Function this_or_that_picks_first 

fn this_or_that_picks_first(
    err_a: Option<Error>,
    err_b: Option<Error>,
    args: &mut State,
    args_a: &mut State,
    args_b: &mut State,
) -> Result<bool, Error>

Given two possible errors along with to sets of arguments produce a new error or an instruction to pick between two answers. Updates arguments state to match the results