何仅使用以下三个函数从列表中获取第 2 到第 7 个元素:

cons

car

cdr

例子;

> (two-to-seven (list 8 9 5 1 0 3 6 2 4))
> (9 5 1 0 3 6)

谢谢。

Answer 1

> (define (t2s xs)
    (cons (car (cdr xs)) (cons (car (cdr (cdr xs))) (cons (car (cdr (cdr (cdr xs)))) (cons (car (cdr (cdr (cdr (cdr xs))))) (cons (car (cdr (cdr (cdr (cdr (cdr xs)))))) (cons (car (cdr (cdr (cdr (cdr (cdr (cdr xs))))))) (list))))))))
> (t2s (list 8 2 5 4 0 3 6 1 1))
(2 5 4 0 3 6)