Function turns 

pub fn turns<R>(
    file: &str,
    initial: R,
    commands: &[R::Command],
) -> Result<ReplayRun, String>
where
    R: TurnRules + Serialize,
    R::Command: Debug,
    R::Event: Debug,
    R::Error: Display,
    R::Outcome: Debug,

Re-runs commands from initial by the rules, hashing the state before them and after each: the run of a turn game’s record file. A refused command changes nothing and says why.