Sent with Proton Mail secure email.
On Monday, August 11th, 2025 at 8:27 AM, Carlo Zancanaro
<[email protected]> wrote:
> Hi Alexander,
>
> Apologies for the second email, but I forgot to Cc the list the first
> time. Whoops!
>
> On Tue, Aug 05 2025, Alexander Prähauser via wrote:
>
> > The shepherd-manual specifies in the make-timer-constructor that
> >
> > "ACTION
> > may be either a command (returned by ‘command’) or a thunk; in the
> > latter case, the thunk must be suspendable or it could block the
> > whole shepherd process."
> >
> > but this is the only place in that manual that the word "thunk"
> > appears, I don't know what it is.
>
>
> A thunk is just a procedure that takes zero arguments. The term is
> defined in the Scheme standard (e.g. section 1.3.5 of R7RS), so I don't
> think it's specifically defined in the Guix or Shepherd manuals.
>
> Looking at the shepherd-timer helper in Guix, I don't think you can use
> a thunk, though. It always uses "command" to wrap the gexp given to it,
> so you'll have to use the lower-level shepherd-service primitives to do
> it.
>
> > So is it even possible to have timers that run Guile-functions, and if
> > so, what is the correct syntax for that?
>
>
> Something like this (untested, but taken mostly from the example in the
> manual in "(guix) Scheduled Job Execution") might work:
>
> --8<---------------cut here---------------start------------->8---
>
> (shepherd-service
> (provision '(battery-notifier))
> (requirement '(user-processes))
> (modules '((shepherd service timer)))
> (start #~(make-timer-constructor
> (cron-string->calendar-event "0,10,20,30,40,50 * * * *")
>
> (lambda ()
> ;; You'll need to make sure this is available in the
> ;; gexp, possibly using with-imported-modules and
> ;; use-modules - see "(guix) G-Expressions" in the
> ;; manual for more details.
> (ahp-notify-when-battery-low))
> #:wait-for-termination? #t))
> (stop #~(make-timer-destructor))
> (documentation "Periodically check battery status.")
> (actions (list shepherd-trigger-action)))
> --8<---------------cut here---------------end--------------->8---
>
> > It would be really nice if an example of that were in the
> > manual. There is a more involved example for mcron, but I'm not sure
> > if it also applies to shepherd-timers and since I have to reboot each
> > time this doesn't work I'm reluctant to try.
>
>
> Restarting the relevant service (either the timer service, or mcron)
> after a system reconfigure should load the new schedule. This should
> make experimenting much cheaper. 🙂
>
> Carlo
Thanks Carlo! I'll still have to figure out how to import the funciton but the
timer seems t seems to work!
Alex
