Macro holmes::typed_unpack

macro_rules! typed_unpack {
    ($val:expr, [$typ:tt]) => { ... };
    ($val:expr, ($($typ:tt),*)) => { ... };
    ($val:expr, $name:ident) => { ... };
}

Given a value and a type it is believed to be, unpack it to the greatest extent possible (e.g. unpack through tupling and lists)