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-rw-r--r--gnu/services/configuration.scm38
1 files changed, 33 insertions, 5 deletions
diff --git a/gnu/services/configuration.scm b/gnu/services/configuration.scm
index ecc5049a79..aa5fb832d5 100644
--- a/gnu/services/configuration.scm
+++ b/gnu/services/configuration.scm
@@ -42,6 +42,7 @@
#:use-module (srfi srfi-26)
#:use-module (srfi srfi-34)
#:use-module (srfi srfi-35)
+ #:use-module (srfi srfi-171)
#:export (configuration-field
configuration-field-name
configuration-field-type
@@ -59,6 +60,10 @@
define-configuration/no-serialization
no-serialization
+ empty-serializer?
+ tfilter-maybe-value
+ base-transducer
+
serialize-configuration
define-maybe
define-maybe/no-serialization
@@ -125,13 +130,36 @@ does not have a default value" field kind)))
(default-value-thunk configuration-field-default-value-thunk)
(documentation configuration-field-documentation))
+(define (empty-serializer? field)
+ "Predicate that checks whether FIELD is exempt from serialization."
+ (eq? empty-serializer
+ (configuration-field-serializer field)))
+
+(define (tfilter-maybe-value config)
+ "Return a transducer for CONFIG that removes all maybe-type fields whose
+value is '%unset-marker."
+ (tfilter (lambda (field)
+ (let ((field-value ((configuration-field-getter field) config)))
+ (maybe-value-set? field-value)))))
+
+(define (base-transducer config)
+ "Return a transducer for CONFIG that calls the serializing procedures only
+for fields marked for serialization and whose values are not '%unset-marker."
+ (compose (tremove empty-serializer?)
+ ;; Only serialize fields whose value isn't '%unset-marker%.
+ (tfilter-maybe-value config)
+ (tmap (lambda (field)
+ ((configuration-field-serializer field)
+ (configuration-field-name field)
+ ((configuration-field-getter field) config))))))
+
(define (serialize-configuration config fields)
+ "Return a G-expression that contains the values corresponding to the
+FIELDS of CONFIG, a record that has been generated by `define-configuration'.
+The G-expression can then be serialized to disk by using something like
+`mixed-text-file'."
#~(string-append
- #$@(map (lambda (field)
- ((configuration-field-serializer field)
- (configuration-field-name field)
- ((configuration-field-getter field) config)))
- fields)))
+ #$@(list-transduce (base-transducer config) rcons fields)))
(define-syntax-rule (id ctx parts ...)
"Assemble PARTS into a raw (unhygienic) identifier."