I am grooving on XML::Twig, but I can't seem to master the usage of the replace method. In short, I have a series of rules defined in XML, and I want "duplicate" rules to overwrite the first instance of the rule, in a way that maintains the ordering of the rules. XML::Twig's 'replace' method isn't quite working as I thought it would. My test XML file: 
<?xml version="1.0" ?>
<tcf>
  <tweak name = "T1">
    <description>D1</description>
  </tweak>
  <tweak name = "T2">
    <description>D2</description>
  </tweak>
  <tweak name = "T3">
    <description>D3</description>
  </tweak>
  <tweak name = "T2">
    <description>This should overwrite the old T2.</description>
  </tweak>
</tcf>

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My code (trimmed way down to just show the problem): 
#!/usr/bin/perl

use strict;
use XML::Twig;

# As each tweak tag is processed, this subroutine is called.  Here we 
+will
# see if any previous tweak tag had the same name element.  If so, we 
+will
# overwrite the previous tweak tag with this new tweak tag's contents,
+ then
# delete the new tweak tag.
sub pruner {
    my $this_tweak = $_;
    my $tweakname = $this_tweak->att('name');
    my $exp = "/tcf/tweak[\@name=\"$tweakname\"]";
    my @matches = $this_tweak->get_xpath($exp);
    
    print "TWEAK: ";
    $this_tweak->print;
    print " (Found $#matches other parsed tweaks with the same name)\n
+";

    # If the tweak's name is found elsewhere, replace the first
    # instance with the latest one, then delete the latest one.
    if ($#matches == 1) {
    print "\tReplacing\n\t\t";
    @matches[0]->print;
    print "\n\twith\n\t\t";
    $this_tweak->print;
    print "\n";
    $this_tweak->replace(@matches[0]);
    }
}

my $twig = XML::Twig->new(expand_external_ents => 1,
              twig_handlers => { 'tweak' => \&pruner }
    );

$twig->parsefile("/home/igo/StormLogic/MythiC/Tweaker/test5.tcf");

print "TWIG:\n";
$twig->print;
print "\n";

[download]
When I run that code on that XML file, here is the output: 
$ ./twig_replace_test.pl 
TWEAK: <tweak name="T1"><description>D1</description></tweak> (Found 0
+ other parsed tweaks with the same name)
TWEAK: <tweak name="T2"><description>D2</description></tweak> (Found 0
+ other parsed tweaks with the same name)
TWEAK: <tweak name="T3"><description>D3</description></tweak> (Found 0
+ other parsed tweaks with the same name)
TWEAK: <tweak name="T2"><description>This should overwrite the old T2.
+</description></tweak> (Found 1 other parsed tweaks with the same nam
+e)
    Replacing
        <tweak name="T2"><description>D2</description></tweak>
    with
        <tweak name="T2"><description>This should overwrite the old T2
+.</description></tweak>
TWIG:

[download]
It should print the Twig at the end, but it gets stuck. Am I abusing the replace method and/or putting the Twig into a broken state? This is one particular instance of the problems I've had trying this sort of thing. I wanted to understand what I'm doing wrong with this tiny example first so I can tackle the larger case on my own. Thanks!

In reply to XML::Twig replace method behaving counter-intuitively by Human

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