--- Begin Message ---
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Subject: |
“guix system” suggests wrong module import when using “remove” |
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Date: |
Sat, 09 May 2020 00:00:05 +0200 |
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User-agent: |
mu4e 1.2.0; emacs 26.3 |
I want to delete a service from %desktop-services, so I write
--8<---------------cut here---------------start------------->8---
…
(services (remove
(lambda (service)
(eq? (service-kind service) that-annoying-service-type))
%desktop-services))
…
--8<---------------cut here---------------end--------------->8---
Then I run “guix system build config.scm” and Guix tells me that it
doesn’t know what “remove” is:
--8<---------------cut here---------------start------------->8---
config.scm:56:18: error: remove: unbound variable
hint: Did you forget `(use-modules (rnrs lists))'?
--8<---------------cut here---------------end--------------->8---
I add the suggested module import to my file and it no longer complains,
but that-annoying-service-type has not actually been removed. Oh no!
Of course, the Guix manual says this:
--8<---------------cut here---------------start------------->8---
Again, ‘%desktop-services’ is just a list of service objects. If you
want to remove services from there, you can do so using the procedures
for list filtering (*note (guile)SRFI-1 Filtering and Partitioning::).
For instance, the following expression returns a list that contains all
the services in ‘%desktop-services’ minus the Avahi service:
(remove (lambda (service)
(eq? (service-kind service) avahi-service-type))
%desktop-services)
--8<---------------cut here---------------end--------------->8---
But maybe I don’t know what SRFI-1 is and I trust that the hint Guix
provides will be the right thing to do.
But now I’m curious and I look at the documentation for “remove” from
(rnrs lists):
--8<---------------cut here---------------start------------->8---
-- Scheme Procedure: remp proc list
-- Scheme Procedure: remove obj list
-- Scheme Procedure: remv obj list
-- Scheme Procedure: remq obj list
‘remove’, ‘remv’, and ‘remq’ are identical to the ‘delete’, ‘delv’,
and ‘delq’ procedures provided by Guile’s core library, (*note List
Modification::). ‘remp’ is identical to the alternate ‘remove’
procedure provided by SRFI-1; *Note SRFI-1 Deleting::.
--8<---------------cut here---------------end--------------->8---
Oh.
So here are my questions:
* can we prefer (srfi srfi-1) over (rnrs lists) in the suggestions for “remove”?
* can we avoid this by extending modify-services to support “delete”
much like modify-phases, and suggesting to use that instead of
“remove”?
--
Ricardo
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--- Begin Message ---
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Subject: |
Re: bug#41140: “guix system” suggests wrong module import when using “remove” |
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Date: |
Mon, 12 Apr 2021 18:21:08 +0200 |
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User-agent: |
mu4e 1.4.15; emacs 27.2 |
Ludovic Courtès <ludo@gnu.org> writes:
> Hi,
>
> Ricardo Wurmus <rekado@elephly.net> skribis:
>
>>>From 40c1208cbe9cbfa58ee385ef6ee06b775d309753 Mon Sep 17 00:00:00 2001
>> From: Ricardo Wurmus <rekado@elephly.net>
>> Date: Sun, 10 May 2020 23:29:38 +0200
>> Subject: [PATCH] services: Support DELETE in MODIFY-SERVICES macro.
>>
>> * gnu/services.scm (%modify-service): Add clause for DELETE syntax.
>> (modify-services): Use FILTER-MAP; adjust docstring.
>> * doc/guix.texi (System Services): Mention alternative syntax.
>> (X Window): Use MODIFY-SERVICES syntax.
>
> I like it!
>
>> - #:use-module (srfi srfi-1)
>> + #:use-module ((srfi srfi-1) #:hide (delete))
>> #:use-module (srfi srfi-9)
>> #:use-module (srfi srfi-9 gnu)
>> #:use-module (srfi srfi-26)
>> @@ -272,7 +273,11 @@ singleton service type NAME, of which the returned
>> service is an instance."
>> (service type value)))
>>
>> (define-syntax %modify-service
>> - (syntax-rules (=>)
>> + (syntax-rules (=> delete)
>> + ((_ svc (delete kind) clauses ...)
>> + (if (eq? (service-kind svc) kind)
>> + #f
>> + (%modify-service svc clauses ...)))
>
> Best practice suggests that ‘delete’ should be bound (info "(guile)
> Syntax Rules"):
>
> --8<---------------cut here---------------start------------->8---
> Although literals can be unbound, usually they are bound to allow
> them to be imported, exported, and renamed. *Note Modules::, for more
> information on imports and exports. In Guile there are a few standard
> auxiliary syntax definitions, as specified by R6RS and R7RS:
> --8<---------------cut here---------------end--------------->8---
>
> Now, if we export a new ‘delete’ binding from here, it’ll annoy
> everyone. So perhaps we can keep the srfi-1 ‘delete’ and re-export it,
> as done in (guix build utils)… though that situation is also annoying
> because we get warnings saying that it collides with core ‘delete’.
>
> Dunno, give it a try!
I finally did give it a try. I’m re-exporting “delete” and I don’t get
any warnings.
I pushed this with commit a247f5c7537df7e0c09051ba22d5c95eb08f48b9.
Thank you for the review and your comments!
--
Ricardo
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