Very rough sketch of a beginning, not even nearly doing anything interesting.

src/cljs/mw3/core.cljs

@@ -1,18 +1,70 @@
-(ns mw3.core
+(ns ^:figwheel-always mw3.core
   (:require [om.core :as om :include-macros true]
-            [om.dom :as dom :include-macros true]))
+            [om.dom :as dom :include-macros true]
+            [cljs.core.async :refer [put! chan <!]]
+            [clojure.string :as string]))
 
 (enable-console-print!)
 
-(defonce app-state (atom {:text "Hello Chestnut!"}))
+;; The state of the application.
+;; NOTE that app-state can contain vectors and maps only, not lists.
+(defonce app-state (atom {:available-tabs {:#home-tab :#home-content
+                                           :#params-tab :#params-content
+                                           :#rules-tab :#rules-content
+                                           :#world-tab :#world-content
+                                           :#docs-tab :#docs-content}
+                          :selected-tab :#home-tab
+                          :text "Welcome to MicroWorld!"
+                          :rules []
+                          :params {:available-rulesets []
+                                   :available-heightmaps []
+                                   :ruleset ""
+                                   :heightmap ""}
+                          :world []}))
 
-(defn root-component [app owner]
+(deref app-state)
+(:available-tabs (deref app-state))
+
+(defn root-component [data owner]
   (reify
     om/IRender
     (render [_]
-      (dom/div nil (dom/h1 nil (:text app))))))
+      (dom/div nil (dom/h1 nil (:text data))))))
+
+(defn tab-bar [data owner]
+  (reify
+    om/IInitState
+    (init-state [_]
+      {:selected-tab :#home-tab
+       :selected-content :#home-content})
+    om/IRender
+    (render [this]
+            (dmu/ul nil
+                    )))
+
+
+(def pages [:#home-content :#params-content :#rules-content :#world-content :#docs-content])
+
+(defn onclick-handler
+  "Handles a click on the specified `tab` and reveals the specified `content`."
+  [tab content]
+  (doseq [page pages]
+          (dommy/hide!(sel page)))
+  (dommy/show! content))
+
+;; NASTY! Javascript interprets hyphens as subtraction operators, so function names
+;; exposed to raw Javascript (e.g. onclick event handlers) must not contain hyphens.
+
+(defn ^:export home []
+  (onclick-handler :#home-tab :#home-content))
+
+(defn ^:export params []
+  (onclick-handler :#params-tab :#params-content))
+
 
 (om/root
  root-component
  app-state
- {:target (. js/document (getElementById "app"))})
+ {:target (. js/document (getElementById "world-content"))})
+
+