solution to 2.2 with tests

diff --git a/src/sicp/ex2_2.clj b/src/sicp/ex2_2.clj
new file mode 100644 (file)
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+++ b/src/sicp/ex2_2.clj
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+(ns sicp.ex2_2
+  (:use [sicp utils]
+       [clojure.test]))
+
+(defn make-segment [x y]
+  (list x y))
+
+(defn start-segment [seg]
+  (first seg))
+
+(defn end-segment [seg]
+  (first (rest seg)))
+
+(defn make-point [x y]
+  (list x y))
+
+(defn x-point [p]
+  (first p))
+
+(defn y-point [p]
+  (first (rest p)))
+
+(defn midpoint-segment [seg]
+  (let [x1 (x-point (start-segment seg))
+       y1 (y-point (start-segment seg))
+       x2 (x-point (end-segment seg))
+       y2 (y-point (end-segment seg))]
+    (make-point (average x1 x2)
+               (average y1 y2))))
+
+
+(deftest test-mid-point-1-1-3-3
+  (let [m (midpoint-segment (make-segment  (make-point 1 1)
+                                          (make-point 3 3)))]
+    (are [x y] [approx-equal x y]
+        (x-point m) 2.0
+        (y-point m) 2.0)))
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