var serial_maker = function () {
    var preifx = ‘‘;
    var seq = 0;
    return {
      set_prefix: function (p) {
        preifx = String(p);
      },
      set_seq: function (s) {
        seq = s;
      },
      gensym: function () {
        var result = preifx + seq;
        seq++;
        return result
      }
    }
  }
  var maker = serial_maker();
  maker.set_prefix(Q);
  maker.set_seq(100);
  var unique = maker.gensym(); // "Q100"