title: Why is `a = a` `nil` in Ruby?
body: <p>I watched this <a href="https://www.destroyallsoftware.com/talks/wat">video</a>. Why is <code>a = a</code> evaluated to <code>nil</code> if <code>a</code> is not defined?</p>
  
  <pre><code>a = a # =&gt; nil
  b = c = q = c # =&gt; nil
  </code></pre>