Solution to level 6 in Untrusted: http://alex.nisnevich.com/untrusted/

untrusted-lvl6-solution.js

/****************
 * drones101.js *
 ****************
 *
 * Do you remember, my dear Professor, a certain introductory
 * computational rationality class you taught long ago? Assignment
 * #2, behavior functions of autonomous agents? I remember that one
 * fondly - but attack drones are so much easier to reason about
 * when they're not staring you in the face, I would imagine!
 */

function startLevel(map) {
    function moveToward(obj, type) {
        var target = obj.findNearest(type);
        var leftDist = obj.getX() - target.x;
        var upDist = obj.getY() - target.y;

        var direction;
        if (upDist == 0 && leftDist == 0) {
        	return;
        } if (upDist > 0 && upDist >= leftDist) {
            direction = 'up';
        } else if (upDist < 0 && upDist < leftDist) {
            direction = 'down';
        } else if (leftDist > 0 && leftDist >= upDist) {
            direction = 'left';
        } else {
            direction = 'right';
        }

        if (obj.canMove(direction)) {
            obj.move(direction);
        }
    }

    map.defineObject('attackDrone', {
        'type': 'dynamic',
        'symbol': 'd',
        'color': 'red',
        'onCollision': function (player) {
            player.killedBy('an attack drone');
        },
        'behavior': function (me) {
            moveToward(me, 'player');
        }
    });


    map.placePlayer(1, 1);
    map.placeObject(map.getWidth()-2, 12, 'attackDrone');
    map.placeObject(map.getWidth()-1, 12, 'exit');

    map.placeObject(map.getWidth()-1, 11, 'block');
    map.placeObject(map.getWidth()-2, 11, 'block');
    map.placeObject(map.getWidth()-1, 13, 'block');
    map.placeObject(map.getWidth()-2, 13, 'block');
    map.defineObject('helpDrone', {
        'type': 'dynamic',
        'symbol': 'd',
        'color': 'yellow',
        'onCollision': function (player) {
            player.killedBy('an attack drone');
        },
        'behavior': function (me) {
            moveToward(me, 'attackDrone');
        }
    });
    function maybeCatch(obj, type) {
        var target = obj.findNearest(type);
        var leftDist = obj.getX() - target.x;
        var upDist = obj.getY() - target.y;
        
        var direction;
        if (upDist == 0 && leftDist == 0) {
        	return;
        } if (upDist > 0 && upDist >= leftDist) {
            direction = 'up';
        } else if (upDist < 0 && upDist < leftDist) {
            direction = 'down';
        } else if (leftDist > 0 && leftDist >= upDist) {
            direction = 'left';
        } else {
            direction = 'right';
        }
        
        if (obj.canMove(direction)) {
            obj.move(direction);
        } else {
            map.placeObject(target.x, target.y + 1, 'helpDrone');
            map.placeObject(target.x, target.y - 1, 'helpDrone');
            map.placeObject(target.x + 1, target.y, 'helpDrone');
        }
    }
    map.defineObject('policeDrone', {
        'type': 'dynamic',
        'symbol': 'd',
        'color': 'blue',
        'onCollision': function (player) {
            player.killedBy('an attack drone');
        },
        'behavior': function (me) {
            maybeCatch(me, 'attackDrone');
        }
    });
    map.placeObject(map.getWidth()-20, 12, 'policeDrone');
}

function validateLevel(map) {
    map.validateExactlyXManyObjects(1, 'exit');
}