sub flatten {
    my ($LoL) = @_;
    my @flat;
    for my $arr (@$LoL) {
        if ( ref $arr ) {
            push(@flat,flatten($arr));
        }
        else {
            push(@flat,$arr);
        }
    }
    return @flat;
}

my @arr = ([1,2],[3,4,[5,6]],7);
my @list = flatten(\@arr);
print "@list\n";