solution to 2.54

diff --git a/src/sicp/ex2_54.clj b/src/sicp/ex2_54.clj
new file mode 100644 (file)
index 0000000..0039c29
--- /dev/null
+++ b/src/sicp/ex2_54.clj
@@ -0,0 +1,27 @@
+(ns sicp.ex2_54
+  (:use [clojure.test]))
+
+(defn atom? [x]
+  (not (list? x)))
+
+(defn eq? [x y]
+  (if (not (atom? x))
+    false
+    (= x y)))
+
+(defn equal? [a b]
+  (cond (empty? a) (empty? b)
+        (atom? (first a))
+        (if (eq? (first a) (first b))
+          (equal? (rest a) (rest b))
+          false)
+        :else (and (equal? (first a) (first b))
+                   (equal? (rest a) (rest b)))))
+
+(deftest test-equality
+  (are [x y] [= x y]
+       (equal? '(1) '(1)) true
+       (equal? '(1) '(2)) false
+       (equal? '(1 2) '(1 2)) true
+       (equal? '(1 2 (3)) '(1 2 (3))) true
+       (equal? '(1 2 3) '(1 2 (3))) false))
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