solution and tests for exercise 2.1

diff --git a/src/sicp/ex2_1.clj b/src/sicp/ex2_1.clj
new file mode 100644 (file)
index 0000000..9020280
--- /dev/null
+++ b/src/sicp/ex2_1.clj
@@ -0,0 +1,30 @@
+(ns sicp.ex2_1
+  (:use [sicp ch2_1 utils]
+       [clojure.test]))
+
+;; the gcd version of make-rat does this automatically for us. But assuming
+;; we don't use gcd, here is the solution
+(defn new-make-rat [x y]
+  (cond (and (< x 0) (< y 0)) (list (- x) (- y))
+       (or (< x 0) (< y 0)) (if (< x 0) (list x y) (list (- x) (- y)))
+       :else (list x y)))
+
+(deftest test-num-p-den-p
+  (are [x y] (= x y)
+       (numer (new-make-rat 2 3)) 2
+       (denom (new-make-rat 2 3)) 3))
+
+(deftest test-num-p-den-n
+  (are [x y] (= x y)
+       (numer (new-make-rat 2 -3)) -2
+       (denom (new-make-rat 2 -3)) 3))
+
+(deftest test-num-n-den-n
+  (are [x y] (= x y)
+       (numer (new-make-rat -2 -3)) 2
+       (denom (new-make-rat -2 -3)) 3))
+
+(deftest test-num-n-den-p
+  (are [x y] (= x y)
+       (numer (new-make-rat -2 3)) -2
+       (denom (new-make-rat -2 3)) 3))
\ No newline at end of file