def flatten(l):
    """
    Flattens a hierarchy of nested lists into a single list containing all elements in order

    :param l: list of arbitrary types and lists
    :returns: list of arbitrary types
    """
    l = list(l)
    i = 0
    while i < len(l):
        while isinstance(l[i], list):
            if not l[i]:
                l.pop(i)
                i -= 1
                break
            else:
                l[i:i + 1] = l[i]
        i += 1
    return l
