Alex Kost <alezost@gmail.com> skribis:

> Ludovic Courtès (2016-07-28 01:19 +0300) wrote:
>
>> Alex Kost <alezost@gmail.com> skribis:

[...]

>>> From d7747453bf31a616d414dce293fc0556d601abcb Mon Sep 17 00:00:00 2001
>>> From: Alex Kost <alezost@gmail.com>
>>> Date: Wed, 27 Jul 2016 14:55:50 +0300
>>> Subject: [PATCH] emacs: Disable grafts when dry-run is enabled.
>>>
>>> * emacs/guix-main.scm (process-package-actions): Set grafting according
>>> to 'dry-run?'.
>>> * guix/scripts.scm (build-package): Likewise.
>>
>> [...]
>>
>>>  (define-module (guix scripts)
>>> +  #:use-module (guix grafts)
>>>    #:use-module (guix utils)
>>>    #:use-module (guix ui)
>>>    #:use-module (guix store)
>>> @@ -106,6 +107,7 @@ true."
>>>    "Build PACKAGE using BUILD-OPTIONS acceptable by 'set-build-options'.
>>>  Show what and how will/would be built."
>>>    (mbegin %store-monad
>>> +    (set-grafting (not dry-run?))
>>>      (apply set-build-options*
>>>             #:use-substitutes? use-substitutes?
>>>             (strip-keyword-arguments '(#:dry-run?) build-options))
>>
>> Here it might be best to do something like this:
>>
>>   (mlet %store-monad ((grafting? ((lift0 %graft? %store-monad))))
>>     (set-grafting (and (not dry-run?) grafting?))
>>     …)
>>
>> This would make sure we don’t enable grafting if it turned out to be
>> disabled.
>>
>> WDYT?
>
> OK, you know better :-)
>
> However, I tried it and it doesn't work for me (note: I know nothing
> about monads, gexps, etc.).  When I try this:
>
>    (mbegin %store-monad
>      (set-grafting #f)
>      …)
>
> the grafting doesn't happen, but when I try this:
>
>    (mlet %store-monad ((grafting? ((lift0 %graft? %store-monad))))
>      (set-grafting #f)
>      …)
>
> grafting happens anyway.  I have no idea what the problem is.

Hmm.  Not sure why.  What about this: