title: How do I conditionally execute code only when an Option is None?
body: <p>I don't want to take action if the function returns a value in the optional; how do I test the <code>None</code> case only?  This code works, but it looks horrible.        </p>
  
  <pre><code>let v = ffunc();
  match v {
    None =&gt; { callproc() }, 
    Some(x) =&gt; {  }
  }
  </code></pre>
  
  <p>In C, I can write:</p>
  
  <pre class="lang-none prettyprint-override"><code>int x = ffunc();
  if ( !x ) { callproc() } 
  </code></pre>