pub fn main(world: World) -> Void raises {
    var out: [8]u8 = [0_u8; 8]
    let joined: Maybe<Span<u8>> = std.str.concat(out, "zero", "lang")
    if joined.has && std.mem.eql(joined.value, "zerolang") {
        check world.out.write("string concatenation ok\n")
    }
}