title: DrRacket: atom? and symbol? undefined - What's wrong?
body: <p>I'm learning programming in Lisp using DrRacket. I don't like it too much but I would like to pass my exam ;)</p>
  <p>I have a weird problem - I can't use the <code>atom?</code> and <code>symbol?</code> functions. But <code>number?</code> and <code>string?</code> both work fine.</p>
  <pre class="lang-lisp prettyprint-override"><code>&gt; (atom? '())
  . . atom?: undefined;
   cannot reference an identifier before its definition
  &gt; (symbol? A)
  . . A: undefined;
   cannot reference an identifier before its definition
  &gt; 
  </code></pre>
  <p>Am I doing something wrong? If not, what's the problem?</p>
  <p>I'm using DrRacket 6.0.1 on Mac.</p>