Some Simple Examples

Author: Wishnu Prasetya

Below are several simple examples of how to write agents with aplib. They are just simple examples and won’t do anything spectacular. It is recommended that you first go through the Tutorial-1 and Tutorial-2 to become familiar with some basic concepts (e.g. action and goal) of aplib agent programming.

Example: guess-number agent

This agent plays a simple number-guessing game. The user is asked to think of an integer x in the interval of 0..10. The agent then interacts with the user, trying to guess x.

Goal

The goal is to get the user to answer with “y” (short for “yes”), signalling that the agent has guessed x correctly, or if the agent concludes that the user cheats by having x outside the 0..10 range:

goal("the-goal").toSolve((String p) -> p.equals("y") || p.equals("out of range")) 		

Agent’s state

Our agent will maintain a boolean array excluded and sets excluded[i] = true if it thinks that x cannot be equal to i. To support this, we will use the following state structure:

static public class MyAgentState extends SimpleState {
   boolean[] excluded = ... // initialized to falses ;
   ...

Agent’s actions

The action below checks if there are still numbers in 0..10 that could be x. It chooses one randomly, and offers it to the user, asking if it is indeed x.

var guess = action("guess")
    . do1((MyAgentState belief) -> {
        // the agent performs some inference:
        var candidates = belief.getPossibilities() ;
        if(candidates.isEmpty()) {
           belief.env().println("Your number is NOT in [0..10]!") ;
           return "out of range" ;
        }
        int x = candidates.get(belief.rnd.nextInt(candidates.size())) ;
        var o = belief.env().ask("Is it " + x + "? (answer y/n)") ;
        belief.excluded[x] = true ;
        return o ;	 
    })
    ...

The action below asks if the user can give a hint in the form of a lower bound for x:

var asklb = action("askLowerBound")
    . do1((MyAgentState belief) -> {
        var o = belief.env().ask("Type a number less or equal to your number:");
        var i = toInt(o) ;
        if (i!=null) {
           for (int k=0; k<Math.max(0,i); k++)
                belief.excluded[k] = true ;
        }
        return "" ;
      })
      ...

Tactic to solve the goal

To solve the previously given goal (or any goal), the agent will need a tactic. The following tactic will first ask a hint from the user (in the form of a lower bound for x), and then it will make a guess:

SEQ(asklb,guess)

If after the guess action the goal is not solved, the agent will implicitly repeat the above tactic at the next tick, on and on, until the goal is solved.

Full code

The full code of this example can be found here