def build_fake_controller(cell):
  """Create a scalar variable to track the timestep.

  Args:
    cell: The NeuralStackCell to add the variable to.
  """
  cell.current_step = cell.add_variable(
      "current_step", [],
      initializer=tf.constant_initializer(-1),
      dtype=tf.int32,
      trainable=False)
Create a scalar variable to track the timestep.

  Args:
    cell: The NeuralStackCell to add the variable to.
  
tensor2tensor/models/research/neural_stack_test.py