services: boot: Take gexps instead of monadic gexps.

* gnu/services.scm (compute-boot-script): Rename 'mexps' to 'gexps' and
remove 'mlet' form.
(boot-service-type): Update comment.
(cleanup-gexp): Remove 'with-monad' and 'return'.
(activation-script): Rewrite in non-monadic style: use 'scheme-file'
instead of 'gexp->file'.
(gexps->activation-gexp): Remove 'mlet', return a gexp.
* gnu/services/shepherd.scm (shepherd-boot-gexp): Remove 'with-monad'
and 'return'.
* gnu/system.scm (operating-system-boot-script): Remove outdated comment.
* gnu/tests/base.scm (%cleanup-os): For 'dirty-service', remove
'with-monad' and 'return'.

gnu/services.scm

@@ -337,15 +337,14 @@ containing the given entries."
 turn refers to everything the operating system needs: its kernel, initrd,
 system profile, boot script, and so on.")))
 
-(define (compute-boot-script _ mexps)
+(define (compute-boot-script _ gexps)
-  ;; Reverse MEXPS so that extensions appear in the boot script in the right
+  ;; Reverse GEXPS so that extensions appear in the boot script in the right
   ;; order.  That is, user extensions would come first, and extensions added
   ;; by 'essential-services' (e.g., running shepherd) are guaranteed to come
   ;; last.
-  (mlet %store-monad ((gexps (sequence %store-monad (reverse mexps))))
   (gexp->file "boot"
               ;; Clean up and activate the system, then spawn shepherd.
-                #~(begin #$@gexps))))
+              #~(begin #$@(reverse gexps))))
 
 (define (boot-script-entry mboot)
   "Return, as a monadic value, an entry for the boot script in the system
@@ -354,9 +353,9 @@ directory."
     (return `(("boot" ,boot)))))
 
 (define boot-service-type
-  ;; The service of this type is extended by being passed gexps as monadic
+  ;; The service of this type is extended by being passed gexps.  It
-  ;; values.  It aggregates them in a single script, as a monadic value, which
+  ;; aggregates them in a single script, as a monadic value, which becomes its
-  ;; becomes its 'parameters'.  It is the only service that extends nothing.
+  ;; value.
   (service-type (name 'boot)
                 (extensions
                  (list (service-extension system-service-type
@@ -372,11 +371,9 @@ by the initrd once the root file system is mounted.")))
   (service boot-service-type #t))
 
 (define (cleanup-gexp _)
-  "Return as a monadic value a gexp to clean up /tmp and similar places upon
+  "Return a gexp to clean up /tmp and similar places upon boot."
-boot."
-  (with-monad %store-monad
   (with-imported-modules '((guix build utils))
-      (return #~(begin
+    #~(begin
         (use-modules (guix build utils))
 
         ;; Clean out /tmp and /var/run.
@@ -413,7 +410,7 @@ boot."
            (chmod "/tmp" #o1777)
            (mkdir "/var/run")
            (chmod "/var/run" #o755)
-                     (delete-file-recursively "/run/udev/watch.old"))))))))
+           (delete-file-recursively "/run/udev/watch.old"))))))
 
 (define cleanup-service-type
   ;; Service that cleans things up in /tmp and similar.
@@ -432,14 +429,10 @@ ACTIVATION-SCRIPT-TYPE."
 
 (define (activation-script gexps)
   "Return the system's activation script, which evaluates GEXPS."
-  (define (service-activations)
+  (define actions
-    ;; Return the activation scripts for SERVICES.
+    (map (cut scheme-file "activate-service" <>) gexps))
-    (mapm %store-monad
-          (cut gexp->file "activate-service" <>)
-          gexps))
 
-  (mlet* %store-monad ((actions (service-activations)))
+  (scheme-file "activate"
-    (gexp->file "activate"
                (with-imported-modules (source-module-closure
                                        '((gnu build activation)
                                          (guix build utils)))
@@ -464,12 +457,11 @@ ACTIVATION-SCRIPT-TYPE."
 
                      ;; Run the services' activation snippets.
                      ;; TODO: Use 'load-compiled'.
-                      (for-each primitive-load '#$actions))))))
+                     (for-each primitive-load '#$actions)))))
 
 (define (gexps->activation-gexp gexps)
   "Return a gexp that runs the activation script containing GEXPS."
-  (mlet %store-monad ((script (activation-script gexps)))
+  #~(primitive-load #$(activation-script gexps)))
-    (return #~(primitive-load #$script))))
 
 (define (second-argument a b) b)
 

gnu/services/shepherd.scm

@@ -22,7 +22,6 @@
   #:use-module (guix sets)
   #:use-module (guix gexp)
   #:use-module (guix store)
-  #:use-module (guix monads)
   #:use-module (guix records)
   #:use-module (guix derivations)                 ;imported-modules, etc.
   #:use-module (gnu services)
@@ -66,8 +65,7 @@
 
 
 (define (shepherd-boot-gexp services)
-  (with-monad %store-monad
+  #~(begin
-    (return #~(begin
       ;; Keep track of the booted system.
       (false-if-exception (delete-file "/run/booted-system"))
       (symlink (readlink "/run/current-system")
@@ -85,7 +83,7 @@
       ;; Start shepherd.
       (execl #$(file-append shepherd "/bin/shepherd")
              "shepherd" "--config"
-                       #$(shepherd-configuration-file services))))))
+             #$(shepherd-configuration-file services))))
 
 (define shepherd-root-service-type
   (service-type

gnu/system.scm

@@ -819,7 +819,6 @@ we're running in the final root.  When CONTAINER? is true, skip all
 hardware-related operations as necessary when booting a Linux container."
   (let* ((services (operating-system-services os #:container? container?))
          (boot     (fold-services services #:target-type boot-service-type)))
-    ;; BOOT is the script as a monadic value.
     (service-value boot)))
 
 (define (operating-system-user-accounts os)

gnu/tests/base.scm

@@ -484,7 +484,6 @@ in a loop.  See <http://bugs.gnu.org/26931>.")
   (simple-operating-system
    (simple-service 'dirty-things
                    boot-service-type
-                   (with-monad %store-monad
                    (let ((script (plain-file
                                   "create-utf8-file.sh"
                                   (string-append
@@ -493,11 +492,11 @@ in a loop.  See <http://bugs.gnu.org/26931>.")
                                    "touch /witness\n"
                                    "exec touch /tmp/λαμβδα"))))
                      (with-imported-modules '((guix build utils))
-                         (return #~(begin
+                       #~(begin
                            (setenv "PATH"
                                    #$(file-append coreutils "/bin"))
                            (invoke #$(file-append bash "/bin/sh")
-                                             #$script)))))))))
+                                   #$script)))))))
 
 (define (run-cleanup-test name)
   (define os