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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
parentbf307a7a54eeca405e5c6ad50a9cbe6b9e10190d (diff)
downloadguix-71654dfdda4890d7a663a36a7fe754b53591aba6.tar
guix-71654dfdda4890d7a663a36a7fe754b53591aba6.tar.gz
services: Add 'simple-service'.
* gnu/services.scm (simple-service): New procedure. * doc/guix.texi (Service Reference): Document it.
-rw-r--r--doc/guix.texi19
-rw-r--r--gnu/services.scm8
2 files changed, 27 insertions, 0 deletions
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
diff --git a/gnu/services.scm b/gnu/services.scm
index 5479bfae19..7e322c50b0 100644
--- a/gnu/services.scm
+++ b/gnu/services.scm
@@ -50,6 +50,7 @@
service-kind
service-parameters
+ simple-service
modify-services
service-back-edges
fold-services
@@ -141,6 +142,13 @@
(type service-kind)
(parameters service-parameters))
+(define (simple-service name target value)
+ "Return a service that extends TARGET with VALUE. This works by creating a
+singleton service type NAME, of which the returned service is an instance."
+ (let* ((extension (service-extension target identity))
+ (type (service-type (name name)
+ (extensions (list extension)))))
+ (service type value)))
(define-syntax %modify-service
(syntax-rules (=>)