Splitting up the operating-system configuration

[Daniel Schäfer]

Hi,

when my system configuration file grows large, I want to split it up 
into multiple files.
For example, I'd like to have a set of basic configurations for all of 
my systems, one for just the laptops, one for all systems with a GUI and 
so on.

On NixOS I have been doing this by using `imports = [ base.nix 
laptop.nix guix.nix ];`,where each imported file looks like just another 
system configuration and Nix merges them all together.
Is there something like this in Guix, which can merge multiple configs 
together?

My first try was to use modules and define variables. This could be a 
list called `my-gui-packages` that I then use in the machine specific 
configuration file and add it to the `operating-system`.
"Including" such a configuration layer, however, requires much change to 
the machine configuration file that has the `use-module` statement.

What I'm doing now, is to define services in separate modules and 
include them in the machine specific `operating-system`.
With this approach I define my own service that can override other 
services, such as adding packages to the global environment 
(profile-service-type),
adding my user (account-service-type), adding config files to /etc 
(etc-service-type).

But can I do everything by defining a service? Can I change the values 
of `operating-system`, such as `keyboard-layout`, `kernel-arguments`?
Adding to `services` is equivalent to adding a `service-extension` in my 
custom service, right?

Kind of a side question: Can I set a global environment variable, such 
as $EDITOR in my config?

Thanks,
Daniel