observes_that

[hlamothe]

Hello! I'm experimenting with memo's "observes_that" to condition on runtime values. It works when "observes_that" is at the end (right before the return), but I'm trying to use it earlier and then reference the observed value later in the code.

I want to observe an action specified at runtime, then use that observed value in a later "thinks" block (e.g., pass it to another agent's knows statement).

For example:

observer: observes_that [alice.a0 == {obs_actions[0]}]
observer: thinks[
env: knows([alice.a0])
env: ...
]

Is this a valid way to use "observes_that"? If so, what's the correct syntax to reference the observed value (e.g., [alice.a0] vs something else)?

[hlamothe]

I answered my own question! It looks like I can just keep referencing the observed value (to be specified at runtime) in the rest of the memo code.

observer: observes_that [alice.a0 == {obs_actions[0]}]
observer: thinks[
env: knows({obs_actions[0]})
env: ...
]

[kach]

Hi Herrissa,

Actually, all agents always know the value of model parameters like obs_actions. So, you don't need to write env: knows(…) anything at all: your model should still work if you removed it.

In fact, you discovered a little bug in memo, which I just fixed. The only valid inputs to knows(…) are names of choices like a0 or alice.a0 — you can't pass in arbitrary values like {obs_actions[0]}. memo was silently ignoring that malformed statement, but in the next version, it will explicitly give an error message explaining what's wrong.

But that's just a detail. In short, you should be fine with your current solution — just drop the knows line!

By the way, the code in your initial message was very close to being correct. Instead of env: knows([alice.a0]), you should write env: knows(alice.a0) (no square brackets). This would let env access alice.a0. But again, your current solution of just directly referencing {obs_actions[0]} also works.

Finally, just a note. In general, I would recommend using array_index(obs_actions, 0) instead of {obs_actions[0]}. It should be equivalent but slightly faster and more robust.