Is it possible to have a parameter that depends on parameters at the previous time step using the dynamic time functionality of param?

For example, I want to model a bathtub.

```
import param as pm
class BathTub(pm.Parameterized):
x = pm.Magnitude(0.5, doc="The level of water in the bathtub")
k = pm.Number(0.1, bounds=(0, None), doc="The width of the drain")
def step(self):
self.x -= self.k * self.x
b = BathTub(x=lambda pm.Dynamic.time())
```

Obviously the way i’m instantiated BathTub with dynamic time is not correct, but I can’t conceptually think about how to do it correctly. Is it possible to model complex systems with the param time module?

I would really appreciate hearing from @philippjfr on the matter consider the implementation of: topographica/topo/base/simulation.py at master · ioam/topographica · GitHub

Thanks!