my $finish   = 'A val that is guaranteed not to be present in any list';
my @list     = (\@arr1, \@arr2, \@arr3, \@arr4, \@arr5);
my $fetch    = sub {
    my $item = shift @_;
    return $finish if ! $@item;
    return shift $@item;
};
my $compare  = sub {
    my ($item1, $item2) = @_;
    return uc($item1) cmp uc($item2);
}
my $next = gen_merger(\@list, $fetch, $compare, $finish);
while (1) {
    my $item = $next->();
    last if defined $item && $item eq $finish;
    print "$item\n";
}