add more exercise

resources/koans.clj

@@ -83,6 +83,7 @@
                                   ()
                                   [:anything :goes :here]
                                   (< x 31)
+                                  [2 4 6 8]
                                   (* 10 x) (< x 4)
                                   24
                                   100

src/koans/08_higher_order_functions.clj

@@ -17,6 +17,9 @@
   "Or somewhere in between"
   (= [10 20 30] (filter (fn [x] __) [10 20 30 40 50 60 70 80]))
 
+  "It all depends on what you want, you can also use a prefined function"
+  (= __ (filter even? [1 2 3 4 5 6 7 8]))
+
   "Maps and filters may be combined"
   (= [10 20 30] (map (fn [x] __) (filter (fn [x] __) [1 2 3 4 5 6 7 8])))