text: class Functor:
      def __rrshift__(self, f):
          return self.fmap(f)
  
      @classmethod
      def unit(cls, x):
          raise NotImplementedError('unit not defined')
  
      def fmap(self, f):
          raise NotImplementedError('fmap not defined')
  
  
  def unit(cls, x):
      return cls.unit(x)
  