From: Ramakrishnan Muthukrishnan <vu3rdd@gmail.com>
Date: Sat, 27 Mar 2010 19:26:12 +0000 (+0530)
Subject: new file for section 1.2
X-Git-Url: https://git.rkrishnan.org/listings/using.html?a=commitdiff_plain;h=51f7aa601b3641c9d225120c4df1fb292dee145d;p=sicp.git

new file for section 1.2
---

diff --git a/chapter1/ch1_2.clj b/chapter1/ch1_2.clj
new file mode 100644
index 0000000..6780735
--- /dev/null
+++ b/chapter1/ch1_2.clj
@@ -0,0 +1,54 @@
+(ns sicp.chapter1.ch1_2
+  (:use (clojure.contrib trace)))
+
+
+(defn factorial [n]
+  (if (= n 1)
+    1
+    (* n (factorial (- n 1)))))
+
+;; stack friendly version
+(defn factorial2 [n]
+  (loop [x n acc 1] 
+    (if (= x 1)
+      acc
+      (recur (- x 1) (* acc x)))))
+
+;; even better
+(defn factorial3 [n]
+  (reduce * (range 1 (inc n))))
+
+(comment
+ user> (dotrace [factorial] (factorial 3))
+ TRACE t2701: (factorial 3)
+ TRACE t2702: |    (factorial 2)
+ TRACE t2703: |    |    (factorial 1)
+ TRACE t2703: |    |    => 1
+ TRACE t2702: |    => 2
+ TRACE t2701: => 6
+ 6
+)
+
+(comment
+  sicp.chapter1.ch1_2> (dotrace [factorial] (factorial 6))
+  TRACE t2778: (factorial 6)
+  TRACE t2779: |    (factorial 5)
+  TRACE t2780: |    |    (factorial 4)
+  TRACE t2781: |    |    |    (factorial 3)
+  TRACE t2782: |    |    |    |    (factorial 2)
+  TRACE t2783: |    |    |    |    |    (factorial 1)
+  TRACE t2783: |    |    |    |    |    => 1
+  TRACE t2782: |    |    |    |    => 2
+  TRACE t2781: |    |    |    => 6
+  TRACE t2780: |    |    => 24
+  TRACE t2779: |    => 120
+  TRACE t2778: => 720
+  720
+  )
+
+(comment
+  sicp.chapter1.ch1_2> (dotrace [factorial2] (factorial2 6))
+  TRACE t2806: (factorial2 6)
+  TRACE t2806: => 720
+  720
+  )
\ No newline at end of file