title: Why binding not exhaustive?
body: <p>Why <code>binding not exhaustive</code> warning on the last line? </p>
  
  <pre><code>datatype fruit = Apple
  datatype sizedFruit = Big of fruit | Small of fruit
  val Big x = Big Apple;
  </code></pre>
  
  <p>I think the binding IS exhaustive because the RHS expression matches the LHS pattern with <code>x = Apple</code> on the one and only given case. Hence, could I safely ignore this warning? </p>
  
  <p>The warning goes away by replacing line 2 with <code>datatype sizedFruit = Big of fruit</code>, but my real use case can't afford this. Thanks in advance.</p>
  
  <p><em>Compiler: Standard ML of New Jersey (64-bit) v110.96</em></p>