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doc: Clarify and consolidate modify-services documentation. 

* doc/guix.texi ("Using the Configuration System"): Move the example...
("Service Reference"): ...to here, and clarify more.
* gnu/services.scm (modify-services): Update docstring to mention the
return type.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>
master
Chris Marusich 2016-03-07 01:55:07 -08:00 committed by Ludovic Courtès
parent e3009f6000
commit 4d343a141b
2 changed files with 57 additions and 35 deletions
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87
doc/guix.texi
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@ -16,8 +16,9 @@ Copyright @copyright{} 2013 Nikita Karetnikov@*
Copyright @copyright{} 2015, 2016 Mathieu Lirzin@*
Copyright @copyright{} 2014 Pierre-Antoine Rault@*
Copyright @copyright{} 2015 Taylan Ulrich Bayırlı/Kammer@*
Copyright @copyright{} 2015, 2016 Leo Famulari
Copyright @copyright{} 2016 Ben Woodcroft
Copyright @copyright{} 2015, 2016 Leo Famulari@*
Copyright @copyright{} 2016 Ben Woodcroft@*
Copyright @copyright{} 2016 Chris Marusich
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
@ -6158,28 +6159,42 @@ generated as needed (@pxref{Defining Services}).
@cindex customization, of services
@findex modify-services
Occasionally, instead of using the base services as is, you will want to
customize them. For instance, to change the configuration of
@code{guix-daemon} and Mingetty (the console log-in), you may write the
following instead of @var{%base-services}:
customize them. To do this, use @code{modify-services} (@pxref{Service
Reference, @code{modify-services}}) to modify the list.
For example, suppose you want to modify @code{guix-daemon} and Mingetty
(the console log-in) in the @var{%base-services} list (@pxref{Base
Services, @code{%base-services}}). To do that, you can write the
following in your operating system declaration:
@lisp
(modify-services %base-services
(guix-service-type config =>
(guix-configuration
(inherit config)
(use-substitutes? #f)
(extra-options '("--gc-keep-outputs"))))
(mingetty-service-type config =>
(mingetty-configuration
(inherit config)
(motd (plain-file "motd" "Hi there!")))))
(define %my-services
;; My very own list of services.
(modify-services %base-services
(guix-service-type config =>
(guix-configuration
(inherit config)
(use-substitutes? #f)
(extra-options '("--gc-keep-derivations"))))
(mingetty-service-type config =>
(mingetty-configuration
(inherit config)
(motd (plain-file "motd" "Howdy!"))))))
(operating-system
;; @dots{}
(services %my-services))
@end lisp
@noindent
The effect here is to change the options passed to @command{guix-daemon}
when it is started, as well as the ``message of the day'' that appears
when logging in at the console. @xref{Service Reference,
@code{modify-services}}, for more on that.
This changes the configuration---i.e., the service parameters---of the
@code{guix-service-type} instance, and that of all the
@code{mingetty-service-type} instances in the @var{%base-services} list.
Observe how this is accomplished: first, we arrange for the original
configuration to be bound to the identifier @code{config} in the
@var{body}, and then we write the @var{body} so that it evaluates to the
desired configuration. In particular, notice how we use @code{inherit}
to create a new configuration which has the same values as the old
configuration, but with a few modifications.
The configuration for a typical ``desktop'' usage, with the X11 display
server, a desktop environment, network management, power management, and
@ -10035,11 +10050,12 @@ Here is an example of how a service is created and manipulated:
The @code{modify-services} form provides a handy way to change the
parameters of some of the services of a list such as
@var{%base-services} (@pxref{Base Services, @code{%base-services}}). Of
course, you could always use standard list combinators such as
@code{map} and @code{fold} to do that (@pxref{SRFI-1, List Library,,
guile, GNU Guile Reference Manual}); @code{modify-services} simply
provides a more concise form for this common pattern.
@var{%base-services} (@pxref{Base Services, @code{%base-services}}). It
evalutes to a list of services. Of course, you could always use
standard list combinators such as @code{map} and @code{fold} to do that
(@pxref{SRFI-1, List Library,, guile, GNU Guile Reference Manual});
@code{modify-services} simply provides a more concise form for this
common pattern.
@deffn {Scheme Syntax} modify-services @var{services} @
(@var{type} @var{variable} => @var{body}) @dots{}
@ -10051,16 +10067,21 @@ clauses. Each clause has the form:
(@var{type} @var{variable} => @var{body})
@end example
where @var{type} is a service type, such as @var{guix-service-type}, and
@var{variable} is an identifier that is bound within @var{body} to the
value of the service of that @var{type}. @xref{Using the Configuration
System}, for an example.
where @var{type} is a service type---e.g.,
@code{guix-service-type}---and @var{variable} is an identifier that is
bound within the @var{body} to the service parameters---e.g., a
@code{guix-configuration} instance---of the original service of that
@var{type}.
This is a shorthand for:
The @var{body} should evaluate to the new service parameters, which will
be used to configure the new service. This new service will replace the
original in the resulting list. Because a service's service parameters
are created using @code{define-record-type*}, you can write a succint
@var{body} that evaluates to the new service parameters by using the
@code{inherit} feature that @code{define-record-type*} provides.
@xref{Using the Configuration System} for example usage.
@example
(map (lambda (service) @dots{}) @var{services})
@end example
@end deffn
Next comes the programming interface for service types. This is

5
gnu/services.scm
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@ -1,5 +1,6 @@
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2015, 2016 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2016 Chris Marusich <cmmarusich@gmail.com>
;;;
;;; This file is part of GNU Guix.
;;;
@ -153,8 +154,8 @@
(define-syntax modify-services
(syntax-rules ()
"Modify the services listed in SERVICES according to CLAUSES. Each clause
must have the form:
"Modify the services listed in SERVICES according to CLAUSES and return
the resulting list of services. Each clause must have the form:
(TYPE VARIABLE => BODY)