title: Combine multiple variants into one variant
body: <p>Is there a way to combine multiple variants together into one? Something like this:</p>
  
  <pre><code>type pet = Cat | Dog;
  type wild_animal = Deer | Lion;
  type animal = pet | wild_animal;
  </code></pre>
  
  <p>This is a syntax error, but I would like animal to become a variant with four constructors: <code>Cat | Dog | Deer | Lion</code>. Is there a way to do this?</p>