How can I use ()

[Alex ter Weele]

(Following this conversion on #guix:
https://gnunet.org/bot/log/guix/2018-01-10#T1600427)

I am trying to use the mcron service to run backups. I have written:

(define (backup-home user)
  #~(begin
      (execl
       (string-append #$borg "/bin/borg")
       "create"
       "--stats" "--list" "--verbose"
       "/mnt/borg::{hostname}-{utcnow}"
       (format "/home/%s" #$user))
      ;; TODO: borg prune.
      ))

(define (backup-home-job user)
  #~(job '(next-hour '(18))
         #$(backup-home user)
         #:user #$user))

I would like to run the gexp (backup-home "alex") from the REPL so that
I can verify it works properly. I looked into what the mcron service
itself does with the gexp in order to run it and found that (gnu
shepherd)'s shepherd-configuration-file uses gexp->file.

Based on this, what I think I want to do is something like:

,enter-store-monad
(build (list (gexp->script "test" (backup-home "alex"))))

And then run the resulting script file. However, doing such gives the
error:

ERROR: In procedure string->utf8:
ERROR: In procedure string->utf8: Wrong type argument in position 1 (expecting 
string): #<procedure 327b030 at guix/gexp.scm:1128:2 (state)>

At this point I tried putting a string in what I think is the right
place, once again running in the store monad REPL:

(build "foo" (list (gexp->script "test" (backup-home "alex"))))

But this gives:

ERROR: In procedure length:
ERROR: In procedure length: Wrong type argument in position 1: "foo"

At which point I'm stumped. I'd love to know what I'm doing wrong!

Thanks,
Alex