05/07: channels: Use 'fold2'.

[guix-commits]

civodul pushed a commit to branch master
in repository guix.

commit f58f676b12254cdf5adb453798917b06ac6609a6
Author: Ludovic Courtès <address@hidden>
Date:   Sun Jan 20 18:45:40 2019 +0100

    channels: Use 'fold2'.
    
    * guix/channels.scm (latest-channel-instances): Use 'fold2' instead of
    'fold'.
---
 guix/channels.scm | 72 +++++++++++++++++++++++++++----------------------------
 1 file changed, 36 insertions(+), 36 deletions(-)

diff --git a/guix/channels.scm b/guix/channels.scm
index e588d86..10345c1 100644
--- a/guix/channels.scm
+++ b/guix/channels.scm
@@ -26,6 +26,7 @@
   #:use-module (guix monads)
   #:use-module (guix profiles)
   #:use-module (guix derivations)
+  #:use-module (guix combinators)
   #:use-module (guix store)
   #:use-module (guix i18n)
   #:use-module ((guix utils)
@@ -162,44 +163,43 @@ of previously processed channels."
                    (or (channel-commit b)
                        (not (or (channel-commit a)
                                 (channel-commit b))))))))
+
   ;; Accumulate a list of instances.  A list of processed channels is also
   ;; accumulated to decide on duplicate channel specifications.
-  (match (fold (lambda (channel acc)
-                 (match acc
-                   ((#:channels previous-channels #:instances instances)
-                    (if (ignore? channel previous-channels)
-                        acc
-                        (begin
-                          (format (current-error-port)
-                                  (G_ "Updating channel '~a' from Git 
repository at '~a'...~%")
-                                  (channel-name channel)
-                                  (channel-url channel))
-                          (let-values (((checkout commit)
-                                        (latest-repository-commit store 
(channel-url channel)
-                                                                  #:ref 
(channel-reference
-                                                                         
channel))))
-                            (let ((instance (channel-instance channel commit 
checkout)))
-                              (let-values (((new-instances new-channels)
-                                            (latest-channel-instances
-                                             store
-                                             (channel-instance-dependencies 
instance)
-                                             previous-channels)))
-                                `(#:channels
-                                  ,(append (cons channel new-channels)
-                                           previous-channels)
-                                  #:instances
-                                  ,(append (cons instance new-instances)
-                                           instances))))))))))
-               `(#:channels ,previous-channels #:instances ())
-               channels)
-    ((#:channels channels #:instances instances)
-     (let ((instance-name (compose channel-name channel-instance-channel)))
-       ;; Remove all earlier channel specifications if they are followed by a
-       ;; more specific one.
-       (values (delete-duplicates instances
-                                  (lambda (a b)
-                                    (eq? (instance-name a) (instance-name b))))
-               channels)))))
+  (define-values (resulting-channels instances)
+    (fold2 (lambda (channel previous-channels instances)
+             (if (ignore? channel previous-channels)
+                 (values previous-channels instances)
+                 (begin
+                   (format (current-error-port)
+                           (G_ "Updating channel '~a' from Git repository at 
'~a'...~%")
+                           (channel-name channel)
+                           (channel-url channel))
+                   (let-values (((checkout commit)
+                                 (latest-repository-commit store (channel-url 
channel)
+                                                           #:ref 
(channel-reference
+                                                                  channel))))
+                     (let ((instance (channel-instance channel commit 
checkout)))
+                       (let-values (((new-instances new-channels)
+                                     (latest-channel-instances
+                                      store
+                                      (channel-instance-dependencies instance)
+                                      previous-channels)))
+                         (values (append (cons channel new-channels)
+                                         previous-channels)
+                                 (append (cons instance new-instances)
+                                         instances))))))))
+           previous-channels
+           '()                                    ;instances
+           channels))
+
+  (let ((instance-name (compose channel-name channel-instance-channel)))
+    ;; Remove all earlier channel specifications if they are followed by a
+    ;; more specific one.
+    (values (delete-duplicates instances
+                               (lambda (a b)
+                                 (eq? (instance-name a) (instance-name b))))
+            resulting-channels)))
 
 (define* (checkout->channel-instance checkout
                                      #:key commit