title: Why is my variable "undefined"?
body: <p>Why is my variable <code>nodes</code> undefined in the vector-push-extend line?</p>
  
  <pre><code>(defun make_graph (strings)
    (defparameter nodes (make-array 0))
    (loop for x in strings do
         (vector-push-extend (make-instance 'node :data x) nodes))
  n)
  </code></pre>