code: def result(self, res):
          '''Return a value according to the parameter `res` when parse successfully.'''
          return self >> Parser(lambda _, index: Value.success(index, res)f result(self, res):
          '''Return a value according to the parameter `res` when parse successfully.'''
          return self >> Parser(lambda _, index: Value.success(index, res))
docs: Return a value according to the parameter `res` when parse successfully.