span><span class=identifier>rule </span><span class=special>= </span><span class=identifier>an_arbitrarily_complex_expression</span><span class=special>;</span></font></code></pre>
<p>without having to know or care about the resulting type of the right-hand side 
  (rhs) of the assignment expression. Apart from this, we also need a facility 
  to forward declare an unknown type:</p>
<pre><code><font color="#000000"><span class=special>    </span><span class=identifier>T </span><span class=identifier>rule</s