pub fn main(world: World) -> Void raises {
    let left: [2]i32 = [1, 2]
    let right: [3]i32 = [3, 4, 5]
    var both: [5]i32 = [0; 5]
    var len: usize = 0
    len = std.collections.append(both, len, left)
    len = std.collections.append(both, len, right)
    if len == 5 && both[0] == 1 && both[4] == 5 {
        check world.out.write("array concatenation ok\n")
    }
}