@do(ContinuationMonad)
    def react(self, handler):
        try:
            message = self.messages.popleft()
        except __HOLE__:
            self.handlers.append(handler)
            done(ContinuationMonad.zero())
        else:
            yield handler(message)
dataset/ETHPy150Open celery/cell/cell/workflow/common.py/Mailbox.react