I've found this example: https://github.com/alezost/guix-config/blob/master/system-config/os-main.scm <https://github.com/alezost/guix-config/blob/master/system-config/os-main.scm>

and have typed this for disable pc speaker:


(define %redundant-linux-modules '("pcspkr" "snd_pcsp"))

(operating system
...
 (kernel-arguments
     (list (string-append "modprobe.blacklist="
                          (apply comma-separated
    %redundant-linux-modules)))))


# guix system reconfigure /etc/config.scm
/etc/config.scm:97:26: error: comma-separated: unbound variable
hint: Did you forget a `use-modules' form?

I've downloaded Guix git and found this word but no anywhere declaration of comma-separated function:

$ git clone https://git.savannah.gnu.org/git/guix.git/ <https://git.savannah.gnu.org/git/guix.git/>
$ grep -rl comma-sep .
./etc/completion/fish/guix.fish
./tests/cran.scm
./tests/ui.scm
./doc/guix.texi
./doc/guix.fr.texi
./doc/guix.de.texi
./po/packages/da.po
./po/packages/de.po
./po/packages/es.po
./po/packages/zh_CN.po
./po/packages/fr.po
./po/packages/pl.po
./po/packages/hu.po
./po/doc/guix-manual.fr.po
./po/doc/guix-manual.pot
./po/doc/guix-manual.de.po
./po/guix/pt_BR.po
./po/guix/da.po
./po/guix/sv.po
./po/guix/de.po
./po/guix/es.po
./po/guix/zh_CN.po
./po/guix/fr.po
./po/guix/pl.po
./gnu/packages/music.scm
./gnu/packages/bootstrap/x86_64-linux/xz
./gnu/packages/bootstrap/aarch64-linux/xz
./gnu/packages/bootstrap/mips64el-linux/xz
./gnu/packages/bootstrap/i686-linux/xz
./gnu/packages/bootstrap/armhf-linux/xz
./gnu/packages/perl.scm
./gnu/packages/textutils.scm
./gnu/services/mail.scm
./gnu/services/kerberos.scm
./gnu/build/accounts.scm
./guix/scripts/gc.scm
./guix/ui.scm
./guix/import/cran.scm


How to tell guix how to use comma-separated function??
Mentioned github page has no any use-modules string that can help.