Dan's Thoughts Thinking somewhat carefully

Exercise 2.21 of SICP

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)
    '()
    (cons 
      ((lambda (x) (* x x))
       (car items))
      (square-list (cdr items)))))
 
(define (square-list2 items)
  (map (lambda (x) (* x x)) items))

> (square-list (list 1 2 3 4 5))
(1 4 9 16 25)
> (square-list2 (list 1 2 3 4 5))
(1 4 9 16 25)