on) -&gt; unit</code></pre><div class="info ">
<code class="code"><span class="constructor">Printexc</span>.register_printer fn</code> registers <code class="code">fn</code> as an exception
    printer.  The printer should return <code class="code"><span class="constructor">None</span></code> or raise an exception
    if it does not know how to convert the passed exception, and <code class="code"><span class="constructor">Some</span>
    s</code> with <code class="code">s</code> the resulting string if it c