Installing system with packages, sysconfig.scm syntax

["白い熊 @相撲道" <guix-devel_gnu.org@sumou.com>]

I'm trying to understand the sysconfig.scm syntax to specify when clean installing the system or running “guix system reconfigure”. 

In the manual I've seen the example with Emacs. But I don't understand why there's: 

(use-modules (gnu)
             (gnu packages emacs)

and then in the operating-system section

(packages (cons emacs %base-packages))

Let's just say I want to reconfigure the system with packages emacs, mc, xmodmap, and xterm installed for user joe. What do I put in the sysconfig.scm? I've tried many combinations, but can't accomplish this simple task. 

I understand I can install the system with a working sysconfig.scm and then install the packages manually via “guix package -i” but I think they all can be defined in sysconfig.scm, just can't figure out how, even though I'm trying to get hints in the manual. Or am I wrong in this? 

Also, when installing from the USB, after booting the USB, can I “guix pull” and then install the system? Or do I have to first install, then boot it, then “guix pull”, meaning I couldn't maybe put all package definitions in the install sysconfig.scm, as the packages might not be available before “guix pull”? 


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白い熊 @相撲道