A minor mode to highlight the current scope in Lisp-like languages. Doesn't handle strings very well at the moment, but that's in the works.

parscope.el

;;; parscope-mode.el --- Minor mode for showing the current scope in Lisp-like languages.

;; Copyright (C) 2013 Nick Pascucci

;; Author: Nick Pascucci
;; Created: 22 Jun 2013
;; Keywords: tools
;; Version: 0.1
;; URL: https://gist.github.com/nickpascucci/5842987

;; This program 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.
;;
;; This program 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 Emacs; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.

;;; Commentary:

;; Inspired by https://www.youtube.com/watch?feature=player_embedded&v=wBl0rYXQdGg

;;; Code:

(defvar-local ps-overlay nil "Overlay highlighting the current scope.")

(define-minor-mode parscope-mode
  "Minor mode that highlights the current sexp."
  nil "ParScope" nil
  (ps/enable-disable))

(defface parscope-overlay-face
  '((default :background "#07272D"))
  "Face used to highlight the current scope."
  :group 'parscope)

(defun ps/enable-disable ()
  (if parscope-mode
      (ps/init)
    (ps/detach-hooks)
    (delete-overlay ps-overlay)))

(defun ps/init ()
  (when (not (null ps-overlay))
    (delete-overlay ps-overlay))
  (setq ps-overlay (make-overlay 3 3 (current-buffer)))
  (overlay-put ps-overlay 'face 'ps-overlay-face)
  (ps/set-scope-overlay)
  (ps/attach-hooks))

(defun ps/set-scope-overlay ()
  (interactive)
  (condition-case nil
    (save-excursion
      (backward-up-list)
      (let ((start (point)))
        (forward-sexp)
        (move-overlay ps-overlay start (point))
        (list start (point))))
    (error
     (move-overlay ps-overlay (point) (point)))))

(defun ps/update-scope ()
  (when parscope-mode
   (ps/set-scope-overlay)))

(defun ps/attach-hooks ()
  (add-hook 'post-command-hook #'ps/update-scope nil t))

(defun ps/detach-hooks ()
  (remove-hook 'post-command-hook #'ps/update-scope t))

I'm interested in adding this to MELPA. How about promoting it to a full repository so it has a more stable home and can receive pull requests (e.g. for the missing trailing ;;; parscope.el ends here line and autoload cookies)?

-Steve

P.S. To solve the string problem, you probably want to either use paredit's functions if available, or use a fix like this one: https://github.com/purcell/emacs.d/blob/master/init-editing-utils.el#L225

Sure thing, I'll migrate it to its own repo tonight. An updated version is up on Marmalade: http://marmalade-repo.org/packages/parscope, but I'd love to have it on more repos!

I'll definitely take a look at those string utils as well.

Full repo here: https://github.com/nickpascucci/ParScope