How do you write input based yield?

Question

I'm trying to implement a turn queue. I want to right click, have one child node do something, right click again, and have the other child node do something. How do I do that? This is what I have so far. Parent node:

 func _ready():
    set_process_input(true)
    active_player = self.get_child(0)

func _input(event):
    if event.is_action_pressed("right_click"):
        play_turn()

func play_turn():
    #yield(active_player.play_turn(), "completed") 
    var new_index : int = (active_player.get_index() + 1) % get_child_count()
    active_player = get_child(new_index)

Child node:

func _ready():
        play_turn()

func play_turn():
        yield(TurnQueue.play_turn(), "completed")

I'm getting and error in the child node: "Non-static function "play_turn" can only be called from an instance. The only guide I could find on turn queues doesn't explain player input directed turn changes.

Comments

I got it to work with signals and taking out the yield.