From: Chris Marusich <cmmarusich@gmail.com>
To: "Ludovic Courtès" <ludo@gnu.org>
Cc: guix-devel@gnu.org
Subject: Re: Incorrect service documentation?
Date: Thu, 29 Mar 2018 07:38:11 +0200 [thread overview]
Message-ID: <87lgebsapo.fsf@gmail.com> (raw)
In-Reply-To: <878taff103.fsf@gnu.org> ("Ludovic \=\?utf-8\?Q\?Court\=C3\=A8s\=22'\?\= \=\?utf-8\?Q\?s\?\= message of "Mon, 26 Mar 2018 14:57:16 +0200")
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ludo@gnu.org (Ludovic Courtès) writes:
> Hello!
>
> Chris Marusich <cmmarusich@gmail.com> skribis:
>
>> Is the description of "compose" correct? The manual claims that it
>> "must return a value that is a valid parameter value for the service
>> instance," but I do not think that is actually true. Judging by the
>> implementation of fold-services in (gnu services), it may return any
>> single value as long as the extend procedure knows how to handle it. In
>> fact, it is the "extend" procedure which must return a valid parameter
>> value for the service.
>
> Yes, you’re right! Good catch.
Thank you for confirming my understanding!
>> If this is true, then I suggest we change the documentation as follows:
>>
>> ‘compose’ (default: ‘#f’)
>> If this is ‘#f’, then the service type denotes services that
>> cannot be extended—i.e., services that do not receive “values”
>> from other services.
>>
>> Otherwise, it must be a one-argument procedure. The procedure
>> is called by ‘fold-services’ and is passed a list of values
>> collected from extensions. It may return any single value.
>>
>> ‘extend’ (default: ‘#f’)
>> If this is ‘#f’, services of this type cannot be extended.
>>
>> Otherwise, it must be a two-argument procedure:
>> ‘fold-services’ calls it, passing it the initial value of the
>> service as the first argument and the result of applying
>> ‘compose’ to the extension values as the second argument. It
>> must return a value that is a valid parameter value for the
>> service instance.
>>
>> What do you think?
>
> LGTM!
I've committed this as 881c61d06222a30dbffbf9d039eaca2abd3d22b3.
--
Chris
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prev parent reply other threads:[~2018-03-29 5:38 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-23 10:09 Incorrect service documentation? Chris Marusich
2018-03-26 12:57 ` Ludovic Courtès
2018-03-29 5:38 ` Chris Marusich [this message]
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