macro_rules! impl_zero_one {
($({$(<$T:ident: $Bound:ident>)? $Trait:ident $method:ident $($t:ty)*, $e:expr})*) => { ... };
(@impl [<$T:ident: $Bound:ident>] $Trait:ident $method:ident [$($t:ty)*], $e:expr) => { ... };
(@impl [] $Trait:ident $method:ident [$($t:ty)*], $e:expr) => { ... };
}