title: SML - How to create a list out of a postorder scan of a tree
body: <p>How to implement a function in SML which gets a tree and returns a list. The list consists of the values in the tree nodes according to postorder scan of the tree.</p>
  
  <p>The tree <code>datatype</code> is:</p>
  
  <pre><code>datatype 'a Tree = Leaf | Branch of 'a * 'a Tree * 'a Tree;
  </code></pre>