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-rw-r--r--gnu/services.scm42
1 files changed, 42 insertions, 0 deletions
diff --git a/gnu/services.scm b/gnu/services.scm
index d0fe0ade17..818252386f 100644
--- a/gnu/services.scm
+++ b/gnu/services.scm
@@ -48,6 +48,7 @@
service-kind
service-parameters
+ modify-services
service-back-edges
fold-services
@@ -133,6 +134,47 @@
(parameters service-parameters))
+(define-syntax %modify-service
+ (syntax-rules (=>)
+ ((_ service)
+ service)
+ ((_ svc (kind param => exp ...) clauses ...)
+ (if (eq? (service-kind svc) kind)
+ (let ((param (service-parameters svc)))
+ (service (service-kind svc)
+ (begin exp ...)))
+ (%modify-service svc clauses ...)))))
+
+(define-syntax modify-services
+ (syntax-rules ()
+ "Modify the services listed in SERVICES according to CLAUSES. Each clause
+must have the form:
+
+ (TYPE VARIABLE => BODY)
+
+where TYPE is a service type, such as 'guix-service-type', and VARIABLE is an
+identifier that is bound within BODY to the value of the service of that
+TYPE. Consider this example:
+
+ (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\" \"Hi there!\")))))
+
+It changes the configuration of the GUIX-SERVICE-TYPE instance, and that of
+all the MINGETTY-SERVICE-TYPE instances.
+
+This is a shorthand for (map (lambda (svc) ...) %base-services)."
+ ((_ services clauses ...)
+ (map (lambda (service)
+ (%modify-service service clauses ...))
+ services))))
;;;