macro_rules! impl_rolling_hasher {
(@inner $T:ident, $R:ty, [$($i:tt)*] [$($s:tt)*] [$a:tt $($tt:tt)*] [$k:tt $($j:tt)*]) => { ... };
(@inner $T:ident, $R:ty, [$($i:tt)+] [$($s:tt)+] [] [$len:tt $($j:tt)*]) => { ... };
($T:ident, $R:ty, [$($tt:tt)+]) => { ... };
}