title: Extracting value from Option with match gives "unable to infer enough type information..." error
body: <p>I'm trying simply to convert an inputted string into an integer. I know this can be done by applying <code>unwrap</code> to <code>from_str</code> but I figured I'd try to handle the error case properly and extract the value with a match instead. Instead of it working as expected I just get this error... </p>
  
  <blockquote>
    <p>error: unable to infer enough type information about <code>_</code>; type annotations required<code>which points to the</code>x<code>in</code>Some(x)`</p>
  </blockquote>
  
  <pre><code>fn main () {
      let ref num = os::args()[1];
      match from_str(num.as_slice()) {
          Some(x) =&gt; println!("{}", x),
          None =&gt; println!("string cannot be converted to int"),
      }
  }
  </code></pre>
  
  <p>What am I missing?</p>