[library(archive)] How to correctly use?

Hi Prologgers,

I'm trying to use `library(archive)` and would like to be able to
reproduce behavior I can also achieve with a GNU tool such as gunzip.

Archive file size in gunzip:
~~~{.sh}
$ gunzip -l elezione.rdf.gz
         compressed        uncompressed  ratio uncompressed_name
             330649             6879677  95.2% elezione.rdf
~~~

Trying to receive the same information using `library(archive)`:
~~~{.pl}
?- archive_open('elezione.rdf.gz', Archive,
[format(all),format(raw)]), archive_next_header(Archive, Path),
archive_header_property(Archive, size(Size)).
Archive = <archive>(0x8ac480),
Path = data,
Size = 0.
~~~

Any ideas and/or sharing of experience with this library by others is
very much appreciated.

---
Cheers!,
Wouter.

E-mail: [email protected]
WWW: www.wouterbeek.com
Tel.: 0647674624