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[PATCH] doc: Document the use of `program-file' for mcron jobs. |
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Thu, 01 Aug 2019 09:27:45 +0900 |
Hello!
This follows up to my second post under the thread at
(https://lists.gnu.org/archive/html/help-guix/2019-07/msg00180.html).
It aims to shed some light on (more) complex mcron job Guile scripting
with the aid of Guix features (such as program-file).
0001-doc-Document-the-use-of-program-file-for-mcron-jobs.patch
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Thanks,
Maxim
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Re: [bug#36875] [PATCH] doc: Document the use of `program-file' for mcron jobs. |
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Mon, 26 Aug 2019 07:54:58 +0900 |
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Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux) |
Hello Ludovic!
Ludovic Courtès <address@hidden> writes:
> Hello!
>
> Maxim Cournoyer <address@hidden> skribis:
>
>> From 0fffed46b4899bf0485926399d3971a4b5e94408 Mon Sep 17 00:00:00 2001
>> From: Maxim Cournoyer <address@hidden>
>> Date: Thu, 1 Aug 2019 07:34:17 +0900
>> Subject: [PATCH] doc: Document the use of `program-file' for mcron jobs.
>>
>> * doc/guix.texi (Scheduled Job Execution): Explain why using `program-file'
>> for an mcron job can be necessary. Add an example.
>
> [...]
>
>> +For more complex jobs defined in Scheme, it is safer to pass the job as a
>> +script to mcron; otherwise, macros defined or imported with
>> @code{use-modules}
>> +wouldn't expand correctly, as Guile requires macros to be strictly defined
>> or
>> +imported at the top level of a Guile module. This can be achieved using the
>> +@code{program-file} procedure from the @code{(guix gexp)} module, as shown
>> in
>> +the example below.
>
> Macros are a very good example of the problem, but I wonder if it would
> be clearer to simply write something like:
>
> For more complex jobs defined in Scheme where you need control over
> the top level, for instance to introduce a @code{use-modules} form, you
> can move your code to a separate program using the @code{program-file}
> procedure of the @code{(guix gexp)} module (@pxref{G-Expressions}).
> The example below illustrates that.
I like your version, which feels to me more elegant. But, from my
experimentation, using (use-modules) in a nested form is fine for
anything else than syntax (macros). Also, the Guile Reference only says
that macros must be *defined* at the top level; it doesn't explicitly
mention that importing macros is equivalent to defining macros, and are
thus subjected to the same restrictions. So, I've amended it to mention
the problem more precisely:
--8<---------------cut here---------------start------------->8---
For more complex jobs defined in Scheme where you need control over the top
level, for instance to introduce a @code{use-modules} form that defines syntax
(macros), you can move your code to a separate program using the
@code{program-file} procedure of the @code{(guix gexp)} module
(@pxref{G-Expressions}). The example below illustrates that.
--8<---------------cut here---------------end--------------->8---
> Anyway, your patch looks like a great improvement (and a funny example
> :-)) so IMO you should push one version or another!
This is now live as commit 1407ebeaa1. Thanks for feedback/review! :-)
Maxim
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