p>
          For other distributions, like the normal distribution, it is obviously
          very useful to provide 'standard' defaults for the mean (zero) and standard
          deviation (unity) thus:
        </p>
<pre class="programlisting"><span class="identifier">normal_distribution</span><span class="special">(</span><span class="identifier">RealType</span> <span class="identifier">mean</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="iden