linea::mat!

macro_rules! mat {
    [$t:ty: $($x0:expr),*] => { ... };
    [$t:ty: $($x0:expr),*; $($($x:expr),*);+] => { ... };
}

Example use: let _: Matrix<usize, U2, U2> = mat![usize: 1, 0; 0, 1];