Fix infinite loop in has binder

README.md

@@ -161,6 +161,16 @@ expect(foo.a.b).toBe(50); // new one updated
 expect(a.b).toBe(30); // from before it was orphaned
 ```
 
+### Strings
+
+String concatenation is straightforward.
+
+```javascript
+var object = {name: "world"};
+bind(object, "greeting", {"<-": "'hello ' + name + '!'"});
+expect(object.greeting).toBe("hello world!");
+```
+
 ### Sum
 
 Some advanced queries are possible with one-way bindings from
@@ -858,7 +868,7 @@ expect(object.hasNeedle).toBe(true);
 
 `has` bindings are not incremental, but with the right data-structure,
 updates are cheap.  The [Collections][] package contains Lists, Sets,
-and OrderedSets that all can send content change notifications and thus
+and OrderedSets that all can send ranged content change notifications and thus
 can be bound.
 
 ```javascript
@@ -868,6 +878,19 @@ object.haystack = new Set([1, 2, 3]);
 expect(object.hasNeedle).toBe(true);
 ```
 
+Likewise, Maps implement `addMapChangeListener`, so you can use a `has` binding
+to observe whether an entry exists with the given key.
+
+```javascript
+// Continued from above...
+var Map = require("collections/map");
+object.haystack = new Map([[1, "a"], [2, "b"]]);
+object.needle = 2;
+expect(object.hasNeedle).toBe(true);
+object.needle = 3;
+expect(object.hasNeedle).toBe(false);
+```
+
 `has` bindings can also be left-to-right and bi-directional.
 
 ```javascript

observe.js

@@ -45,9 +45,9 @@ function observe(source, expression, descriptorOrFunction) {
             return descriptor.change.apply(source, arguments);
         } else if (typeof contentChange === "function") {
             value.addRangeChangeListener(contentChange);
-            return Observers.once(function () {
+            return function () {
                 value.removeRangeChangeListener(contentChange);
-            });
+            };
         }
     }), sourceScope);
 }