Exercise 2.21 · 习题

Exercise 2.21: The procedure square-list
takes a list of numbers as argument and returns a list of the squares of those
numbers.

(square-list (list 1 2 3 4))
(1 4 9 16)

Here are two different definitions of square-list. Complete both of
them by filling in the missing expressions:

(define (square-list items)
(if (null? items)
nil
(cons ⟨??⟩ ⟨??⟩)))

(define (square-list items)

(map ⟨??⟩ ⟨??⟩))

练习 2.21：过程 square-list 以一个数的表为参数，返回由这些数的平方构成的表。

(square-list (list 1 2 3 4))
(1 4 9 16)

以下是 square-list 的两种不同定义。通过填入缺失的表达式，补全这两个定义：

(define (square-list items)
(if (null? items)
nil
(cons ⟨??⟩ ⟨??⟩)))

(define (square-list items)
(map ⟨??⟩ ⟨??⟩))