title: How to provide a default value for a function argument in ATS?
body: <p>Say I have a function declared as follows:</p>
  
  <pre><code>fun foo(x: int, y: bool): string
  </code></pre>
  
  <p>I would like to write <code>foo(x)</code> to mean <code>foo(x, false)</code>. Is there a way to
  support this in ATS?</p>