val create : ?pos:Positions.pos ‑> Base.unit ‑> tCreate a new parser state. pos is the initial position, it defaults to
{line=1;col=0;offset=0}.
val reset : ?pos:Positions.pos ‑> t ‑> Base.unitReset the given parsing state. The following always succeed:
        reset t ?pos;
        assert (t = create ?pos ())
      val position : t ‑> Positions.pos