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authorLudovic Courtès <ludo@gnu.org>2016-09-19 13:31:06 +0900
committerLudovic Courtès <ludo@gnu.org>2016-09-19 23:11:19 +0900
commit71654dfdda4890d7a663a36a7fe754b53591aba6 (patch)
treefda1be459091f59487413a53b791bdd68cbb46c8 /doc
parentbf307a7a54eeca405e5c6ad50a9cbe6b9e10190d (diff)
services: Add 'simple-service'.
* gnu/services.scm (simple-service): New procedure. * doc/guix.texi (Service Reference): Document it.
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diff --git a/doc/guix.texi b/doc/guix.texi
index 7a86a2f0ac..808fbdceb4 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -11348,6 +11348,25 @@ the extension; it must return a valid value for the target service.
Return true if @var{obj} is a service extension.
@end deffn
+Occasionally, you might want to simply extend an existing service. This
+involves creating a new service type and specifying the extension of
+interest, which can be verbose; the @code{simple-service} procedure
+provides a shorthand for this.
+
+@deffn {Scheme Procedure} simple-service @var{name} @var{target} @var{value}
+Return a service that extends @var{target} with @var{value}. This works
+by creating a singleton service type @var{name}, of which the returned
+service is an instance.
+
+For example, this extends mcron (@pxref{Scheduled Job Execution}) with
+an additional job:
+
+@example
+(simple-service 'my-mcron-job mcron-service-type
+ #~(job '(next-hour (3)) "guix gc -F 2G"))
+@end example
+@end deffn
+
At the core of the service abstraction lies the @code{fold-services}
procedure, which is responsible for ``compiling'' a list of services
down to a single directory that contains everything needed to boot and