solution to 2.28. Really interesting..

diff --git a/src/sicp/ex2_28.clj b/src/sicp/ex2_28.clj
new file mode 100644 (file)
index 0000000..027b285
--- /dev/null
+++ b/src/sicp/ex2_28.clj
@@ -0,0 +1,19 @@
+(ns sicp.ex2_28
+  (:use [clojure.test]))
+
+;; take a list of nested lists and return a flat list with elements
+;; in the same left-to-right order
+(defn fringe [lst]
+  (cond (not (seq? lst)) (list lst)
+       (empty? lst)     nil
+       :else (concat (fringe (first lst))
+                     (fringe (rest lst)))))
+
+(deftest test-fringe-with-simple-list
+  (is (= (fringe '(1 2 3 4)) '(1 2 3 4))))
+
+(deftest test-fringe-with-nested-list
+  (are [x y] [= x y]
+       (fringe '((1 2) 3 4))   '(1 2 3 4)
+       (fringe '(1 2 (3 4)))   '(1 2 3 4)
+       (fringe '((1 2) (3 4))) '(1 2 3 4)))