Macro array 

macro_rules! array {
    (@accum (0, $($_es:expr),*) -> ($($body:tt)*)) => { ... };
    (@accum (1, $($es:expr),*) -> ($($body:tt)*)) => { ... };
    (@accum (2, $($es:expr),*) -> ($($body:tt)*)) => { ... };
    (@accum (3, $($es:expr),*) -> ($($body:tt)*)) => { ... };
    (@accum (4, $($es:expr),*) -> ($($body:tt)*)) => { ... };
    (@accum (5, $($es:expr),*) -> ($($body:tt)*)) => { ... };
    (@accum (6, $($es:expr),*) -> ($($body:tt)*)) => { ... };
    (@accum (7, $($es:expr),*) -> ($($body:tt)*)) => { ... };
    (@accum (8, $($es:expr),*) -> ($($body:tt)*)) => { ... };
    (@as_expr $e:expr) => { ... };
    [$e:expr; $n:tt] => { ... };
}

Allow the creation of compile-time arrays of state up to 8 elements long without needing the Copy trait to be implemented.

Derived from: https://danielkeep.github.io/tlborm/book/pat-push-down-accumulation.html