s called with the next
        available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.
      </dd>
      <dt>op</dt>
      <dd> A binary operation of the form <i>op</i>(<i>r</i>, <i>state</i>).&nbsp;
        This operation is expanded by <b>BOOST_PP_FOR</b> with the next
        available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.&nbsp;
        This macro is repeatedly applied to the <i>state</i>, each time
        producing a new <i>state</i>, until <i>pred</i> returns <i>0