title: Alias for variables in pattern matching
body: <p>I often have something similar to the following (standard type definition for trees):</p>
  
  <pre><code>match tree with
      | Branch(v, Branch(vl, tll, tlr), _) = f Branch(vl, tll, tlr)
  </code></pre>
  
  <p>In other languages there is the ability to do something like:</p>
  
  <pre><code>match tree with
      | Branch(v, tl@Branch(_, _, _), _) = f tl
  </code></pre>
  
  <p>Does OCaml have something similar?</p>