my @tokens = get_tokens $string;

my sub parse_list {
    my @list;
    while (my $token = shift @tokens) {
        if ($token eq '(') {
            push @list, __SUB__->();
        } elsif ($token eq ')') {
            return \@list;
        } else {
            push @list, $token;
        }
    }
    return \@list;
}

my $list = parse_list;