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+;;;; base.scm - Cuirass base module
+;;;
+;;; Copyright © 2012, 2016 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of Cuirass.
+;;;
+;;; Cuirass 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.
+;;;
+;;; Cuirass 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 Cuirass.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (cuirass base)
+  #:use-module (ice-9 format)
+  #:use-module (srfi srfi-19)
+  #:export (guix-variable
+            with-directory-excursion
+            call-with-time-display))
+
+(define (guix-variable module name)
+  "Dynamically link variable NAME under Guix module MODULE and return it.
+Note: this is used instead of `@', because when using `@' in an uncompiled
+file, Guile tries to load the module directly as it reads the source, which
+fails in our case, leading to the creation of empty (guix ...) modules."
+  (let ((m (resolve-interface `(guix ,module))))
+    (module-ref m name)))
+
+(define-syntax-rule (with-directory-excursion dir body ...)
+  "Run BODY with DIR as the process's current directory."
+  (let ((init (getcwd)))
+    (dynamic-wind
+      (lambda ()
+        (chdir dir))
+      (lambda ()
+        body ...)
+      (lambda ()
+        (chdir init)))))
+
+(define (call-with-time thunk kont)
+  "Call THUNK and pass KONT the elapsed time followed by THUNK's return
+values."
+  (let* ((start  (current-time time-monotonic))
+         (result (call-with-values thunk list))
+         (end    (current-time time-monotonic)))
+    (apply kont (time-difference end start) result)))
+
+(define (call-with-time-display thunk)
+  "Call THUNK and write to the current output port its duration."
+  (call-with-time thunk
+    (lambda (time . results)
+      (format #t "~,3f seconds~%"
+              (+ (time-second time)
+                 (/ (time-nanosecond time) 1e9)))
+      (apply values results))))