/// clickType declared elsewhere in code.
checkBoxFast.addEventListener(clickType, goFast("yes"));

function goFast(evt:Event=null,myVar:String)
{
trace(myVar);
}

checkBoxFast.addEventListener(clickType, function(e:Event):void{goFast("yes")});

function goFast(myVar:String)
{
    trace(myVar);
}

public class MyEvent extends Event {
    public var myVar:String;

    public function MyEventHistoryEvent(type:String, bubbles:Boolean=false, cancelable:Boolean=false) {
        super(type, bubbles, cancelable);
    }
}

var event:MyEvent = new MyEvent("eventType");
event.myVar = "yes";

dispatchEvent(event);

checkBoxFast.addEventListener("eventType", eventHandler);

protected function eventHandler(event:MyEvent):void {
trace(event.myVar);
}

public function test() {

        var myVar : String = "some value";
        addEventListener(MouseEvent.CLICK, onClick);


        function(e:Event){
            trace(myVar);
        }

    }