import tensorflow as tf

      tf.float32, size=self.num_cells + 2, clear_after_read=False)
    arc_seq = tf.TensorArray(tf.int32, size=self.num_cells * 4)
    if prev_c is None:
      assert prev_h is None, "prev_c and prev_h must both be None"
      prev_c = [tf.zeros([1, self.lstm_size], tf.float32)
                for _ in range(self.lstm_num_layers)]
      prev_h = [tf.zeros([1, self.lstm_size], tf.float32)
                for _ in range(self.lstm_num_layers)]
    inputs = self.g_emb

    for layer_id in range(2):
      next_c, next_h = stack_lstm(inputs, prev_c, prev_h, self.w_lstm)
