Function single_op_unary 

pub fn single_op_unary<D1, D2, F, T, G>(
    name: &str,
    in_stream: &Stream<G, D1>,
    op: F,
) -> Stream<G, D2>
where
    D1: Data + Debug + ExchangeData,
    D2: Data + Debug,
    F: Fn(D1) -> D2 + 'static,
    T: Timestamp + Copy,
    G: Scope<Timestamp = T>,