;;; shm-evaporate.el --- Evaporating overlays
;; Copyright (c) 2014 Chris Done. All rights reserved.
;; This file 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, or (at your option)
;; any later version.
;; This file 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:
;; Support for evaporating pieces of code.
;;; Code:
(defface shm-evaporate-face
'((((class color)) :foreground "#666666"))
"Face for text that will evaporate when modified/overwritten."
:group 'shm-evaporate)
(defun shm-evaporate (beg end)
"Make the region evaporate when typed over."
(interactive "r")
(let ((o (make-overlay beg end nil nil nil)))
(overlay-put o 'shm-evaporate-overlay t)
(overlay-put o 'face 'shm-evaporate-face)
(overlay-put o 'shm-evaporate t)
(overlay-put o 'priority 2)
(overlay-put o 'modification-hooks '(shm-evaporate-modification-hook))
(overlay-put o 'insert-in-front-hooks '(shm-evaporate-insert-before-hook))))
(defun shm-evaporate-modification-hook (o changed beg end &optional len)
"Remove the overlay after a modification occurs."
(let ((inhibit-modification-hooks t))
(when (and changed
(overlay-start o))
(shm-evaporate-delete-text o beg end)
(delete-overlay o))))
(defun shm-evaporate-insert-before-hook (o changed beg end &optional len)
"Remove the overlay before inserting something at the start."
(let ((inhibit-modification-hooks t))
(when (and (not changed)
(overlay-start o))
(shm-evaporate-delete-text o beg end)
(delete-overlay o))))
(defun shm-evaporate-delete-text (o beg end)
"Delete the text associated with the evaporating slot."
(unless (eq this-command 'undo)
(delete-region (overlay-start o)
(overlay-end o))))
(provide 'shm-evaporate)
;;; shm-evaporate.el ends here