services: audio: Remove redundant list-of-string? predicate.

Use list-of-strings? predicate defined in (gnu services configuration).

* gnu/services/audio.scm (list-of-string?): Remove predicate.
(mpd-serialize-list-of-string): Rename procedure to ...
(mpd-serialize-list-of-strings): ... this.
(mpd-configuration)[environment-variables]: Switch to list-of-strings.
[endpoints]: Switch to maybe-list-of-strings.
(mympd-ip-acl)[allow, deny]: Switch to list-of-strings.
(mympd-serialize-configuration): Rename serialize-list-of-string to
serialize-list-of-strings.
* doc/guix.texi (Audio Services): Update it.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>

doc/guix.texi

@@ -33501,7 +33501,7 @@ The group to run mpd as.
 This is a list of symbols naming Shepherd services that this service
 will depend on.
 
-@item @code{environment-variables} (default: @code{()}) (type: list-of-string)
+@item @code{environment-variables} (default: @code{()}) (type: list-of-strings)
 A list of strings specifying environment variables.
 
 @item @code{log-file} (default: @code{"/var/log/mpd/log"}) (type: maybe-string)
@@ -33532,7 +33532,7 @@ The location of the sticker database.
 @item @code{default-port} (default: @code{6600}) (type: maybe-integer)
 The default port to run mpd on.
 
-@item @code{endpoints} (type: maybe-list-of-string)
+@item @code{endpoints} (type: maybe-list-of-strings)
 The addresses that mpd will bind to.  A port different from @var{default-port}
 may be specified, e.g. @code{localhost:6602} and IPv6 addresses must be
 enclosed in square brackets when a different port is used.
@@ -33808,10 +33808,10 @@ Whether to preserve caches between service restarts.
 Available @code{mympd-ip-acl} fields are:
 
 @table @asis
-@item @code{allow} (default: @code{()}) (type: list-of-string)
+@item @code{allow} (default: @code{()}) (type: list-of-strings)
 Allowed IP addresses.
 
-@item @code{deny} (default: @code{()}) (type: list-of-string)
+@item @code{deny} (default: @code{()}) (type: list-of-strings)
 Disallowed IP addresses.
 
 @end table

gnu/services/audio.scm

@@ -2,7 +2,7 @@
 ;;; Copyright © 2017 Peter Mikkelsen <petermikkelsen10@gmail.com>
 ;;; Copyright © 2019 Ricardo Wurmus <rekado@elephly.net>
 ;;; Copyright © 2020 Ludovic Courtès <ludo@gnu.org>
-;;; Copyright © 2022 Bruno Victal <mirai@makinata.eu>
+;;; Copyright © 2022⁠–⁠2023 Bruno Victal <mirai@makinata.eu>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -137,9 +137,6 @@
                                    str)
                                #\-) "_")))
 
-(define list-of-string?
-  (list-of string?))
-
 (define list-of-symbol?
   (list-of symbol?))
 
@@ -159,11 +156,11 @@
 (define mpd-serialize-string mpd-serialize-field)
 (define mpd-serialize-boolean mpd-serialize-field)
 
-(define (mpd-serialize-list-of-string field-name value)
+(define (mpd-serialize-list-of-strings field-name value)
   #~(string-append #$@(map (cut mpd-serialize-string field-name <>) value)))
 
 (define-maybe string (prefix mpd-))
-(define-maybe list-of-string (prefix mpd-))
+(define-maybe list-of-strings (prefix mpd-))
 (define-maybe boolean (prefix mpd-))
 
 ;;; TODO: Procedures for deprecated fields, to be removed.
@@ -349,7 +346,7 @@ will depend on."
    empty-serializer)
 
   (environment-variables
-   (list-of-string '())
+   (list-of-strings '())
    "A list of strings specifying environment variables."
    empty-serializer)
 
@@ -400,7 +397,7 @@ Available values: @code{notice}, @code{info}, @code{verbose},
    "The default port to run mpd on.")
 
   (endpoints
-   maybe-list-of-string
+   maybe-list-of-strings
    "The addresses that mpd will bind to. A port different from
 @var{default-port} may be specified, e.g. @code{localhost:6602} and
 IPv6 addresses must be enclosed in square brackets when a different
@@ -409,7 +406,7 @@ To use a Unix domain socket, an absolute path or a path starting with @code{~}
 can be specified here."
    (lambda (_ endpoints)
      (if (maybe-value-set? endpoints)
-         (mpd-serialize-list-of-string "bind_to_address" endpoints)
+         (mpd-serialize-list-of-strings "bind_to_address" endpoints)
          "")))
 
   (address ; TODO: deprecated, remove later
@@ -581,11 +578,11 @@ appended to the configuration.")
 
 (define-configuration/no-serialization mympd-ip-acl
   (allow
-   (list-of-string '())
+   (list-of-strings '())
    "Allowed IP addresses.")
 
   (deny
-   (list-of-string '())
+   (list-of-strings '())
    "Disallowed IP addresses."))
 
 (define-maybe/no-serialization integer)
@@ -707,12 +704,12 @@ prompting a pin from the user.")
       ((? string? val) val)))
 
   (define (ip-acl-serialize-configuration config)
-    (define (serialize-list-of-string prefix lst)
+    (define (serialize-list-of-strings prefix lst)
       (map (cut format #f "~a~a" prefix <>) lst))
     (string-join
      (append
-      (serialize-list-of-string "+" (mympd-ip-acl-allow config))
+      (serialize-list-of-strings "+" (mympd-ip-acl-allow config))
-      (serialize-list-of-string "-" (mympd-ip-acl-deny config))) ","))
+      (serialize-list-of-strings "-" (mympd-ip-acl-deny config))) ","))
 
   ;; myMPD configuration fields are serialized as individual files under
   ;; <work-directory>/config/.