code: def next(self):
          
          self.current_token = next(self.token_stream, None)
          if self.current_token is None:
              self.token_span = self.token_span[1], self.token_span[1]
              raise self.error('Unexpected end of input')
          self.token_span = self.current_token.span
          return self
docs: Move to the next token in the token stream.