kefirPlayers.js

function add(a) {return function(b){return a + b}}
function nEq(a) {return function(b){return a !== b}}
function eq(a) {return function(b){return a === b}}
function always(val) {return function(){return val}}
function id(a){return a}

function getPropertyValue(prop){
    var val;
    prop.take(1).onValue(function(_val){val = _val});
    return val;
}

var Player = function(players, movement, initPos){
    var me = {};

    var possibleNewPosition = movement
        .flatMap(function(val){
            return me.position
                .take(1)
                .map(add(val));
        });
    possibleNewPosition.log()

    me.position = possibleNewPosition
        .flatMap(function(posFuture){
            return players
                .take(1)
                .flatMap(function(playersValue){
                    var otherPlayerPositions = Kefir
                        .zip(playersValue
                            .filter(nEq(me))
                            .map(function(player){return player.position.take(1)})
                    )
                    return otherPlayerPositions
                        .map(function(positions){
                            return !positions.some(eq(posFuture));
                        })
                        .filter(id)
                        .map(always(posFuture))
                })
        })
        .toProperty(initPos);
    me.position.log('player:' + initPos);
    return me;
}

var playerJoin = Kefir.bus();
var players = playerJoin
    .scan(function(val, joined){
        return val.concat([joined]);
    }, []);

players.log('players')

var moveA = Kefir.bus();
var moveB = Kefir.bus();

playerJoin.emit(new Player(players, moveA, 0));
playerJoin.emit(new Player(players, moveB, 10));

moveA.emit(4);
moveB.emit(-4);
moveA.emit(1);
moveB.emit(-1);
moveB.emit(-1);
moveB.emit(-1);
moveA.emit(1);
moveA.emit(-1);
moveB.emit(-1);

kefirPlayersHacked.js

function add(a) {return function(b){return a + b}}
function nEq(a) {return function(b){return a !== b}}
function eq(a) {return function(b){return a === b}}
function always(val) {return function(){return val}}
function id(a){return a}

function getPropertyValue(prop){
    var val;
    prop.take(1).onValue(function(_val){val = _val});
    return val;
}

var Player = function(players, movement, initPos){
    var me = {};

    var possibleNewPosition = movement
        .map(function(val){
            return getPropertyValue(me.position) + val;
        });
    possibleNewPosition.log()

    me.position = possibleNewPosition
        .filter(function(posFuture){
            var playersValue = getPropertyValue(players);
            var positions = playersValue
                .filter(nEq(me))
                .map(function(player){return getPropertyValue(player.position)})
            return !positions.some(eq(posFuture));
        })
        .toProperty(initPos);
    me.position.log('player:' + initPos);
    return me;
}

var playerJoin = Kefir.bus();
var players = playerJoin
    .scan(function(val, joined){
        return val.concat([joined]);
    }, []);

players.log('players')

var moveA = Kefir.bus();
var moveB = Kefir.bus();

playerJoin.emit(new Player(players, moveA, 0));
playerJoin.emit(new Player(players, moveB, 10));

moveA.emit(4);
moveB.emit(-4);
moveA.emit(1);
moveB.emit(-1);
moveB.emit(-1);
moveB.emit(-1);
moveA.emit(1);
moveA.emit(-1);
moveB.emit(-1);