macro_rules! chain {
    { $name:ident = $e:expr, $($lhs:expr => $rhs:expr),* } => {{
        let mut $name = $e;

        loop {
            match true {
                $(_ if $lhs => { $name = $rhs })*,
                _ => { break },
            }
        }

        $name
    }}
}

macro_rules! branch {
    { $name:ident = $e:expr, $($lhs:expr => $rhs:expr),* } => {{
        let mut $name = $e;

        match true {
                $(_ if $lhs => { $name = $rhs })*,
                _ => { },
        }

        $name
    }}

}

fn main() {
    let x = chain! {
        x = 5,
        x == 6  => x * 2,
        x == 5  => x + 1,
        x == 7  => 0
    };

    assert!(x == 12);

    let y = branch! {
        y = 5,
        y == 6 => y * 2,
        y == 5 => y + 1,
        y == 7 => 0
    };

    assert!(y == 6);
}