> It’s not easily possible, and I think it would be a bad idea: if every
> service has access to every ‘operating-system’ field, that gives you
> more flexibility, but it’s also much harder to reason about what
> happens, compared to the current extension graph (the NixOS “module”
> system works like that: every service can access every bit of the whole
> configuration, but IMO that makes it quite hard to understand.)

OK, I understand. Just out of curiosity: Why do we have special
operating-system fields like host-name, hosts-file, etc. instead of just
having services like host-name-service-type, hosts-file-service-type,
etc.? Doesn't giving special status to these operating-system fields
complicate things? For example, if we only had a hosts-file-service-type
instead of a hosts-file operating-system field, we wouldn't have the
problem that /etc/hosts could only be created from within
essential-services.

> What could be useful is “self-referential” records, where a field can
> refer to the record it belongs do.  So we’d do:
>
>   (define-record-type* <operating-system>
>     ;; …
>     (services operating-system-services
>               (self-referential? #t) (default essential-services)))
>
> whereby ‘essential-services’ would be passed the <operating-system>
> record somehow.
>
> That needs more thought…

OK, I'll wait.

Thanks!