diff options
| -rw-r--r-- | gnu/services/configuration.scm | 16 |
1 files changed, 13 insertions, 3 deletions
diff --git a/gnu/services/configuration.scm b/gnu/services/configuration.scm index e2c4fe9998..a9426066b9 100644 --- a/gnu/services/configuration.scm +++ b/gnu/services/configuration.scm @@ -57,6 +57,7 @@ serialize-configuration define-maybe define-maybe/no-serialization + %unset-value maybe-value-set? generate-documentation configuration->documentation @@ -172,10 +173,10 @@ does not have a default value" field kind))) (values #'(field-type def))) ((field-type) (identifier? #'field-type) - (values #'(field-type 'unset))) + (values #'(field-type %unset-value))) (field-type (identifier? #'field-type) - (values #'(field-type 'unset))))) + (values #'(field-type %unset-value))))) (define (define-configuration-helper serialize? serializer-prefix syn) (syntax-case syn () @@ -301,9 +302,18 @@ does not have a default value" field kind))) (define (empty-serializer field-name val) "") (define serialize-package empty-serializer) +;; Ideally this should be an implementation detail, but we export it +;; to provide a simpler API that enables unsetting a configuration +;; field that has a maybe type, but also a default value. +;; +;; An example use-case would be something like a network application +;; that uses a default port, but the field can explicitly be unset to +;; request a random port at startup. +(define %unset-value 'unset) + (define (maybe-value-set? value) "Predicate to check whether a 'maybe' value was explicitly provided." - (not (eq? 'unset value))) + (not (eq? %unset-value value))) ;; A little helper to make it easier to document all those fields. (define (generate-documentation documentation documentation-name) |