XML::LibXML::Reader source specification error

[perl]

I tried to use LibXML .. when i never to the correct libXML read file
... when i tried to use the LWP download which is an XML .. how to use
it please help  me ...

/use LWP::UserAgent;
my $ua = LWP::UserAgent->new;
my $response =
$ua->get("http://www.perlmonks.org/?displaytype=xml;node_id=3989";);
 if ($response->is_success) {
     my $string = $response->content;  # or whatever
 }
 else {
     die $response->status_line;
 }
    use XML::LibXML::Reader;
  my $reader = new XML::LibXML::Reader( string => $string )
         or die "cannot read file.xml\n";
  while ($reader->read) {
    processNode($reader);
  }

  sub processNode {
      $reader = shift;
      printf "%d %d %s %d\n", ($reader->depth,
                               $reader->nodeType,
                               $reader->name,
                               $reader->isEmptyElement);
}/