pub fn main(world: World) -> Void raises {
    let text: String = "abcdef"
    let start: usize = 1
    let end: usize = 4
    let middle: Span<u8> = text[start..end]
    if std.mem.len(middle) == 3 {
        check world.out.write("dynamic slice ok\n")
    }
}