title: How do I get keepWhen behaviour in Elm 0.15?
body: <p>The <code>keepWhen</code> function from earlier versions of Elm was removed. I have ported an Elm application from 0.14, but I'm stuck at trying to get one part of it to work, where it's using <code>keepWhen</code>.</p>
  
  <p>So basically I'm looking for a function like</p>
  
  <pre><code>keepWhen : Signal Bool -&gt; a -&gt; Signal a -&gt; Signal a
  </code></pre>
  
  <p>I have found</p>
  
  <pre><code>filter : (a -&gt; Bool) -&gt; a -&gt; Signal a -&gt; Signal a
  </code></pre>
  
  <p>but it's not quite the same thing, and I haven't figured out how to get it to work.</p>