[bug#63985,v4,5/5] services: configuration: Add some commonly used predicates.

diff --git a/doc/guix.texi b/doc/guix.texi
index e4a1523dfb..1deb784f56 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -28188,7 +28188,7 @@  Telephony Services
 connection to the Internet has been lost.  When left unspecified,
 the value from the account archive prevails.
 
-@item @code{bootstrap-hostnames} (type: maybe-string-list)
+@item @code{bootstrap-hostnames} (type: maybe-list-of-strings)
 A list of hostnames or IPs pointing to OpenDHT nodes, that should be
 used to initially join the OpenDHT network.  When left unspecified, the
 value from the account archive prevails.
@@ -34509,7 +34509,7 @@  Audio Services
 
 The default @code{%mpd-group} is a system group with name ``mpd''.
 
-@item @code{shepherd-requirement} (default: @code{'()}) (type: list-of-symbol)
+@item @code{shepherd-requirement} (default: @code{'()}) (type: list-of-symbols)
 A list of symbols naming Shepherd services that this service
 will depend on.
 
@@ -34759,7 +34759,7 @@  Audio Services
 @item @code{package} (default: @code{mympd}) (type: file-like)
 The package object of the myMPD server.
 
-@item @code{shepherd-requirement} (default: @code{'()}) (type: list-of-symbol)
+@item @code{shepherd-requirement} (default: @code{'()}) (type: list-of-symbols)
 This is a list of symbols naming Shepherd services that this service
 will depend on.
 
diff --git a/gnu/services/audio.scm b/gnu/services/audio.scm
index 260abdefed..ae991ced4d 100644
--- a/gnu/services/audio.scm
+++ b/gnu/services/audio.scm
@@ -138,9 +138,6 @@  (define (uglify-field-name field-name)
                                    str)
                                #\-) "_")))
 
-(define list-of-symbol?
-  (list-of symbol?))
-
 ;; Helpers for deprecated field types, to be removed later.
 (define %lazy-group (make-symbol "%lazy-group"))
 
@@ -428,7 +425,7 @@  (define-configuration mpd-configuration
    (sanitizer mpd-group-sanitizer))
 
   (shepherd-requirement
-   (list-of-symbol '())
+   (list-of-symbols '())
    "This is a list of symbols naming Shepherd services that this service
 will depend on."
    empty-serializer)
@@ -763,7 +760,7 @@  (define-configuration/no-serialization mympd-configuration
     empty-serializer)
 
   (shepherd-requirement
-   (list-of-symbol '())
+   (list-of-symbols '())
    "This is a list of symbols naming Shepherd services that this service
 will depend on."
    empty-serializer)
diff --git a/gnu/services/configuration.scm b/gnu/services/configuration.scm
index aa5fb832d5..d2b1687496 100644
--- a/gnu/services/configuration.scm
+++ b/gnu/services/configuration.scm
@@ -80,7 +80,9 @@  (define-module (gnu services configuration)
             interpose
             list-of
 
+            list-of-packages?
             list-of-strings?
+            list-of-symbols?
             alist?
             serialize-file-like
             text-config?
@@ -500,6 +502,11 @@  (define* (interpose ls  #:optional (delimiter "\n") (grammar 'infix))
                           (cons delimiter acc))))
               '() ls))
 
+
+;;;
+;;; Commonly used predicates
+;;;
+
 (define (list-of pred?)
   "Return a procedure that takes a list and check if all the elements of
 the list result in @code{#t} when applying PRED? on them."
@@ -508,10 +515,20 @@  (define (list-of pred?)
           (every pred? x)
           #f)))
 
+(define list-of-packages?
+  (list-of package?))
 
 (define list-of-strings?
   (list-of string?))
 
+(define list-of-symbols?
+  (list-of symbol?))
+
+
+;;;
+;;; Special serializers
+;;;
+
 (define alist?
   (list-of pair?))
 
diff --git a/gnu/services/telephony.scm b/gnu/services/telephony.scm
index 56b7772f58..c9b5d6cd99 100644
--- a/gnu/services/telephony.scm
+++ b/gnu/services/telephony.scm
@@ -117,15 +117,10 @@  (define (string-or-computed-file? val)
   (or (string? val)
       (computed-file? val)))
 
-(define (string-list? val)
-  (and (list? val)
-       (and-map string? val)))
+(define account-fingerprint-list?
+  (list-of account-fingerprint?))
 
-(define (account-fingerprint-list? val)
-  (and (list? val)
-       (and-map account-fingerprint? val)))
-
-(define-maybe string-list)
+(define-maybe list-of-strings)
 
 (define-maybe/no-serialization account-fingerprint-list)
 
@@ -135,7 +130,7 @@  (define-maybe string)
 
 ;;; The following serializers are used to derive an account details alist from
 ;;; a <jami-account> record.
-(define (serialize-string-list _ val)
+(define (serialize-list-of-strings _ val)
   (string-join val ";"))
 
 (define (serialize-boolean _ val)
@@ -188,7 +183,7 @@  (define-configuration jami-account
 connection to the the Internet has been lost.  When left unspecified, the
 value from the account archive prevails.")
   (bootstrap-hostnames
-   maybe-string-list
+   maybe-list-of-strings
    "A list of hostnames or IPs pointing to OpenDHT nodes, that should be used
 to initially join the OpenDHT network.  When left unspecified, the value from
 the account archive prevails.")
@@ -220,9 +215,8 @@  (define (jami-account->alist jami-account-object)
 
   (list-transduce jami-account-transducer rcons jami-account-fields))
 
-(define (jami-account-list? val)
-  (and (list? val)
-       (and-map jami-account? val)))
+(define jami-account-list?
+  (list-of jami-account?))
 
 (define-maybe/no-serialization jami-account-list)