[ACT-R-users] stopping pm

[Christian Lebiere]

> If there is no chunk in the goal buffer, ACT-R will halt.  Thus, if you
> do a !pop!, ACT-R will stop once there's nothing in the event queue.
> This may not be the "Christian & Dan approved" way of stopping ACT-R, but
> it's effective.

It is not as much a matter of a seal of approval as looking at theoretical 
coherence and forward compatibility.  Since the goal is just another buffer 
now there is really no reason to stop the system when the goal is empty as 
when any other buffer is empty, which happens all the time.  More 
practically, the trick worked because without a goal you were assured that 
no production could fire.  But now, productions don't have to match the 
goal so even without a goal a production could fire that sets a new goal. 
So  while the trick might still work now,  who knows for how long?

> Other production systems (e.g. OPS5), do have an explicit RHS HALT
> operator. Perhaps we ought to consider such a thing for ACT-R 6.0.

There is a RHS !stop! operator.  It should still work for (run) but not 
(pm-run), but we could try to generalize it to that effect.  Of course, 
that assumes that we want to hang on to the !bang! syntax, or else find a 
suitable alternative.

Christian