Function configure 

fn configure<F>(socket_path: &str, plan: F) -> Result<usize, String>
where
    F: Fn(&[Screen]) -> Result<Vec<(ZwlrOutputHeadV1, Plan)>, String>,

Apply plan to the compositor’s enabled screens, retrying while the compositor cancels. plan receives them in screen order and answers with the heads to change; heads it leaves out keep their configuration. It is called once per attempt, against the screens of that attempt. 0 = the compositor manages no outputs, or the plan asked for nothing.