Function play_observed 

pub fn play_observed<R: Sides>(
    rules: &mut R,
    bots_by_side: &mut [(R::Side, &mut dyn Bot<R>)],
    limit: u32,
    observe: impl FnMut(&R, &R::Command, &[R::Event]),
) -> Result<Report<R>, PlayError<R>>
where
    R::Command: Clone,

play, telling observe about every applied command: the game after it, the command and the events it gave. A game’s measures are built this way.