!  BestGuess makes the best guess it can out of the match list, assuming that
!  everything in the match list is textually as good as everything else;
!  however it ignores items marked as -1, and so marks anything it chooses.
!  It returns -1 if there are no possible choices.
! ----------------------------------------------------------------------------

[ BestGuess  earliest its_score best i;

  earliest=0; best=-1;
  for (i=0:i<number_matched:i++)
  {   if (match_list-->i >= 0)
      {   its_score=match_scores-->i;
          if (its_score>best) { best=its_score; earliest=i; }
      }
  }
#ifdef DEBUG;
  if (parser_trace>=4)
  {   if (best<0)
          print "   Best guess ran out of choices^";
      else
          print "   Best guess ", (the) match_list-->earliest,
                " (", match_list-->earliest, ")^";
  }
#endif;
  if (best<0) return -1;
  i=match_list-->earliest;
  match_list-->earliest=-1;
  bestguess_score = best;
  return i;
];