unbind nm = modify $ \(PegState s a w n c b p) -> PegState s a (M.delete nm w) n c b p
unbind nm = modify $ \(PegState s a w n c b p) -> PegState s a (M.delete nm w) n c b p
unbind nm = modify $ \(PegState s a w n c b p) -> PegState s a (M.delete nm w) n c b p