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services: configuration: Add a 'maybe-value-set?' procedure.

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* gnu/services/configuration.scm (maybe-value-set?): New procedure.
* doc/guix.texi (Complex Configurations): Document it.  Remove comment showing
usage of 'maybe-string' with a default value, which doesn't make sense.

Co-authored-by: Attila Lendvai <attila@lendvai.name>
This commit is contained in:
Maxim Cournoyer
2022-08-24 14:40:38 +02:00
parent 31339f5f5f
commit 1c803e63f9
2 changed files with 16 additions and 6 deletions
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gnu/services/configuration.scm
+10 -5
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@@ -57,6 +57,7 @@
serialize-configuration
define-maybe
define-maybe/no-serialization
maybe-value-set?
generate-documentation
configuration->documentation
empty-serializer
@@ -142,7 +143,8 @@ does not have a default value" field kind)))
(id #'stem #'serialize-maybe- #'stem))))
#`(begin
(define (maybe-stem? val)
(or (eq? val 'unset) (stem? val)))
(or (not (maybe-value-set? val))
(stem? val)))
#,@(if serialize?
(list #'(define (serialize-maybe-stem field-name val)
(if (stem? val)
@@ -260,11 +262,10 @@ does not have a default value" field kind)))
(default-value-thunk
(lambda ()
(display '#,(id #'stem #'% #'stem))
(if (eq? (syntax->datum field-default)
'unset)
(if (maybe-value-set? (syntax->datum field-default))
field-default
(configuration-missing-default-value
'#,(id #'stem #'% #'stem) 'field)
field-default)))
'#,(id #'stem #'% #'stem) 'field))))
(documentation doc))
...))))))))
@@ -300,6 +301,10 @@ does not have a default value" field kind)))
(define (empty-serializer field-name val) "")
(define serialize-package empty-serializer)
(define (maybe-value-set? value)
"Predicate to check whether a 'maybe' value was explicitly provided."
(not (eq? 'unset value)))
;; A little helper to make it easier to document all those fields.
(define (generate-documentation documentation documentation-name)
(define (str x) (object->string x))