code></a> functor constructs implementations for any type, given a
   <code class="code">compare</code> function.
   For instance:</p>
<pre class="codepre"><code class="code">     <span class="keyword">module</span> <span class="constructor">IntPairs</span> =
       <span class="keyword">struct</span>
         <span class="keyword">type</span> t = int * int
         <span class="keyword">let</span> compare (x0,y0) (x1,y1) =
           <span class="keyword">match</span> <span class="constructor">Pervasives</