Add matches and nested APIs

machine.js

@@ -119,6 +119,10 @@ export function invoke(fn, ...transitions) {
     });
 }
 
+export let nested = (to, states) => invoke(createMachine(states, identity),
+  transition('done', to)
+);
+
 let machine = {
   get state() {
     return {
@@ -172,6 +176,14 @@ function send(service, event) {
 }
 
 let service = {
+  matches(query) {
+    let states = query.split('.'), matched = false, service = this;
+    do {
+      matched = !!service && states.shift() === service.machine.current;
+      service = service.child;
+    } while(matched && states.length);
+    return matched;
+  },
   send(event) {
     this.machine = send(this, event);
 

test/test-invoke.js

@@ -1,4 +1,4 @@
-import { createMachine, immediate, interpret, invoke, reduce, state, state as final, transition } from '../machine.js';
+import { createMachine, immediate, interpret, invoke, nested, reduce, state, state as final, transition } from '../machine.js';
 
 QUnit.module('Invoke', hooks => {
   QUnit.module('Promise');
@@ -275,4 +275,30 @@ QUnit.module('Invoke', hooks => {
 
     service.send('next');
   });
+
+  QUnit.test('matches() matches the state', async assert => {
+    const machine = createMachine({
+      one: state(
+        transition('next', 'two')
+      ),
+      two: nested('three', {
+        alpha: state(
+          transition('next', 'beta')
+        ),
+        beta: state()
+      }),
+      three: state()
+    });
+
+    let service = interpret(machine, () => {});
+    assert.equal(service.matches('one'), true, 'is the first state');
+    assert.equal(service.matches('two.alpha'), false, 'not in the child state');
+
+    service.send('next');
+    assert.equal(service.matches('two'), true, 'is in the two state');
+    assert.equal(service.matches('two.alpha'), true, 'in the alpha state');
+
+    service.child.send('next');
+    assert.equal(service.matches('three'), true, 'In the last state');
+  });
 });