From 9f554133be83f06d5a3d0bfc713331e59eb2116c Mon Sep 17 00:00:00 2001
From: Chris Marusich <address@hidden>
Date: Tue, 12 Jul 2016 22:53:10 -0700
Subject: [PATCH 2/9] Refactor: extract procedure:
 relative-generation-spec->number

---
 guix/profiles.scm        | 16 ++++++++++++++++
 guix/scripts/package.scm |  7 +------
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/guix/profiles.scm b/guix/profiles.scm
index 38f69dd..3828d44 100644
--- a/guix/profiles.scm
+++ b/guix/profiles.scm
@@ -96,6 +96,7 @@
             generation-number
             generation-numbers
             profile-generations
+            relative-generation-spec->number
             relative-generation
             previous-generation-number
             generation-time
@@ -968,6 +969,21 @@ former profiles were found."
         '()
         generations)))
 
+(define (relative-generation-spec->number profile spec)
+  "Return PROFILE's generation specified by SPEC, which is a string.  The SPEC
+may be a N, -N, or +N, where N is a number.  If the spec is N, then the number
+returned is N.  If it is -N, then the number returned is the profile's current
+generation number minus N.  If it is +N, then the number returned is the
+profile's current generation number plus N.  Return #f if there is no such
+generation."
+  (let ((number (string->number spec)))
+    (and number
+         (case (string-ref spec 0)
+           ((#\+ #\-)
+            (relative-generation profile number))
+           (else number)))))
+
+
 (define* (relative-generation profile shift #:optional
                               (current (generation-number profile)))
   "Return PROFILE's generation shifted from the CURRENT generation by SHIFT.
diff --git a/guix/scripts/package.scm b/guix/scripts/package.scm
index b87aee0..1d8972c 100644
--- a/guix/scripts/package.scm
+++ b/guix/scripts/package.scm
@@ -774,12 +774,7 @@ processed, #f otherwise."
                                    #:key dry-run?)
   "Switch PROFILE to the generation specified by SPEC."
   (unless dry-run?
-    (let* ((number (string->number spec))
-           (number (and number
-                        (case (string-ref spec 0)
-                          ((#\+ #\-)
-                           (relative-generation profile number))
-                          (else number)))))
+    (let ((number (relative-generation-spec->number profile spec)))
       (if number
           (switch-to-generation* profile number)
           (leave (_ "cannot switch to generation '~a'~%") spec)))))
-- 
2.9.2