title: Bluebird coroutine usage
body: <p>I am attempting to use Bluebird's coroutines as follows:</p>
  
  <pre class="lang-js prettyprint-override"><code>var p = require('bluebird');
  //this should return a promise resolved to value 'v'
  var d = p.coroutine(function*(v) { yield p.resolve(v); });
  //however this prints 'undefined'
  d(1).then(function(v){ console.log(v); });
  </code></pre>
  
  <p>What is incorrect here?</p>