This interpreter does not understand  <i>quote</i>  or  <i>'</i>. When you write<p><pre><code>  (cdr '(ddd a xxx))
</code></pre>
the interpreter reads<p><pre><code>  (  cdr  '(  ddd  a  xxx  )  )
           | 
           \------  '(  is a token
</code></pre>
For example, this works:<p><pre><code>  (cdr (list 1 2 3))</code></pre>