Add some simple examples for multimethods

resources/koans.clj

@@ -280,4 +280,9 @@
                           [2 4]
                           [2 4]
                           6]}]
+
+ ["27_multimethods" {"__" ["Hello, World!"
+                           "Hello there"
+                           1
+                           6]}]
 ]

src/koans/27_multimethods.clj

@@ -0,0 +1,44 @@
+(ns koans.27-multimethods
+  (:require [koan-engine.core :refer :all]))
+
+(defmulti multimethod-without-args
+ (fn [keyword-arg] keyword-arg))
+
+(defmethod multimethod-without-args :first [_]
+ (str "Hello, World!"))
+
+(defmethod multimethod-without-args :second [_]
+ (str "Hello there"))
+
+(defmulti multimethod-with-args
+ (fn [opt-one opt-two] opt-one))
+
+(defmethod multimethod-with-args :path-one [_ opts]
+ (:first-opt opts))
+
+(defmethod multimethod-with-args :path-two [_ opts]
+ (let [numbers (:second-opt opts)]
+  (->> numbers
+       (map inc)
+       (reduce +))))
+
+(defmethod multimethod-with-args :path-three [_])
+
+(meditations
+ "A multimethod takes an one or more arguments to dispatch on"
+ (= __
+    (multimethod-without-args :first))
+
+ "Though it can be ignored and represented by _ in defmethods"
+ (= __
+    (multimethod-without-args :second))
+
+ "Alternatively, we can use the arguments in defmethods"
+ (= __
+    (multimethod-with-args :path-one {:first-opt 1
+                                      :second-opt 2}))
+ 
+ "This allows us to something different in each method implementation"
+ (= __
+    (multimethod-with-args :path-two {:first-opt 1
+                                      :second-opt [0 1 2]})))