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{{draft task}}In [[Remote agent]], a game is described where an agent interacts with a simple world of walls, balls and squares, and a component is described that marshals commands between the simulation environment and the logic code behind the agent.

The goal conditions for the game are to get all balls in squares of matching colors, in as few turns as possible.

Using an [[Remote agent/Agent interface|interface]] for your language write a program that attempts to reach these goals. The exact agent behavior within the simulated environment is unspecified.


See [[Remote agent/Simulation/C]]


package agent

import (


// The agent's awareness is quite limited.  It has no representation of the
// maze, which direction it is facing, or what it did last.  It notices and
// remembers just three things:  The color of the sector just entered, the
// presense and color of any ball there, and the presense and color of any
// ball it is holding.
var sectorColor, sectorBall, agentBall byte

// Package level variable to simplify function calls.
var stream ifc.Streamer

func Agent(s ifc.Streamer) {
    stream = s
    // randomness used for movement
    // handshake
    hs := stream.Rec()
    if hs != ifc.Handshake {
        log.Fatal("agent: thats no handshake")
    // agent behavior main loop
    for gameOver := false; !gameOver; {
        gameOver = drop()

// noColor is not part of the interface or the world's representation.
// It is used by the agent as a test for receipt of a color-based event.
const noColor byte = '-'

// Move moves one sector in a random direction.
// It retries on bumps and doesn't return until a forward command succeeds.
// It expects a color event on a successful move and terminates if it doesn't
// get one.
func move() {
    for {
        // Randomness:  50/50 chance of turning or attempting move.
        // For turns, equal chance of turning right or left.
        switch rand.Intn(4) {
        case 0:
            for stream.Rec() != ifc.EvStop {
        case 1:
            for stream.Rec() != ifc.EvStop {
        bump := false
        sectorColor = noColor
        sectorBall = noColor
        for {
            switch ev := stream.Rec(); ev {
            case ifc.EvBump:
                bump = true
            case ifc.EvColorRed, ifc.EvColorGreen,
                ifc.EvColorYellow, ifc.EvColorBlue:
                sectorColor = ev
            case ifc.EvBallRed, ifc.EvBallGreen,
                ifc.EvBallYellow, ifc.EvBallBlue:
                sectorBall = ev
            case ifc.EvStop:
                break events
        if bump {
        if sectorColor == noColor {
            log.Fatal("agent: expected color event after move")

// FindMisplaced wanders the maze looking for a ball on the wrong sector.
func findMisplaced() {
    for {
        // get ball from current sector if meaningful
        switch sectorBall {
        case ifc.EvBallRed, ifc.EvBallGreen,
            ifc.EvBallYellow, ifc.EvBallBlue:
            if sectorBall != sectorColor+32 {

// Get is only called when get is possible.
func get() {
    for {
        switch stream.Rec() {
        case ifc.EvStop:
            // agent notes ball color, and that sector is now empty
            agentBall = sectorBall
            sectorBall = noColor
        case ifc.EvNoBallInSector, ifc.EvAgentFull:
            log.Fatal("agent: expected get to succeed")

// There's a little heuristic built in to findMatching and drop.
// Ideally, findMatching finds an empty sector matching the ball that the
// agent is holding and then drop drops it there.  FindMatching returns
// with partial success however, if it finds a sector matching the ball
// where the sector is not empty, but contains a ball of the wrong color.
// In this case, drop will drop the ball on the nearest empty sector,
// in hopes that it has at least moved the ball near a sector where it
// might ultimately go.

// FindMatching is only called when agent has a ball.
// FindMatching finds a sector where the color matches the ball the agent
// is holding and which does not already contain a matching ball.
// It does not necessarily find an empty matching sector.
func findMatching() {
    for sectorColor+32 != agentBall || agentBall == sectorBall {

// Drop is only called when the agent has a ball.  Unlike get() however,
// drop() can be called whether the sector is empty or not.  drop() means
// drop as soon as possible, so if the sector is full, drop() will wander
// at random looking for an empty sector.
func drop() (gameOver bool) {
    for sectorBall != noColor {
    // expected to work
    for {
        switch stream.Rec() {
        case ifc.EvGameOver:
            gameOver = true
        case ifc.EvStop:
            break ev
        case ifc.EvNoBallInAgent, ifc.EvSectorFull:
            log.Fatal("expected drop to succeed")
    sectorBall = agentBall
    agentBall = noColor


See [[Remote agent/Agent_logic/Julia]]


[[/PicoLisp|Implementation in PicoLisp]].


Sample agent (''not'' a good or smart player of the game; just to show how to program to the interface). {{works with|Tcl|8.6}}

package require Tcl 8.6
package require RC::RemoteAgent

oo::class create Agent {
    superclass AgentAPI
    variable sectorColor ballColor
    forward Behavior my MoveBehavior

    # How to move around
    method MoveBehavior {} {
	set ball ""
	while 1 {
	    try {
		while {rand() < 0.5} {
		    my ForwardStep
		    my BallBehavior
	    } trap bumpedWall {} {}
	    if {rand() < 0.5} {
		my TurnLeft
	    } else {
		my TurnRight
	set ::wonGame ok

    # How to handle the ball once we've arrived in a square
    method BallBehavior {} {
	upvar 1 ball ball anywhere anywhere
	if {
	    $ball eq ""
	    && $ballColor ne ""
	    && $ballColor ne $sectorColor
	} then {
	    set ball [set ballTarget $ballColor]
	    set anywhere 0
	    my GetBall
	} elseif {
	    $ball ne ""
	    && ($ball eq $sectorColor || $anywhere)
	} {
	    try {
		if {[my DropBall]} {
		    return -code break
		set ball ""
	    } trap sectorFull {} {
		# Target square full; drop this ball anywhere
		set anywhere 1

Agent new "localhost" 12345
vwait wonGame