<TT><I>h</I></TT> is not a hole, <TT>Hole</TT> is raised.</P>
    </DD>

    <DT>
      <TT>fail (<I>h</I>, <I>ex</I>)</TT>
    </DT>
    <DD>
      <P>Requests the exception <TT><I>ex</I></TT>, fails the
      future associated with the hole <TT><I>h</I></TT> with <TT><I>ex</I></TT>,
      and fills the hole with the same failed future.
      If <TT><I>h</I></TT> is not a hole, <TT>Hole</TT> is raised.
      Equivalent to</P>
      <PRE>
        (Future.await <I>ex</I>; fill (<I>h</I>, spawn raise <I>ex</I