title: What is the API for PersistentQueue?
body: <p>What is the API for PersistentQueue?</p>
  
  <p>Naïvely, it appears to lose any data put into it:</p>
  
  <pre><code>user=&gt; (def q (into (clojure.lang.PersistentQueue/EMPTY)
                      (repeat 5 nil)))
  #'user/q
  user=&gt; (def q2 (pop (conj q :a)))
  #'user/q2
  user=&gt; (get q2 4)
  nil
  user=&gt; (get q2 0)
  nil
  </code></pre>
  
  <p>I must not be accessing PersistentQueue correctly. Clearly it doesn't work with <code>get</code>. What is the right way to access a PersistentQueue? What <em>can</em> you do with it?</p>
  
  <p>And is PersistentQueue documented anywhere, even informally? ("It's only fully documented in my answer" is fine. Really, I'm hoping that someone will write the missing documentation in an answer, or tell where to find it if it's not missing.)</p>