profiles: Add generation manipulation procedures.

* guix/scripts/package.scm (delete-generations): Use
  'delete-generation*' instead of 'delete-generation'.
  (guix-package)[process-actions]: Use 'roll-back*' instead of
  'roll-back' and 'switch-to-generation*' instead of
  'switch-to-generation'.
  (link-to-empty-profile, switch-to-generation,
  switch-to-previous-generation, roll-back, delete-generation): Move
  to...
* guix/profiles.scm: ... here.  Adjust to not print messages and to
  return values that can be used by user interfaces.
* guix/ui.scm (display-generation-change, roll-back*,
  switch-to-generation*, delete-generation*): New procedures.

1 files changed, 24 insertions, 0 deletions

diff --git a/guix/ui.scm b/guix/ui.scm
index b7ed5e7d4d..72208e7de7 100644
--- a/guix/ui.scm
+++ b/guix/ui.scm
@@ -86,6 +86,9 @@
             matching-generations
             display-generation
             display-profile-content
+            roll-back*
+            switch-to-generation*
+            delete-generation*
             run-guix-command
             run-guix
             program-name
@@ -1035,6 +1038,27 @@ way."
              (manifest-entries
               (profile-manifest (generation-file-name profile number))))))
 
+(define (display-generation-change previous current)
+  (format #t (_ "switched from generation ~a to ~a~%") previous current))
+
+(define (roll-back* store profile)
+  "Like 'roll-back', but display what is happening."
+  (call-with-values
+      (lambda ()
+        (roll-back store profile))
+    display-generation-change))
+
+(define (switch-to-generation* profile number)
+  "Like 'switch-generation', but display what is happening."
+  (let ((previous (switch-to-generation profile number)))
+    (display-generation-change previous number)))
+
+(define (delete-generation* store profile generation)
+  "Like 'delete-generation', but display what is going on."
+  (format #t (_ "deleting ~a~%")
+          (generation-file-name profile generation))
+  (delete-generation store profile generation))
+
 (define* (package-specification->name+version+output spec
                                                      #:optional (output "out"))
   "Parse package specification SPEC and return three value: the specified