How to add a variable with a list of services into another list of services?

[Oleander via]

Hi,
I'm trying to write a module with this list of services:

(define bar
(list
(service foo1-service-type)
(service foo2-service-type)))

How do I add the "bar" variable into the "(services..." declaration which 
already contains a list of services?

I've tried without success:

(services
(append
(list ...)
bar
(modify-services %base-services...

Thanks in advance!