sicp 2.18

 

Exercise 2.18.  Define a procedure reverse that takes a list as argument and returns a list of the same elements in reverse order:

 

 

(reverse (list 1 4 9 16 25))
(25 16 9 4 1)

 

 

 

 

(define (reverse items)
  (if (null? items)
      '()
      (append (reverse (cdr items)) (list (car items)))))

(define (append list1 list2)
  (if (null? list1)
      list2
      (cons (car list1) (append (cdr list1) list2))))

(reverse (list 1 4 9 16 25))