Koan for agents

resources/koans.clj

@@ -203,4 +203,9 @@
                         5
                         :hello
                         (6 :this :are)
-                        ]}]]
+                        ]}]
+ ["21_agents" {"__" [true
+                     10
+                     10
+                     12
+                     IllegalStateException]}]]

src/koans/21_agents.clj

@@ -0,0 +1,31 @@
+(def agent-example
+  "Agents provide shared access to mutable state."
+  (agent 10))
+
+(meditations
+  "Creating an Agent is as simple as assigning it a value"
+  (= __ (instance? clojure.lang.Agent agent-example))
+
+  "To get agent's value you dereference it"
+  (= __ @agent-example)
+
+  "To set a new value, you use send or send-all functions, but you can't just send anything.."
+  (= __ (do
+          (set-error-mode! agent-example :continue)
+          (send agent-example 20)
+          @agent-example))
+
+  "Send takes a function and arguments and sends them to the agent. The send function,
+   returns immediately, but the action is prccessed in a separate thread and it's the result,
+   of that action that gets assigned to agent's state"
+  (= __ (do
+          (send agent-example + 2)
+          @agent-example))
+
+  "You can create validations for states that agent is allowed to take"
+  (= __ (do
+          (set-validator! agent-example #(even? %))
+          (try
+            (send agent-example + 1)
+            (catch IllegalStateException e))
+          (agent-error agent-example))))