Add update-gs, which always returns the modified gs and is almost always what you want.

src/hottub/gs.clj

@@ -14,6 +14,9 @@
 (defmacro with-gs [gs & body]
   `(binding [*gamestate* (ref ~gs)] (dosync ~@body)))
 
+(defmacro update-gs [& body]
+  `(with-gs ~@body (get-gs)))
+
 (defn get-gs [] @*gamestate*)
 
 (defn entity-in [gamestate id] (get-in gamestate [:entities id]))
@@ -80,4 +83,4 @@
     (defmethod query-index indextype [indextype index query] (or (get index query) #{}))))
 
 (define-id-index :name)
-(define-id-index :type)
+(define-id-index :type)