Add a recursive list processing example.

src/koans/recursion.clj

@@ -4,10 +4,15 @@
       (___ (is-even? (dec n)))))
 
 (defn is-even-bigint? [n]
-  (loop [n n acc true]
-    (if (= n 0) __
+  (loop [n   n
+         acc true]
+    (if (= n 0)
+        __
         (recur (dec n) (not acc)))))
 
+(defn recursive-reverse [coll]
+  __)
+
 (defn factorial [n]
   __)
 
@@ -21,6 +26,12 @@
   "Having too many stack frames requires explicit tail calls with recur"
   (= false (is-even-bigint? 100003N))
 
+  "Reversing directions is easy when you have not gone far"
+  (= '(1) (recursive-reverse [1]))
+
+  "Yet more difficult the more steps you take"
+  (= '(5 4 3 2 1) (recursive-reverse [1 2 3 4 5]))
+
   "Simple things may appear simple."
   (= 1 (factorial 1))