an convert the passed
    exception. Exceptions raised by the printer are ignored.
<p>

    When converting an exception into a string, the printers will be invoked
    in the reverse order of their registrations, until a printer returns
    a <code class="code"><span class="constructor">Some</span> s</code> value (if no such printer exists, the runtime will use a
    generic printer).
</p><p>

    When using this mechanism, one should be aware that an exception backtrace
    is attached to the thread that 