1 (define (test-case actual expected)
2   (newline)
3   (display "Actual:   ")
4   (display actual)
5   (newline)
6   (display "Expected: ")
7   (display expected)
8   (newline))
9 
10 (define (accumulate op initial sequence)
11   (if (null? sequence)
12       initial
13       (op (car sequence)
14 	  (accumulate op initial (cdr sequence)))))
15 
16 (define (horner-eval x coefficient-sequence)
17   (accumulate (lambda (coefficient remaining-horner) 
18 		(+ coefficient
19 		   (* x remaining-horner)))
20 	      0
21 	      coefficient-sequence))
22 
23 ;; (test-case (horner-eval 0 '()) 0)
24 ;; (test-case (horner-eval 10 '()) 0)
25 ;; (test-case (horner-eval 0 '(1)) 1)
26 ;; (test-case (horner-eval 2 '(1 3 0 5 0 1)) 79)
27 ;; (test-case (horner-eval -1 '(2 4 1 1 8 3)) 3)
28 ;; (test-case (horner-eval 1.23 '(3 5 2 9 4)) 38.079068639999996)
29 
30 ;; Exercise 2.35.  Redefine count-leaves from section 2.2.2 as an accumulation:
31 
32 (define (count-leaves t)
33   (accumulate + 0 (map (lambda (subtree)
34 			 (cond ((null? subtree) 0)
35 			       ((not (pair? subtree)) 1)
36 			       (else (count-leaves subtree))))
37 		       t)))
38 
39 (test-case (count-leaves '()) 0)
40 (test-case (count-leaves '(((())) () (() (())))) 0)
41 (test-case (count-leaves '(2 3 0 9 8)) 5)
42 (test-case (count-leaves '((2) (1 (2 5 (8 (9) 3) 2)) 4)) 9)