sub gen_merger {
    my ($list, $fetch, $compare, $finish) = @_;
    my @item = map $fetch->($_), @$list;
    
    my $done;
    return sub {
        return $finish if $done;        
        my $idx  = first {$item[$_] ne $finish} 0 .. $#item;
        my $next = $item[$idx];
        for ($idx + 1 .. $#item) {
            next if $item[$_] eq $finish;
            my $result = $compare->($next, $item[$_]);
            #$next = $item[$_] if $result == 1;
            # Need to keep track of which one we use not just value
            ($idx, $next) = ($_, $item[$_]) if $result == 1;
        }
        $item[$idx] = $fetch->($list->[$idx]);
        #$done = 1 if ! first {$item[$_] ne $finish} $idx .. $#item;
        # First element of array is 0 so use defined instead of truth
        $done = 1 if ! defined first {$item[$_] ne $finish} $idx .. $#item;
        return $next;
    };
}