From: Ramakrishnan Muthukrishnan <vu3rdd@gmail.com>
Date: Mon, 2 Aug 2010 13:51:45 +0000 (+0530)
Subject: added parts of section 2.2.3
X-Git-Url: https://git.rkrishnan.org/pf/content/using.html?a=commitdiff_plain;h=8bf66a6f688a8af8f7c38156c50e7116bd9286e8;p=sicp.git

added parts of section 2.2.3
---

diff --git a/src/sicp/ch1_2.clj b/src/sicp/ch1_2.clj
index 1021953..bcf0dba 100644
--- a/src/sicp/ch1_2.clj
+++ b/src/sicp/ch1_2.clj
@@ -1,5 +1,5 @@
 (ns sicp.ch1-2
-  (:use [sicp utils]
+  (:use [sicp.utils :only (square)]
 	[clojure.contrib.math :only (sqrt expt)]
 	[clojure.contrib.trace :only (dotrace)]))
 
@@ -166,19 +166,20 @@
     (mygcd b (rem a b))))
 
 ;;; section 1.2.6 Primality testing.
-(defn prime? [n]
-  (= (smallest-divisor n) n))
-
-(defn smallest-divisor [n]
-  (find-divisor n 2))
+(defn divides? [a b]
+  (= (rem b a) 0))
 
 (defn find-divisor [n test-divisor]
   (cond (> (square test-divisor)  n) n
 	(divides? test-divisor n) test-divisor
 	:else (find-divisor n (inc test-divisor))))
 
-(defn divides? [a b]
-  (= (rem b a) 0))
+(defn smallest-divisor [n]
+  (find-divisor n 2))
+
+(defn prime? [n]
+  (= (smallest-divisor n) n))
+
 
 ;; fermat's little theorem
 (defn expmod [base exp m]
@@ -188,12 +189,12 @@
 	:else (rem (* base (expmod base (dec exp) m))
 		   m)))
 
-(defn fermat-test [n]
-  (try-it (+ 1 (rand-int (- n 1))) n))
-
 (defn try-it [a n]
   (= a (expmod a n n)))
 
+(defn fermat-test [n]
+  (try-it (+ 1 (rand-int (- n 1))) n))
+
 (defn fast-prime? [n times]
   (cond (= times 0) true
 	(fermat-test n) (fast-prime? n (dec times))
diff --git a/src/sicp/ch2_2.clj b/src/sicp/ch2_2.clj
index e0107f5..21d9f33 100644
--- a/src/sicp/ch2_2.clj
+++ b/src/sicp/ch2_2.clj
@@ -1,5 +1,6 @@
-(ns sicp.ch2_2
-  (:refer-clojure :exclude (map)))
+(ns sicp.ch2-2
+  (:refer-clojure :exclude (map))
+  (:use (sicp [ch1-2 :only (fib)])))
 
 (cons 1
       (cons 2
@@ -104,4 +105,54 @@
 	 (if (seq? sub-tree)
 	   (scale-tree-with-map sub-tree factor)
 	   (* sub-tree factor)))
-       tree))
\ No newline at end of file
+       tree))
+
+;;; 2.2.3
+(defn sum-odd-squares [tree]
+  (cond (nil? tree) 0
+	(not (seq? tree)) (if (odd? tree)
+			    ((fn [x] (* x x)) tree)
+			    0)
+	:else (+ (sum-odd-squares (first tree))
+		 (sum-odd-squares (next tree)))))
+
+(defn even-fibs [n]
+  (letfn [(next-fib [k]
+		    (if (> k n)
+		      nil
+		      (let [f (fib k)]
+			(if (even? f)
+			  (cons f (next-fib (+ k 1)))
+			  (next-fib (+ k 1))))))]
+    (next-fib 0)))
+
+(map #(* % %) (list 1 2 3 4 5))
+
+(defn myfilter-1 [pred? xs]
+  (cond (nil? xs) nil
+	(not (seq? xs)) (if (pred? xs)
+			  (list xs)
+			  ())
+	:else (concat (myfilter-1 pred? (first xs))
+		      (myfilter-1 pred? (next xs)))))
+
+(defn myfilter-2 [pred? xs]
+  (cond (nil? xs) nil
+	(pred? (first xs)) (cons (first xs)
+				 (myfilter-2 pred? (next xs)))
+	:else (myfilter-1 pred? (next xs))))
+
+;; accumulate
+(defn accumulate [op init xs]
+  (if (nil? xs)
+    init
+    (op (first xs)
+	(accumulate op init (next xs)))))
+
+(defn enumerate-interval
+  ([high]
+     (enumerate-interval 0 high))
+  ([low high]
+     (if (> low high)
+       nil
+       (cons low (enumerate-interval (+ low 1) high)))))
\ No newline at end of file