popArg :: Peg Value
popArg = do PegState s (x:a) w n c b p <- get
            put $ PegState s a w n c b p
            return x
popArg :: Peg Value
popArg = do PegState s (x:a) w n c b p <- get
            put $ PegState s a w n c b p
            return x
popArg = do PegState s (x:a) w n c b p <- get
            put $ PegState s a w n c b p
            return x