Existential quantification versus explicit types
Can you make Player a datatype instead of a typeclass? The datatype can have exactly the same methods but with the first argument elided. Make Player an instance of Show, and voilá, data Players = Players Player Player Player. One implications is that a bot and a human player are now both just values of the same type, Player. Thus the chooseCard, chooseCardOpen and onCardPlayed of a bot can yield a human with a hand and cards on the table mid-game, and vice versa. I'd love to have the freedom to have a bot play the first few rounds for me, yield to me when the game starts going, and play out the last couple of rounds when I feel victory is secure! And as you note, you already opted to give every player type MonadIO, anyway, so these types are not really looser.