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+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix import utils)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 regex)
+  #:use-module (srfi srfi-1)
+  #:export (factorize-uri))
+
+(define (factorize-uri uri version)
+  "Factorize URI, a package tarball URI as a string, such that any occurrences
+of the string VERSION is replaced by the symbol 'version."
+  (let ((version-rx (make-regexp (regexp-quote version))))
+    (match (regexp-exec version-rx uri)
+      (#f
+       uri)
+      (_
+       (let ((indices (fold-matches version-rx uri
+                                    '((0))
+                                    (lambda (m result)
+                                      (match result
+                                        (((start) rest ...)
+                                         `((,(match:end m))
+                                           (,start . ,(match:start m))
+                                           ,@rest)))))))
+         (fold (lambda (index result)
+                 (match index
+                   ((start)
+                    (cons (substring uri start)
+                          result))
+                   ((start . end)
+                    (cons* (substring uri start end)
+                           'version
+                           result))))
+               '()
+               indices))))))