emacs: Add 'guix-ui-read-profile'.

* emacs/guix-ui.el (guix-ui-read-profile): New procedure.
* emacs/guix-ui-package.el (guix-search-by-name)
  (guix-search-by-regexp, guix-installed-packages)
  (guix-obsolete-packages, guix-all-available-packages)
  (guix-newest-available-packages): Use it.
* emacs/guix-ui-generation.el (guix-generations)
  (guix-last-generations, guix-generations-by-time): Use it.

emacs/guix-ui-generation.el

@@ -401,9 +401,7 @@ GENERATION is a generation number of the current profile."
   "Display information about all generations.
 If PROFILE is nil, use `guix-current-profile'.
 Interactively with prefix, prompt for PROFILE."
-  (interactive
-   (list (and current-prefix-arg
-              (guix-profile-prompt))))
+  (interactive (list (guix-ui-read-profile)))
   (guix-generation-get-display profile 'all))
 
 ;;;###autoload
@@ -413,8 +411,7 @@ If PROFILE is nil, use `guix-current-profile'.
 Interactively with prefix, prompt for PROFILE."
   (interactive
    (list (read-number "The number of last generations: ")
-         (and current-prefix-arg
-              (guix-profile-prompt))))
+         (guix-ui-read-profile)))
   (guix-generation-get-display profile 'last number))
 
 ;;;###autoload
@@ -426,8 +423,7 @@ Interactively with prefix, prompt for PROFILE."
   (interactive
    (list (guix-read-date "Find generations (from): ")
          (guix-read-date "Find generations (to): ")
-         (and current-prefix-arg
-              (guix-profile-prompt))))
+         (guix-ui-read-profile)))
   (guix-generation-get-display profile 'time
                                (float-time from)
                                (float-time to)))

emacs/guix-ui-package.el

@@ -886,8 +886,7 @@ If PROFILE is nil, use `guix-current-profile'.
 Interactively with prefix, prompt for PROFILE."
   (interactive
    (list (read-string "Package name: " nil 'guix-package-search-history)
-         (and current-prefix-arg
-              (guix-profile-prompt))))
+         (guix-ui-read-profile)))
   (guix-package-get-display profile 'name name))
 
 ;;;###autoload
@@ -900,9 +899,7 @@ If PROFILE is nil, use `guix-current-profile'.
 Interactively with prefix, prompt for PROFILE."
   (interactive
    (list (read-regexp "Regexp: " nil 'guix-package-search-history)
-         nil
-         (and current-prefix-arg
-              (guix-profile-prompt))))
+         nil (guix-ui-read-profile)))
   (guix-package-get-display profile 'regexp regexp
                             (or params guix-package-search-params)))
 
@@ -911,9 +908,7 @@ Interactively with prefix, prompt for PROFILE."
   "Display information about installed Guix packages.
 If PROFILE is nil, use `guix-current-profile'.
 Interactively with prefix, prompt for PROFILE."
-  (interactive
-   (list (and current-prefix-arg
-              (guix-profile-prompt))))
+  (interactive (list (guix-ui-read-profile)))
   (guix-package-get-display profile 'installed))
 
 ;;;###autoload
@@ -921,9 +916,7 @@ Interactively with prefix, prompt for PROFILE."
   "Display information about obsolete Guix packages.
 If PROFILE is nil, use `guix-current-profile'.
 Interactively with prefix, prompt for PROFILE."
-  (interactive
-   (list (and current-prefix-arg
-              (guix-profile-prompt))))
+  (interactive (list (guix-ui-read-profile)))
   (guix-package-get-display profile 'obsolete))
 
 ;;;###autoload
@@ -931,9 +924,7 @@ Interactively with prefix, prompt for PROFILE."
   "Display information about all available Guix packages.
 If PROFILE is nil, use `guix-current-profile'.
 Interactively with prefix, prompt for PROFILE."
-  (interactive
-   (list (and current-prefix-arg
-              (guix-profile-prompt))))
+  (interactive (list (guix-ui-read-profile)))
   (guix-package-get-display profile 'all-available))
 
 ;;;###autoload
@@ -941,9 +932,7 @@ Interactively with prefix, prompt for PROFILE."
   "Display information about the newest available Guix packages.
 If PROFILE is nil, use `guix-current-profile'.
 Interactively with prefix, prompt for PROFILE."
-  (interactive
-   (list (and current-prefix-arg
-              (guix-profile-prompt))))
+  (interactive (list (guix-ui-read-profile)))
   (guix-package-get-display profile 'newest-available))
 
 (provide 'guix-ui-package)

emacs/guix-ui.el

@@ -47,6 +47,13 @@ generations in 'list' and 'info' buffers.")
 (guix-buffer-define-current-args-accessors
  "guix-ui-current" "profile" "search-type" "search-values")
 
+(defun guix-ui-read-profile ()
+  "Return `guix-current-profile' or prompt for it.
+This function is intended for using in `interactive' forms."
+  (if current-prefix-arg
+      (guix-profile-prompt)
+    guix-current-profile))
+
 (defun guix-ui-get-entries (profile entry-type search-type search-values
                                     &optional params)
   "Receive ENTRY-TYPE entries for PROFILE.