title: How do you declare and use a Set data structure in groovysh?
body: <p>I've tried: </p>
  
  <pre><code>groovy:000&gt; Set&lt;String&gt; s = ["a", "b", "c", "c"]
  ===&gt; [a, b, c]
  groovy:000&gt; s
  Unknown property: s
  </code></pre>
  
  <p>I want to be able to use this as a set, but even if I pass it explicitly, it turns it into an ArrayList:</p>
  
  <pre><code>groovy:000&gt; joinList(["a", "b", "c", "c"])
  ERROR groovy.lang.MissingMethodException:
  No signature of method: groovysh_evaluate.joinList() is applicable for argument types: (java.util.ArrayList) values: [[a, b, c, c]]
  Possible solutions: joinList(java.util.Set)
  </code></pre>