fn main(args: [String])
    println(args[0])
end

int Index<T, I>
    op [](i: I) -> T
end

int Slice<T> : Index<T, ISize>, Iterable<T>
    length: ISize

    def fn iter() -> Iterator<T>
        let mut i = 0
        {
            if i < length then
                i++
                Some(self[i - 1])
            else
                None
            end
        }
    end
end

int Iterator<T>
    fn next() -> Option<T>
end

int Iterable<T>
    fn iter() -> Iterator<T>
end

extern class Array<T> : Index<T, ISize>, Slice<T>
    extern length: ISize
    extern op [](i: ISize) -> T
end

int List<T> : Index<T, ISize>, Slice<T>

end