Macro try_scan 

macro_rules! try_scan {
    (
        $t:ty
    ) => { ... };
    (
        $p:literal,
        $t:ty
    ) => { ... };
    (
        $($t:ty),*
    ) => { ... };
    (
        $p:literal,
        $($t:ty),*
    ) => { ... };
}