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Wait for events and use time

Plan bodies are suspend functions running on coroutines, so an intention can pause, for some time or until something happens, without blocking the agent: its other intentions keep running meanwhile.

Complete example

The wait-for-events example; run it with ./gradlew :examples:wait-for-events:run.

Wait for some time​

Use delay from kotlinx.coroutines:

} triggers {
    delay(1.seconds)
}
tip

In Alchemist simulations, delay and the timeouts of wait advance in simulated time.

Wait for an event​

agent.wait(filter, timeout) suspends the intention until the agent receives an event for which filter returns a non-null value, and returns that value; after timeout, it returns null. The filter is called on each event the agent handles while the intention waits: returning null means "not this one", and the intention keeps waiting for the next event. The filter sees every event the agent handles: belief and goal events (AgentEvent.Internal), as well as incoming messages and perceptions (AgentEvent.External).

private fun beliefAdded(expected: String): (AgentEvent) -> String? = { event ->
    ((event as? AgentEvent.Internal.Belief.Add<*>)?.belief as? String)?.takeIf { it == expected }
}
} triggers {
    val parcel = agent.wait(beliefAdded("parcel"), timeout = 5.seconds)
    if (parcel != null) agent.print("Parcel received!") else agent.print("Gave up waiting")
}

Put it together​

The two initial goals of the example run in two intentions: one waits for the parcel while the other delivers it.

To start intentions from a plan, or to wait for a sub-goal, see Achieve sub-goals and recover from failures.