Macro pnmixerlib::try_wr

macro_rules! try_wr {
    ($expr:expr, $ret:expr) => { ... };
    ($expr:expr, $ret:expr, $fmt:expr) => { ... };
    ($expr:expr, $ret:expr, $fmt:expr, $($arg:tt)+) => { ... };
}

Try to unwrap a Result<T, E>. If there is a value T, yield it, otherwise print a warning and return from the function with the given value.