From: Ramakrishnan Muthukrishnan <vu3rdd@gmail.com>
Date: Sun, 30 May 2010 12:53:46 +0000 (+0530)
Subject: a much beautiful way to solve 1.43 using recursion
X-Git-Url: https://git.rkrishnan.org/?a=commitdiff_plain;h=d28d1e53f2d99b4024e3f9310fd56c2777677409;p=sicp.git

a much beautiful way to solve 1.43 using recursion
---

diff --git a/src/sicp/ex1_43.clj b/src/sicp/ex1_43.clj
index 5c8e7ea..ae29dff 100644
--- a/src/sicp/ex1_43.clj
+++ b/src/sicp/ex1_43.clj
@@ -4,13 +4,19 @@
 	[sicp ch1_3]
 	[sicp ex1_42]))
 
-(defn- repeated-1 [f1 f2 m]
+;; older iterative implementation
+(defn- repeated-i [f1 f2 m]
   (cond (= m 0) f1
 	(= m 1) f2
-	:else (repeated-1 f1 (compose f2 f1) (- m 1))))
+	:else (repeated-i f1 (compose f2 f1) (- m 1))))
+
+(defn repeated-iterative [f n]
+  (repeated-i f (compose f f) (- n 1)))
 
 (defn repeated [f n]
-  (repeated-1 f (compose f f) (- n 1)))
+  (if (= n 1)
+    f
+    (compose f (repeated f (- n 1)))))
 
 (deftest test-repeated-square-twotimes-of-5
   (is (= ((repeated square 2) 5)
@@ -19,3 +25,6 @@
 (deftest test-repeated-square-twotimes-of-2
   (is (= ((repeated square 2) 2)
 	 16)))
+
+(deftest test-repeated-inc-of-2-by-5
+  (is (= ((repeated inc 5) 2) 7)))
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