How I can create a player instance?

It has been successful! It is what I want to do!!

    var FoundValue : int = 0
    var FoundPlayer : ?player = false
    for (Key->Value: PlayerMap):
        if (Value >= FoundValue):
            set FoundValue = Value
            set FoundPlayer = option{Key}
    if (Player := FoundPlayer?):
        EndDevice.Activate(Player)

But, I have a question. If I want to use the function as follow:

    CheckEndGame()  : void=
           if (Player := GetLowestValuedPlayer()?):

I have the following error:

This invocation calls a function that has the ‘no_rollback’ effect, which is not allowed by its context.