Vala Tree Objects Files

- Download all files in src folder
- compile :
$ valac --pkg libxml-2.0 --pkg gee-0.6 main.vala objects.vala  abstract_objects.vala  attributes.vala xml_reader.vala
- execute resulted file "main" or "main.exe"

Actually not compatible with gee-0.8 :
>> error: cAbstractObject: some prerequisites (`Gee.Traversable') are not met