YAML problem, possibly?

I obtained a largish lump of shallow XML, succcessfully read it with
REXML, and then tried to YAML dump it.

The files I obtained were
http://prdownloads.sourceforge.net/annabot/AnnaAIML-.7.0.zip?download

which is AIML based so the maximum depth of the XML is
<aiml>
   <topic>
     <category>
       <template>
         <srai>
           <srai>
           </srai>
         </srai>
     </category>
   <topic>
<aiml>

though there may be many categories, as in file anna_brain/D.aiml .

The results I get are these:


E:\Downloads\AnnaAIML-.7.0\anna_brain>xml_to_yaml.rb
<aiml> ... </>
c:/ruby/lib/ruby/1.8/yaml/rubytypes.rb:287:in `is_complex_yaml?': stack level t
o deep (SystemStackError)
         from c:/ruby/lib/ruby/1.8/yaml/rubytypes.rb:300:in `to_yaml'
         from c:/ruby/lib/ruby/1.8/yaml/baseemitter.rb:177:in `map'
         from c:/ruby/lib/ruby/1.8/yaml/baseemitter.rb:172:in `each'
         from c:/ruby/lib/ruby/1.8/yaml/baseemitter.rb:172:in `map'
         from c:/ruby/lib/ruby/1.8/yaml/rubytypes.rb:25:in `to_yaml'
         from c:/ruby/lib/ruby/1.8/yaml/rubytypes.rb:24:in `call'
         from c:/ruby/lib/ruby/1.8/yaml.rb:335:in `quick_emit'
         from c:/ruby/lib/ruby/1.8/yaml/rubytypes.rb:24:in `to_yaml'
          ... 1120 levels...
         from c:/ruby/lib/ruby/1.8/yaml.rb:103:in `dump'
         from E:/Downloads/AnnaAIML-.7.0/anna_brain/xml_to_yaml.rb:10
         from E:/Downloads/AnnaAIML-.7.0/anna_brain/xml_to_yaml.rb:9:in `open'
         from E:/Downloads/AnnaAIML-.7.0/anna_brain/xml_to_yaml.rb:9

E:\Downloads\AnnaAIML-.7.0\anna_brain>ruby --version
ruby 1.8.2 (2004-07-29) [i386-mswin32]

E:\Downloads\AnnaAIML-.7.0\anna_brain>type xml_to_yaml.rb
require "rexml/document"
require "yaml"

doc = nil
open("I.aiml", "r") {|input|
   doc=REXML::Document.new(input)
}
p doc.root()
open("I.yaml","w") {|output|
     output.print YAML.dump(doc.root())
}


E:\Downloads\AnnaAIML-.7.0\anna_brain>`o


It is my belief that for an XML file so shallow, YAML should not
recurse so deeply when dumping the REXML document.  Is there a
reason why I am wrong? Should I be doing this differently?


         Hugh