为什么caddr [(ABC)] = C？

Question

理想情况下,在LISP中:

caddr[(A B C)] = car[cdr[cdr[(A B C)]]] = car[cdr[(B C)]] = car[C] = Undefined.

但该书说答案是C.有人可以解释一下吗？

非常感谢.

Answer 1

你的错误是cdr [(BC)]是列表(C),而不是原子C.

然后车[(C)]是C.

Answer 2

(cdr'(bc))是列表(c),而不是原子c,所以表达式变为(car'(c))而不是(car c)

? (cdr '(b c))
(C)

? (car '(c))
C