Add version-compare and version>? to utils.scm.

* guix/utils.scm (version-compare, version>?): New exported procedures,
  based on version-string>?, which was formerly in gnu-maintenance.scm.

* guix/gnu-maintenance.scm (version-string>?): Removed procedure.
  (latest-release): Use 'version>?' instead of 'version-string>?'.

guix/gnu-maintenance.scm

@@ -28,6 +28,7 @@
   #:use-module (srfi srfi-26)
   #:use-module (system foreign)
   #:use-module (guix ftp-client)
+  #:use-module (guix utils)
   #:export (official-gnu-packages
             releases
             latest-release
@@ -156,21 +157,12 @@ pairs.  Example: (\"mit-scheme-9.0.1\" . \"/gnu/mit-scheme/stable.pkg/9.0.1\").
                                files)
                    result)))))))
 
-(define version-string>?
-  (let ((strverscmp
-         (let ((sym (or (dynamic-func "strverscmp" (dynamic-link))
-                        (error "could not find `strverscmp' (from GNU libc)"))))
-           (pointer->procedure int sym (list '* '*)))))
-    (lambda (a b)
-      "Return #t when B denotes a newer version than A."
-      (> (strverscmp (string->pointer a) (string->pointer b)) 0))))
-
 (define (latest-release project)
   "Return (\"FOO-X.Y\" . \"/bar/foo\") or #f."
   (let ((releases (releases project)))
     (and (not (null? releases))
          (fold (lambda (release latest)
-                 (if (version-string>? (car release) (car latest))
+                 (if (version>? (car release) (car latest))
                      release
                      latest))
                '("" . "")

guix/utils.scm

@@ -57,6 +57,8 @@
 
             gnu-triplet->nix-system
             %current-system
+            version-compare
+            version>?
             package-name->name+version))
 
 
@@ -422,6 +424,24 @@ returned by `config.guess'."
   ;; By default, this is equal to (gnu-triplet->nix-system %host-type).
   (make-parameter %system))
 
+(define version-compare
+  (let ((strverscmp
+         (let ((sym (or (dynamic-func "strverscmp" (dynamic-link))
+                        (error "could not find `strverscmp' (from GNU libc)"))))
+           (pointer->procedure int sym (list '* '*)))))
+    (lambda (a b)
+      "Return '> when A denotes a newer version than B,
+'< when A denotes a older version than B,
+or '= when they denote equal versions."
+      (let ((result (strverscmp (string->pointer a) (string->pointer b))))
+        (cond ((positive? result) '>)
+              ((negative? result) '<)
+              (else '=))))))
+
+(define (version>? a b)
+  "Return #t when A denotes a newer version than B."
+  (eq? '> (version-compare a b)))
+
 (define (package-name->name+version name)
   "Given NAME, a package name like \"foo-0.9.1b\", return two values:
 \"foo\" and \"0.9.1b\".  When the version part is unavailable, NAME and