Add an xfce session to SLiM login menu

[白い熊＠相撲道]

Hello:

I'd like to reconfigure the system, so that it offers ratpoison and xfce 
as session types in SLiM.

In sysconfig.scm I currently have:

(services (cons* (slim-service #:sessions (list 
%ratpoison-session-type))
...

How do I add xfce there?

Also, I need to probably add a (packages... section with xfce. Could 
someone give me the proper line for this?

Anything else needed?
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白い熊＠相撲道