emacs: Add development utils.

* emacs/guix-guile.el (guix-guile-current-module): New function.
* emacs/guix-devel.el: New file.
* emacs.am (ELFILES): Add it.
* doc/emacs.texi (Emacs Development): New node.
  (Emacs Interface): Add it.
* doc/contributing.texi (The Perfect Setup): Mention it.
* doc/guix.texi (Top): Add it.
* emacs/guix-init.el: Add 'guix-devel-activate-mode-maybe' to
  'scheme-mode-hook'.

emacs/guix-devel.el

@@ -0,0 +1,96 @@
+;;; guix-devel.el --- Development tools   -*- lexical-binding: t -*-
+
+;; Copyright © 2015 Alex Kost <alezost@gmail.com>
+
+;; 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This file provides commands useful for developing Guix (or even
+;; arbitrary Guile code) with Geiser.
+
+;;; Code:
+
+(require 'guix-guile)
+(require 'guix-geiser)
+(require 'guix-utils)
+
+(defgroup guix-devel nil
+  "Settings for Guix development utils."
+  :group 'guix)
+
+(defcustom guix-devel-activate-mode t
+  "If non-nil, then `guix-devel-mode' is automatically activated
+in Scheme buffers."
+  :type 'boolean
+  :group 'guix-devel)
+
+(defun guix-devel-use-modules (&rest modules)
+  "Use guile MODULES."
+  (apply #'guix-geiser-call "use-modules" modules))
+
+(defun guix-devel-use-module (&optional module)
+  "Use guile MODULE in the current Geiser REPL.
+MODULE is a string with the module name - e.g., \"(ice-9 match)\".
+Interactively, use the module defined by the current scheme file."
+  (interactive (list (guix-guile-current-module)))
+  (guix-devel-use-modules module)
+  (message "Using %s module." module))
+
+(defun guix-devel-copy-module-as-kill ()
+  "Put the name of the current guile module into `kill-ring'."
+  (interactive)
+  (guix-copy-as-kill (guix-guile-current-module)))
+
+(defvar guix-devel-keys-map
+  (let ((map (make-sparse-keymap)))
+    (define-key map (kbd "k") 'guix-devel-copy-module-as-kill)
+    (define-key map (kbd "u") 'guix-devel-use-module)
+    map)
+  "Keymap with subkeys for `guix-devel-mode-map'.")
+
+(defvar guix-devel-mode-map
+  (let ((map (make-sparse-keymap)))
+    (define-key map (kbd "C-c .") guix-devel-keys-map)
+    map)
+  "Keymap for `guix-devel-mode'.")
+
+;;;###autoload
+(define-minor-mode guix-devel-mode
+  "Minor mode for `scheme-mode' buffers.
+
+With a prefix argument ARG, enable the mode if ARG is positive,
+and disable it otherwise.  If called from Lisp, enable the mode
+if ARG is omitted or nil.
+
+When Guix Devel mode is enabled, it provides the following key
+bindings:
+
+\\{guix-devel-mode-map}"
+  :init-value nil
+  :lighter " Guix"
+  :keymap guix-devel-mode-map)
+
+;;;###autoload
+(defun guix-devel-activate-mode-maybe ()
+  "Activate `guix-devel-mode' depending on
+`guix-devel-activate-mode' variable."
+  (when guix-devel-activate-mode
+    (guix-devel-mode)))
+
+(provide 'guix-devel)
+
+;;; guix-devel.el ends here

emacs/guix-guile.el

@@ -24,6 +24,19 @@
 
 ;;; Code:
 
+(require 'geiser-guile)
+
+(defun guix-guile-current-module ()
+  "Return a string with the current guile module.
+Return nil, if current buffer does not define a module."
+  ;; Modified version of `geiser-guile--get-module'.
+  (save-excursion
+    (geiser-syntax--pop-to-top)
+    (when (or (re-search-backward geiser-guile--module-re nil t)
+              (looking-at geiser-guile--library-re)
+              (re-search-forward geiser-guile--module-re nil t))
+      (match-string-no-properties 1))))
+
 (defun guix-guile-make-call-expression (proc &rest args)
   "Return \"(PROC ARGS ...)\" string.
 PROC and ARGS should be strings."

emacs/guix-init.el

@@ -12,4 +12,6 @@ avoid loading autoloads of Emacs packages installed in
   (require 'guix-emacs)
   (guix-emacs-load-autoloads 'all))
 
+(add-hook 'scheme-mode-hook 'guix-devel-activate-mode-maybe)
+
 (provide 'guix-init)