example.py

@tagged
class Maybe(object):
  @construct
  def Nothing(self):
    pass
  @construct
  def Just(self, data: int):
    pass
  
  
  Maybe = attr.union('Maybe')
  
  @Maybe.register
  @attr.s
  class Nothing(object):
    def map(self, func):
      return self
      
  @Maybe.register
  @attr.s
  class Just(object):
    data = attr.ib()
    def map(self, func):
      return Just(func(self.data))