Macro debug

macro_rules! debug {
    () => { ... };
    ($($val: expr),+,) => { ... };
    ($($lab: expr => $val: expr),+,) => { ... };
    ($valf: expr $(, $val: expr)*) => { ... };
    ($labf: expr => $valf: expr $(, $lab: expr => $val: expr)*) => { ... };
}