Created by: Superjomn

with break_if

input = pd.data(...)
num_steps = Var(12)

TensorArray states(size=num_steps)
TensorArray step_inputs(unstack_from=input)
TensorArray step_outputs(size=num_steps)

W = Tensor(...)
U = Tensor(...)
default_state = some_op()

step = Var(1)

wloop = paddle.create_whileloop(loop_vars=[step])
with wloop.frame():
    wloop.break_if(pd.equal(step, num_steps)
    pre_state = states.read(step-1, default_state)
    step_input = step_inputs.read(step)
    state = pd.sigmoid(pd.matmul(U, pre_state) + pd.matmul(W, step_input))
    states.write(step, state)
    step_outputs.write(step, state) # output state
    step.update(state+1)

output = step_outputs.stack()