call observers in parent nodes

just/observable-test.fnl

@@ -49,3 +49,11 @@
   (s:observe [:foo] #(set win true))
   (s:update [:foo :bar] 42)
   (expect (and win)))
+
+(let [s (observable.new {:foo {:bar {:baz 43}}})]
+  (var win 0)
+  ;; observers on ancestor trees are called after child trees
+  (s:observe [:foo] #(set win (/ win 2)))
+  (s:observe [:foo :bar] #(set win 4))
+  (s:update [:foo :bar :baz] 42)
+  (expect (= win 2)))

just/observable.fnl

@@ -6,7 +6,10 @@
 (fn update [data self path value]
   (let [[first & rest] path]
     (if (next rest)
-        (update (. data first) self rest value)
+        (do
+          (update (. data first) self rest value)
+          (if data._subscribers
+              (each [_ f (pairs data._subscribers)] (f))))
         (do
           (if data._subscribers
               (each [_ f (pairs data._subscribers)] (f)))