Generate a sequence.

        Parameters
        ----------
        state : `str` or `iterable` of `str`
            Initial state.
        size : `int`
            State size.
        dataset : `str`
            Dataset key.
        backward : `bool`, optional
            Link direction.

        Returns
        -------
        `generator` of `str`
            Node value generator.

def generate(self, state, size, dataset, backward=False):
        """Generate a sequence.

        Parameters
        ----------
        state : `str` or `iterable` of `str`
            Initial state.
        size : `int`
            State size.
        dataset : `str`
            Dataset key.
        backward : `bool`, optional
            Link direction.

        Returns
        -------
        `generator` of `str`
            Node value generator.
        """
        if isinstance(state, str):
            state = self.split_state(state)
        state = self.get_state(state, size)
        dataset = self.get_dataset(dataset)
        while True:
            link, state = self.random_link(dataset, state, backward)
            if link is None or backward and link == '':
                return
            yield link