1 665c255d 2023-08-04 jrmu (define (sum-odd-squares tree)
 2 665c255d 2023-08-04 jrmu   (cond ((null? tree) 0)
 3 665c255d 2023-08-04 jrmu 	((not (pair? tree))
 4 665c255d 2023-08-04 jrmu 	 (if (odd? tree) (square tree) 0))
 5 665c255d 2023-08-04 jrmu 	(else (+ (sum-odd-squares (car tree))
 6 665c255d 2023-08-04 jrmu 		 (sum-odd-squares (cdr tree))))))
 7 665c255d 2023-08-04 jrmu 
 8 665c255d 2023-08-04 jrmu (define (even-fibs n)
 9 665c255d 2023-08-04 jrmu   (define (next k)
10 665c255d 2023-08-04 jrmu     (if (> k n)
11 665c255d 2023-08-04 jrmu 	'()
12 665c255d 2023-08-04 jrmu 	(let ((f (fib k)))
13 665c255d 2023-08-04 jrmu 	  (if (even? f)
14 665c255d 2023-08-04 jrmu 	      (cons f (next (1+ k)))
15 665c255d 2023-08-04 jrmu 	      (next (1+ k))))))
16 665c255d 2023-08-04 jrmu   (next 0))
17 665c255d 2023-08-04 jrmu 
18 665c255d 2023-08-04 jrmu (map square (list 1 2 3 4 5))
19 665c255d 2023-08-04 jrmu 
20 665c255d 2023-08-04 jrmu (define (filter predicate sequence)
21 665c255d 2023-08-04 jrmu   (cond ((null? sequence) '())
22 665c255d 2023-08-04 jrmu 	((predicate (car sequence))
23 665c255d 2023-08-04 jrmu 	 (cons (car sequence)
24 665c255d 2023-08-04 jrmu 	       (filter predicate (cdr sequence))))
25 665c255d 2023-08-04 jrmu 	(else (filter predicate (cdr sequence)))))
26 665c255d 2023-08-04 jrmu 
27 665c255d 2023-08-04 jrmu (filter odd? (list 1 2 3 4 5))
28 665c255d 2023-08-04 jrmu (define (accumulate op initial sequence)
29 665c255d 2023-08-04 jrmu   (if (null? sequence)
30 665c255d 2023-08-04 jrmu       initial
31 665c255d 2023-08-04 jrmu       (op (car sequence)
32 665c255d 2023-08-04 jrmu 	  (accumulate op initial (cdr sequence)))))
33 665c255d 2023-08-04 jrmu (accumulate + 0 (list 1 2 3 4 5))
34 665c255d 2023-08-04 jrmu (accumulate * 1 (list 1 2 3 4 5))
35 665c255d 2023-08-04 jrmu (accumulate cons nil (list 1 2 3 4 5))
36 665c255d 2023-08-04 jrmu 
37 665c255d 2023-08-04 jrmu (define (enumerate-interval low high)
38 665c255d 2023-08-04 jrmu   (if (low > high)
39 665c255d 2023-08-04 jrmu       '()
40 665c255d 2023-08-04 jrmu       (cons low (enumerate-interval (1+ low) high))))
41 665c255d 2023-08-04 jrmu (define (enumerate-tree tree)
42 665c255d 2023-08-04 jrmu   (cond ((null? tree) '())
43 665c255d 2023-08-04 jrmu 	((not (pair? tree)) (list tree))
44 665c255d 2023-08-04 jrmu 	(else (append (enumerate-tree (car tree))
45 665c255d 2023-08-04 jrmu 		      (enumerate-tree (cdr tree))))))
46 665c255d 2023-08-04 jrmu (enumerate-tree (list 1 (list 2 (list 3 4)) 5))
47 665c255d 2023-08-04 jrmu 
48 665c255d 2023-08-04 jrmu (define (sum-odd-squares tree)
49 665c255d 2023-08-04 jrmu   (accumulate +
50 665c255d 2023-08-04 jrmu 	      0
51 665c255d 2023-08-04 jrmu 	      (map square
52 665c255d 2023-08-04 jrmu 		   (filter odd?
53 665c255d 2023-08-04 jrmu 			   (enumerate-tree tree)))))
54 665c255d 2023-08-04 jrmu (define (even-fibs n)
55 665c255d 2023-08-04 jrmu   (accumulate cons
56 665c255d 2023-08-04 jrmu 	      nil
57 665c255d 2023-08-04 jrmu 	      (filter even?
58 665c255d 2023-08-04 jrmu 		      (map fib
59 665c255d 2023-08-04 jrmu 			   (enumerate-interval 0 n)))))