system: Account skeleton API is non-monadic.

* gnu/system/shadow.scm (default-skeletons): Use the non-monadic
  procedures and turn into a regular procedure.
  (skeleton-directory): Likewise.
* gnu/system.scm (etc-directory): Adjust accordingly.

gnu/system.scm

@@ -527,7 +527,7 @@ then
   # as those in ~/.guix-profile and /run/current-system/profile.
   source /run/current-system/profile/etc/profile.d/bash_completion.sh
 fi\n"))
-       (skel      (skeleton-directory skeletons)))
+       (skel ->   (skeleton-directory skeletons)))
     (file-union "etc"
                 `(("services" ,#~(string-append #$net-base "/etc/services"))
                   ("protocols" ,#~(string-append #$net-base "/etc/protocols"))

gnu/system/shadow.scm

@@ -20,7 +20,6 @@
   #:use-module (guix records)
   #:use-module (guix gexp)
   #:use-module (guix store)
-  #:use-module (guix monads)
   #:use-module (guix sets)
   #:use-module (guix ui)
   #:use-module ((gnu system file-systems)
@@ -133,10 +132,10 @@
         (copy-file (car (find-files #$guile-wm "wm-init-sample.scm"))
                    #$output)))
 
-  (mlet %store-monad ((profile (text-file "bash_profile" "\
+  (let ((profile (plain-file "bash_profile" "\
 # Honor per-interactive-shell startup file
 if [ -f ~/.bashrc ]; then . ~/.bashrc; fi\n"))
-                      (bashrc (text-file "bashrc" "\
+        (bashrc  (plain-file "bashrc" "\
 # Bash initialization for interactive non-login shells and
 # for remote shells (info \"(bash) Bash Startup Files\").
 
@@ -162,28 +161,27 @@ else
 fi
 alias ls='ls -p --color'
 alias ll='ls -l'\n"))
-                      (zlogin (text-file "zlogin" "\
+        (zlogin    (plain-file "zlogin" "\
 # Honor system-wide environment variables
 source /etc/profile\n"))
-                      (guile-wm (gexp->derivation "guile-wm" copy-guile-wm
-                                                  #:modules
-                                                  '((guix build utils))))
-                      (xdefaults (text-file "Xdefaults" "\
+        (guile-wm  (computed-file "guile-wm" copy-guile-wm
+                                  #:modules '((guix build utils))))
+        (xdefaults (plain-file "Xdefaults" "\
 XTerm*utf8: always
 XTerm*metaSendsEscape: true\n"))
-                      (gdbinit   (text-file "gdbinit" "\
+        (gdbinit   (plain-file "gdbinit" "\
 # Tell GDB where to look for separate debugging files.
 set debug-file-directory ~/.guix-profile/lib/debug\n")))
-    (return `((".bash_profile" ,profile)
+    `((".bash_profile" ,profile)
       (".bashrc" ,bashrc)
       (".zlogin" ,zlogin)
       (".Xdefaults" ,xdefaults)
       (".guile-wm" ,guile-wm)
-              (".gdbinit" ,gdbinit)))))
+      (".gdbinit" ,gdbinit))))
 
 (define (skeleton-directory skeletons)
-  "Return a directory containing SKELETONS, a list of name/derivation pairs."
-  (gexp->derivation "skel"
+  "Return a directory containing SKELETONS, a list of name/derivation tuples."
+  (computed-file "skel"
                  #~(begin
                      (use-modules (ice-9 match))