scala filter a list based on the values of another list
<p>I have two lists:</p>

<pre><code>val l1 = List(1, 2, 3, 4)
val l2 = List(true, false, true, true)
</code></pre>

<p>Is there a nice and short way to filter <code>l1</code> based on <code>l2</code>? </p>

<p><code>ris = List(1, 3, 4)</code></p>