Solution to level 9 in Untrusted: http://alex.nisnevich.com/untrusted/

untrusted-lvl9-solution.js

/**********************
 * fordingTheRiver.js *
 **********************
 *
 * And there's the river. Fortunately, I was prepared for this.
 * See the raft on the other side?
 *
 * Everything is going according to plan.
 */

function startLevel(map) {
    var raftDirection = 'down';

    map.placePlayer(map.getWidth()-1, map.getHeight()-1);
    var player = map.getPlayer();

    map.defineObject('raft', {
        'type': 'dynamic',
        'symbol': '▓',
        'color': '#420',
        'transport': true, // (prevents player from drowning in water)
        'behavior': function (me) {
            me.move(raftDirection);
        }
    });

    map.defineObject('water', {
        'symbol': '░',
        'color': '#44f',
        'onCollision': function (player) {
            player.killedBy('drowning in deep dark water');
        }
    });

    for (var x = 0; x < map.getWidth(); x++) {
        for (var y = 5; y < 15; y++) {
            map.placeObject(x, y, 'water');
        }
    }

    map.placeObject(20, 5, 'raft');
    map.placeObject(0, 2, 'exit');
    map.placeObject(0, 1, 'block');
    map.placeObject(1, 1, 'block');
    map.placeObject(0, 3, 'block');
    map.placeObject(1, 3, 'block');

    var player = map.getPlayer()
    player.setPhoneCallback(function(){
        var player = map.getPlayer()
        if (player.atLocation(20, 14)) {
            raftDirection = 'up'
        }
        if (player.atLocation(20, 5)) {
            raftDirection = 'down'
        }
    });
    /*
    The conditionals were not strictly necessary, but it doesn't hurt
    to check where I am before doing stuff.
    Twisted Code (sometimes called macks2008 or macks2010) was here
    */

}

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

Not much to this level either. Just make your function phone reverse the raft direction (either anywhere, as some might do, or only if you are on it on the shore)