Nested gexps in mcron job definitions

[Yulran <yulran@posteo.net>]

Hi guix,

I'm having trouble with nesting g-expressions when defining a mcron job. I want the job to run the same "mastodon-archive" commands for several accounts, so I define a list of accounts and use 'map' to build the complete command. This works well when there are only strings involved, but I can't make it work with gexps.

Here's a simplified example with only strings:

--8<---------------cut here---------------start------------->8---
(define succeeding-job
  (let* ((accounts '("account1" "account2"))
         (cmd (apply string-append
                     (map
                      (lambda (acct)
                        (string-append
                         "mastodon-archive archive " acct "; "))
                      accounts))))
    #~(job '(next-second (range 1 61 10))
           (lambda ()
             (system (string-append "echo '" #$cmd "'")))
           "mastodon-archive")))
--8<---------------cut here---------------end--------------->8---

The job succeeds and the mcron log prints as expected "mastodon-archive archive account1; mastodon-archive archive account2;". Now to use the full path to the mastodon-archive binary, cmd must be a gexp:

--8<---------------cut here---------------start------------->8---
(define failing-job
  (let* ((accounts '("account1" "account2"))
         (cmd #~(apply string-append
                       (map
                        (lambda (acct)
                          (string-append
                           #$mastodon-archive "/bin/mastodon-archive archive " acct "; "))
                        #$accounts))))
    #~(job '(next-second (range 1 61 10))
           (lambda ()
             (system (string-append "echo '" #$cmd "'")))
           "mastodon-archive")))
--8<---------------cut here---------------end--------------->8---

The home configuration builds fine, but the mcron job fails with the error: (wrong-type-arg #f Wrong type to apply: ~S (account1) (account1))

I played around with gexp-ing the string-append in the lambda, ungexp-ing acct, and trying every other combination of gexp/ungexp I could think of, but I could only make it worse.

Any idea what I'm doing wrong?