d</code> is a pending stream, because its parent <code>b</code> is also pending.</p>
<p>This also applies to dependent streams created via <code>stream.map</code>:</p>
<pre><code class="lang-javascript">var value = stream()
var doubled = value.map(function(value) {return value * 2})

console.log(doubled()) // logs undefined because `doubled` is pending
</code></pre>
<h4 id="active-state"><a href="#active-state">Active state</a></h4>
<p>When a stream receives a value, it becomes active (unless the stream is 