From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: Why is "append" the activation service's "compose" procedure?
Date: Mon, 26 Mar 2018 15:02:36 +0200
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In-Reply-To: <87muyzdrjq.fsf@gmail.com> (Chris Marusich's message of "Fri, 23
	Mar 2018 11:17:45 +0100")
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To: Chris Marusich <cmmarusich@gmail.com>
Cc: guix-devel@gnu.org

Hello,

Chris Marusich <cmmarusich@gmail.com> skribis:

> This is our current definition of the activation-service-type (in (gnu
> services)):
>
>   (define activation-service-type
>     (service-type (name 'activate)
>                   (extensions
>                    (list (service-extension boot-service-type
>                                             gexps->activation-gexp)))
>                   (compose append)
>                   (extend second-argument)))
>
> Note that the the append procedure is used as the "compose" procedure.
> However, fold-services applies the "compose" procedure to a single list.
> What happens when you apply the append procedure to a single list?  You
> get the same list back:
>
>   scheme@(guile-user)> (define mylist '(1 2 3))
>   scheme@(guile-user)> (append mylist)
>   $1 =3D (1 2 3)
>   scheme@(guile-user)> (eq? mylist (append mylist))
>   $2 =3D #t
>
> The fold-services procedure always applies the "compose" procedure to a
> single list.  So why does the activation-service-type use the append
> procedure as its "compose" procedure?  Wouldn't it more accurately
> reflect our intent if we used the identity procedure instead?

Yes, you=E2=80=99re right here as well.  :-)

=E2=80=98boot-service-type=E2=80=99 has the same problem.

Can you fix both?

Thanks!

Ludo=E2=80=99.