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Agent Definition Introduction

To create our first agent, right click on the project and follow New > File. Name the file myproject.sarl.

The SARL default editor will open.

1. Basic agent definition

Agents are defined using the agent keyword.

agent MyAgent {
}

2. Package definition

SARL elements are organized in packages. You can define the package using the package keyword.

The following code will define an agent with a fully qualified name of io.sarl.docs.gettingstarted.^agent. The character ^ in the package name permits to use a SARL keyword into a package name.

The package keyword defines the package for all elements in the same SARL file (see the [General Syntax Reference](../reference/GeneralSyntax.html) for details). Therefore FirstAgent and SecondAgent belong to the same package, i.e. `io.sarl.docs.gettingstarted.^agent`.

3. Agent Perceptions

Agents need to perceive their environment in order to react to external stimuli. Perceptions take the form of events (see Event and Agent References for details).

3.1. Declare an Event

To declare a new event use the event keyword. The following code defines a new event MyEvent.

event MyEvent

3.2. Define an agent Perceptions

Now, we will want our agent to react to MyEvent and print a message on the console.

To define this event handler, we must use the on keyword, and provide the associated code block.

The `println` function is provided by the `Logging` capacity. It permits printing a message on the log output.
import io.sarl.core.Logging
agent MyAgent {
	uses Logging
	on MyEvent {
		println("Received MyEvent")
	}
}

3.3. Lifecycle events

SARL defines two lifecycle events :

This means that when agent has been spawned and it is ready to begin its execution, it will receive an Initialize event. You can react to this event just like with any other event defined in SARL.

Likewise, when the agent is going to stop its execution (we will see how to stop an agent later on), it will receive a Destroy Event. The purpose of this event is to release any system resource properly.

import io.sarl.core.Logging
import io.sarl.core.Initialize
import io.sarl.core.Destroy
agent MyAgent {
	uses Logging
	on Initialize {
		println("MyAgent spawned")
	}
	on Destroy {
		println("MyAgent destroyed")
	}
}

3.4. Accessing the event’s occurrence

Inside a behavior declaration you may need to access the event instance the agent is reacting to.

This instance is called an occurrence.

In the case of an Initialize events you can access the arguments for the agent spawn using occurrence.parameters).

import io.sarl.core.Logging
import io.sarl.core.Initialize
import io.sarl.core.Destroy
agent MyAgent {
	uses Logging
	on Initialize {
		println("MyAgent spawned")
		println("My Parameters are :" + occurrence.parameters.toString)
	}
	on Destroy {
		println("MyAgent destroyed")
	}
}

4. Agent Communication

Agents need to send data and stimuli to other agents. This communication takes the form of event sending (see Event and Agent References for details).

4.1. Use the capacity to send an event in the default space

Now, we will want our agent to send data to other agents. The data are embedded into events. The definition of an event is described above.

In this document, we limit our explanation to the sending of the events in the default space of the default context of the agent.

For sending an event in the default space, the DefaultContextInteractions built-in capacity should be used.

Below, we define an agent that is using this capacity.

import io.sarl.core.DefaultContextInteractions
agent MyAgent {
	uses DefaultContextInteractions
}

4.2. Send an event in the default space

The DefaultContextInteractions built-in capacity provides functions for sending events in the default space.

Below, we define an action in which an instance of MyEvent is created, and then sent into the default space with the function call emit(e).

agent MyAgent {
	uses DefaultContextInteractions
	def doSomething {
		var e = new MyEvent
		emit(e)
	}
}

5. What’s next?

In the next section, we will learn how to start a SARL agent in the Eclipse IDE.

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