sicp 2.21

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 <??> <??>))

 

 

(define (square-list items)
  (if (null? items)
      nil
      (cons (square (car items)) (square-list (cdr items)))))

(define (square-list items)
  (map square items))