Macro immutable_seq::build_digit

macro_rules! build_digit {
    ($($f0: expr, $f1: expr, $f2: expr),+) => { ... };
    ($e0: expr, $e1: expr $(, $f0: expr, $f1: expr, $f2: expr)*) => { ... };
    ($e0: expr, $e1: expr, $e2: expr, $e3: expr $(, $f0: expr, $f1: expr, $f2: expr)*) => { ... };
}