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)
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| (define nil '()) | |
| (define (append list1 list2) | |
| (if (null? list1) | |
| list2 | |
| (cons (car list1) (append (cdr list1) list2)))) | |
| (define (reverse list1) | |
| (if | |
| (null? list1) | |
| nil | |
| (if | |
| (null? (cdr list1)) | |
| list1 | |
| (append | |
| (reverse (cdr list1)) | |
| (cons (car list1) nil))))) | |
| (reverse (list 1 2)) | |
| (reverse (list 1 2 3 4 5)) | |
| (reverse (list 1)) | |
| (reverse ()) | |
| (reverse '()) | |