Actionscript

//variables
var allDown:Boolean=false
if(rightDown=true && leftDown==true){
    allDown=true
}
var allUp:Boolean=true
if(rightDown=false && leftDown==false){
    allUp=true
}
var rightDown:Boolean=false
var leftDown:Boolean=false
var playerXSpeed:int=0
var playerYSpeed:int=0
var maxPositiveSpeed:int=10
var maxNegativeSpeed:int=maxPositiveSpeed-maxPositiveSpeed*2
//event listeners
stage.addEventListener(Event.ENTER_FRAME, updateGame);
addEventListener(KeyboardEvent.KEY_DOWN, keyHandler);
addEventListener(KeyboardEvent.KEY_UP, keyHandler);
//functions
function updateGame(event){
    movePlayer();
    updateSpeed();
}
function movePlayer(){
    player.x+=playerXSpeed
}
function updateSpeed(){
    if(rightDown==true && playerXSpeed>maxPositiveSpeed){
        playerXSpeed+=1
    }
    if(leftDown==true && playerXSpeed>maxNegativeSpeed){
        playerXSpeed-=1
}
    if(allUp==true && playerXSpeed<0){
        playerXSpeed-=1
    }
    if(allUp==true && playerXSpeed>0){
        playerXSpeed+=1
    }
}
function keyHandler(event){
    if(event.keyCode==68 || event.keyCode==39){
        if(rightDown==true){
            rightDown=false
        }
        else{
            rightDown=true
        }
    }
    if(event.keyCode==65 || event.keyCode==37){
        if(leftDown==true){
            leftDown=false
        }
        else{
            leftDown=true
        }
    }
}