adding about map/filter/reduce

koans/about_higher_order_functions.clj

@@ -0,0 +1,32 @@
+(meditations
+  "The map function relates a sequence to another"
+  (= [__ __ __] (map (fn [x] (* 4 x)) [1 2 3]))
+
+  "You may create that mapping"
+  (= [1 4 9 16 25] (map (fn [x] __) [1 2 3 4 5]))
+
+  "Or use the names of existing functions"
+  (= __ (map nil? [:a :b nil :c :d]))
+
+  "A filter can be strong"
+  (= __ (filter (fn [x] false) '(:anything :goes :here)))
+
+  "Or very weak"
+  (= '(:anything :goes :here) (filter (fn [x] __) '(:anything :goes :here)))
+
+  "Or somewhere in between"
+  (= [10 20 30] (filter (fn [x] __) [10 20 30 40 50 60 70 80]))
+
+  "Maps and filters may be combined"
+  (= [10 20 30] (map (fn [x] __) (filter (fn [x] __) [1 2 3 4 5 6 7 8])))
+
+  "Reducing can increase the result"
+  (= __ (reduce (fn [a b] (* a b)) [1 2 3 4]))
+
+  "You can start somewhere else"
+  (= 2400 (reduce (fn [a b] (* a b)) __ [1 2 3 4]))
+
+  "Numbers are not the only things one can reduce"
+  (= "longest" (reduce (fn [a b]
+                         (if (< __ __) b a))
+                       ["which" "word" "is" "longest"])))

koans/path_to_enlightenment.clj

@@ -18,4 +18,5 @@
 (load "about_maps")
 (load "about_functions")
 (load "about_conditionals")
+(load "about_higher_order_functions")
 (println "You have acheived clojure enlightenment. Namaste.")