emacs/guix-history.el

   1 ;;; guix-history.el --- History of buffer information
   2
   3 ;; Copyright © 2014 Alex Kost <alezost@gmail.com>
   4
   5 ;; This file is part of GNU Guix.
   6
   7 ;; GNU Guix is free software; you can redistribute it and/or modify
   8 ;; it under the terms of the GNU General Public License as published by
   9 ;; the Free Software Foundation, either version 3 of the License, or
  10 ;; (at your option) any later version.
  11
  12 ;; GNU Guix is distributed in the hope that it will be useful,
  13 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 ;; GNU General Public License for more details.
  16
  17 ;; You should have received a copy of the GNU General Public License
  18 ;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
  19
  20 ;;; Commentary:
  21
  22 ;; This file provides support for history of buffers similar to the
  23 ;; history of a `help-mode' buffer.
  24
  25 ;;; Code:
  26
  27 (require 'cl-macs)
  28
  29 (defvar-local guix-history-stack-item nil
  30   "Current item of the history.
  31 A list of the form (FUNCTION [ARGS ...]).
  32 The item is used by calling (apply FUNCTION ARGS).")
  33 (put 'guix-history-stack-item 'permanent-local t)
  34
  35 (defvar-local guix-history-back-stack nil
  36   "Stack (list) of visited items.
  37 Each element of the list has a form of `guix-history-stack-item'.")
  38 (put 'guix-history-back-stack 'permanent-local t)
  39
  40 (defvar-local guix-history-forward-stack nil
  41   "Stack (list) of items visited with `guix-history-back'.
  42 Each element of the list has a form of `guix-history-stack-item'.")
  43 (put 'guix-history-forward-stack 'permanent-local t)
  44
  45 (defvar guix-history-size 0
  46   "Maximum number of items saved in history.
  47 If 0, the history is disabled.")
  48
  49 (defun guix-history-add (item)
  50   "Add ITEM to history."
  51   (and guix-history-stack-item
  52        (push guix-history-stack-item guix-history-back-stack))
  53   (setq guix-history-forward-stack nil
  54         guix-history-stack-item item)
  55   (when (>= (length guix-history-back-stack)
  56             guix-history-size)
  57     (setq guix-history-back-stack
  58           (cl-loop for elt in guix-history-back-stack
  59                    for i from 1 to guix-history-size
  60                    collect elt))))
  61
  62 (defun guix-history-replace (item)
  63   "Replace current item in history with ITEM."
  64   (setq guix-history-stack-item item))
  65
  66 (defun guix-history-goto (item)
  67   "Go to the ITEM of history.
  68 ITEM should have the form of `guix-history-stack-item'."
  69   (or (listp item)
  70       (error "Wrong value of history element"))
  71   (setq guix-history-stack-item item)
  72   (apply (car item) (cdr item)))
  73
  74 (defun guix-history-back ()
  75   "Go back to the previous element of history in the current buffer."
  76   (interactive)
  77   (or guix-history-back-stack
  78       (user-error "No previous element in history"))
  79   (push guix-history-stack-item guix-history-forward-stack)
  80   (guix-history-goto (pop guix-history-back-stack)))
  81
  82 (defun guix-history-forward ()
  83   "Go forward to the next element of history in the current buffer."
  84   (interactive)
  85   (or guix-history-forward-stack
  86       (user-error "No next element in history"))
  87   (push guix-history-stack-item guix-history-back-stack)
  88   (guix-history-goto (pop guix-history-forward-stack)))
  89
  90 (provide 'guix-history)
  91
  92 ;;; guix-history.el ends here