SICP_2.53-2.55

 1 #lang racket
 2 
 3 ;;;;;;;;;;;;;;;;;;2.53
 4 (define (memq item x)
 5   (cond ((null? x) false)
 6         ((eq? item (car x)) x)
 7         (else (memq item (cdr x)))))
 8 
 9 (list ‘a ‘b ‘c)
10 
11 (list (list ‘george))
12 
13 (cdr ‘((x1 x2) (y1 y2)))
14 
15 (cadr ‘((x1 x2) (y1 y2)))
16 
17 (pair? (car ‘(a short list)))
18 
19 (memq ‘red ‘((red shoes) (blue socks)))
20 
21 (memq ‘red ‘(red shoes blue socks))
22 
23 ;;;;;;;;;;;;;;;2.54
24 (define (equal? a b)
25   (cond ((and (pair? a) (pair? b)
26               (equal? (car a) (car b))
27               (equal? (cdr a) (cdr b)))
28          true)
29         ((eq? a b) true)
30         (else false)))
31 
32 ;;;;;;;;;;;;;test
33 (equal? ‘(this is a list) ‘(this is a list))
34 
35 (equal? ‘(this is a list) ‘(this (is a) list))
36 
37 ;;;;;;;;;;;;;;2.55
38 (car ‘‘abracadara)
39 
40 (car ‘(quoto abracadara))