solution to 2.5

diff --git a/src/sicp/ex2_5.clj b/src/sicp/ex2_5.clj
new file mode 100644 (file)
index 0000000..95a04c3
--- /dev/null
+++ b/src/sicp/ex2_5.clj
@@ -0,0 +1,36 @@
+(ns sicp.ex2_5
+  (:use [sicp utils]
+       [clojure.test]))
+
+(defn my-cons [x y]
+  (* (int (Math/pow 2 x))
+     (int (Math/pow 3 y))))
+
+(defn- power-of-n* [x n cnt]
+  (let [q (quot x n)
+       r (rem x n)]
+    (if (= r 0)
+      (power-of-n* (quot x n) n (inc cnt))
+      cnt)))
+
+(defn car [x]
+  (power-of-n* x 2 0))
+
+(defn cdr [x]
+  (let [p3 (quot x (Math/pow 2 (car x)))]
+    (power-of-n* p3 3 0)))
+
+(deftest test-car-for-various-cons-cell-values
+  (let [c1 (my-cons 2 3)
+       c2 (my-cons 2 0)
+       c3 (my-cons 0 0)
+       c4 (my-cons 0 1)]
+    (are [p] [= p true]
+        (and (= (car c1) 2)
+             (= (cdr c1) 3))
+        (and (= (car c2) 2)
+             (= (cdr c2) 0))
+        (and (= (car c3) 0)
+             (= (cdr c3) 0))
+        (and (= (car c4) 0)
+             (= (cdr c4) 1)))))