bug#48974: A possible shepherd bug (it's very minor)

[Joshua Branson via Bug reports for GNU Guix <bug-guix@gnu.org>]

Leo Prikler <leo.prikler@student.tugraz.at> writes:

> Hi,
>
> Am Freitag, den 25.06.2021, 05:31 -0400 schrieb Joshua Branson:
>> Leo Prikler <leo.prikler@student.tugraz.at> writes:
>>
>> > Hi,
>> >
>> > Am Samstag, den 12.06.2021, 20:09 +0000 schrieb jbranso@dismail.de:
>> > > June 12, 2021 3:39 PM, "Leo Prikler" <
>> > > leo.prikler@student.tugraz.at>
>> > > wrote:
>> > >
>> > > > Am Samstag, den 12.06.2021, 09:26 -0400 schrieb Joshua Branson:
>> > > >
>> > > > > Hello!
>> > > > >
>> > > I'll tell you what, why don't we leave this "bug" open for a
>> > > week...I'll try to write
>> > > the code that does what I want, and I'll email the answer.
>> > >
>> > > Then I'll edit the manual to provide an example!
>> Well, it's been about a week. Here is my current code that doesn't
>> work.
>> haha.
>>
>> #+BEGIN_SRC scheme
>> (define %my-desktop-services
>>   (modify-services %desktop-services ;;end of remove services
>>     (mingetty-service-type config =>
>>                            (mingetty-configuration
>>                             (inherit config)
>>                             ;; ERROR at the NEXT LINE
>>                             (auto-login-to-tty-3 config)
>>                             ))))
>>
>> (define (auto-login-to-tty-3 config)
>>   (if (string=? "3" (mingetty-configuration-tty config))
>>       '(auto-login "joshua")
>>       '(auto-login #f)))
>> #+END_SRC
>>
>> It obviously doesn't work because I am treating modify-services as if
>> it were a procedure.  In fact, it is a macro.  :)
> That's not the issue here, the issue is that you're treating mingetty-
> configuration as… I'm not really sure what exactly, when it is in fact
> a record constructor.

Oh!!!! Light bulb!  I knew that!  I've made quite a few record
constructors for endlessh and my almost complete sway service:

http://issues.guix.gnu.org/39136
https://notabug.org/jbranso/guix-config/src/master/sway-service.scm

>
> Try the following:
>
> #+BEGIN_SRC scheme
> (define (auto-login-to-tty tty user)
>   ;; TODO: you might want to implement this as match-lambda instead

I will try that!

>   (lambda (config)
>     (if (string=? tty (mingetty-configuration-tty mingetty-config))
>         (mingetty-configuration
>           (inherit config)
>           (auto-login user))
>         config)))
>
> (define %my-desktop-services
>   (modify-services %desktop-services
>
> (mingetty-service-type config =>
>                           (auto-login-
> to-tty "3" "joshua"))))
> #+END_SRC
>

Hmmm.  Is that (define (auto-login-to-tty tty user) ...) a closure?  I
wonder why you need that lambda inside of it...Probably to pass the
config variable into the function...hmmm.  I still don't understand why
it is necessary.  I'll think about that a bit later on.

>
>> #+BEGIN_SRC scheme
>> (define (auto-login-to-tty-3 mingetty-service)
>>   (if (string=? "3" (mingetty-configuration-tty config))
>>       '(mingetty-configuration
>>          (auto-login "joshua")
>>          (tty "3"))
>>       mingetty-service))
> Don't quote mingetty-configuration et al.  They're first-class syntax,
> not just weird lists.

Yeah that's true.  I do actually like (guix records)!  I feel like that
file should be upstreamed into guile!

>
>> (define (my-modify-%desktop-services-to-auto-login-on-tty-3 %desktop-
>> services)
>>    ;; to be written
>>    ;; though I think fold, or map, may be useful functions here.
>>
>>    ;;somehow I will use this function...
>>     (auto-login-to-tty-3 mingetty-service)
>> )
>>
>> (define %my-desktop-services
>>         (my-modify-%desktop-services-to-auto-login-on-tty-3 %desktop-
>> services))
> I don't think you need to implement modify-services on your own, rather
> just use the existing thing in the "correct" way – i.e. adhering to the
> expectations given by the already existing procedure (or macro).

Thanks again!  The current code doesn't quite work for me yet.  I'll try
using match-lambda to define it.  I'll post again when I have a free
moment.  When i get it working, I'll send a patch to the manual via
guix-patches and CC you.  Is that ok?  Or would you rather that
documentation be in the cookbook?

>> #+END_SRC
> Regards,
> Leo
>

--
Joshua Branson (joshuaBPMan in #guix)
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