('compile') -->
</div>
<div class="section" id="optional-parameters">
<h4>2.1.5.2&nbsp;&nbsp;&nbsp;Optional Parameters</h4>
<div class="compound">
<p class="compound-first">Optional parameters—nested in an <tt class="docutils literal">(optional … )</tt> clause—are given
as a series of adjacent <em>three</em>-element tuples describing the
parameter name, any requirements on the argument type, <em>and</em> and an
expression representing the parameter's default value:</p>
<pre class="compound-last litera