Unrolls the recurrent cell for one time step.

        Parameters
        ----------
        inputs : sym.Variable
            Input symbol, 2D, of shape (batch_size * num_units).
        states : list of sym.Variable
            RNN state from previous step or the output of begin_state().

        Returns
        -------
        output : Symbol
            Symbol corresponding to the output from the RNN when unrolling
            for a single time step.
        states : list of Symbol
            The new state of this RNN after this unrolling.
            The type of this symbol is same as the output of `begin_state()`.
            This can be used as an input state to the next time step
            of this RNN.

        See Also
        --------
        begin_state: This function can provide the states for the first time step.
        unroll: This function unrolls an RNN for a given number of (>=1) time steps.

def forward(self, inputs, states):
        """Unrolls the recurrent cell for one time step.

        Parameters
        ----------
        inputs : sym.Variable
            Input symbol, 2D, of shape (batch_size * num_units).
        states : list of sym.Variable
            RNN state from previous step or the output of begin_state().

        Returns
        -------
        output : Symbol
            Symbol corresponding to the output from the RNN when unrolling
            for a single time step.
        states : list of Symbol
            The new state of this RNN after this unrolling.
            The type of this symbol is same as the output of `begin_state()`.
            This can be used as an input state to the next time step
            of this RNN.

        See Also
        --------
        begin_state: This function can provide the states for the first time step.
        unroll: This function unrolls an RNN for a given number of (>=1) time steps.
        """
        # pylint: disable= arguments-differ
        self._counter += 1
        return super(RecurrentCell, self).forward(inputs, states)