~join t` reduces the term by reducing each leaf to `init`, and at each node of the syntax tree, using `join` to merge the values. In a top-down traversal, if `case` returns `Some a` then the subterm is not recrusively reduced, but the value `a` is used instead.</p></div></div><div class="odoc-spec"><div class="spec value" id="val-transform" class="anchored"><a href="#val-transform" class="anchor"></a><code><span><span class="keyword">val</span> transform : 
  <span>case:<span>( <span><span>( <span><a href="