Add 1.33

sicp-ex-1.33.rkt

@@ -0,0 +1,33 @@
+#! /usr/bin/racket
+#lang racket/base
+
+(define (square n)
+  (* n n))
+
+(define (smallest-divisor n)
+  (find-divisor n 2))
+
+(define (find-divisor n test-divisor)
+  (define (next iterator)
+    (if (= iterator 2) 3 (+ iterator 2)))
+  (cond ((> (square test-divisor) n) n)
+        ((divides? test-divisor n) test-divisor)
+        (else (find-divisor n (next test-divisor)))))
+
+(define (divides? a b)
+  (= (remainder b a) 0))
+
+(define (prime? n)
+  (= n (smallest-divisor n)))
+
+(define (filtered-accumulate combiner null-value predicate term a next b)
+  (define (iter a result)
+    (if (> a b)
+        result
+        (iter (next a) (combiner (if (predicate a) (term a) null-value) result))))
+  (iter a null-value))
+
+(define (range-sum-of-primes a b)
+  (filtered-accumulate + 0 prime? (lambda (x) x) a (lambda (x) (+ 1 x)) b))
+
+(range-sum-of-primes 2 10)