fn write_first(bytes: mutref<MutSpan<u8>>, value: u8) -> Void {
    bytes[0] = value
}

fn read_first(bytes: ref<MutSpan<u8>>) -> u8 {
    return bytes[0]
}

pub fn main(world: World) -> Void raises {
    var backing: [3]u8 = [0, 0, 0]
    var bytes: MutSpan<u8> = backing
    write_first(&mut bytes, 65_u8)
    if read_first(&bytes) == 65_u8 && backing[0] == 65_u8 {
        check world.out.write("mutref indexed lvalues ok\n")
    } else {
        check world.out.write("mutref indexed lvalues failed\n")
    }
}