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;;; rswitcher.el --- Structure and functions for switching elements -*- lexical-binding: t; -*-
;; Copyright (C) 2012-2013 Damien Cassou
;; Author: Damien Cassou <>
;; GIT:
;; Created: 2012-06-27
;; Keywords: emacs package elisp switcher
;; This file is NOT part of GNU Emacs.
;; 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 2, 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
;; General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with this program ; see the file COPYING. If not, write to
;; the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.
;; Install
;; Please see the file from the same distribution
;;; Commentary:
;; This code provides a data structure and functions to mimic ALT+TAB
;; behavior of window managers within Emacs and with Emacs feeling.
;; `rswitcher-switch-full' is similar to the initial ALT+TAB while
;; `rswitcher-switch-partial' is similar to subsequent TABs.
;;; Code:
(defun rswitcher-make ()
"Return a new switcher.
The switcher is internally implemented as a cons. The `car' of
this cons contains the list of elements in the rswitcher (see
`rswitcher--elements') while its `cdr' contains the index of the
most-recent element (see `rswitcher--last-pos')."
(cons nil nil))
(defun rswitcher--elements (switcher)
"Return the list of elements in SWITCHER.
See `rswitcher-length', `rswitcher-empty-p', `rswitcher-memq',
`rswitcher-add', and `rswitcher-delete-most-recent' for ways to query
and manipulate SWITCHER."
(car switcher))
(defun rswitcher--last-pos (switcher)
"Return the index of SWITCHER's most-recent element.
A value of 0 means the first element of SWITCHER's elements. This
function returns nil in all cases except after a
`rswitcher-switch-partial' (and the function
`rswitcher--reset-last-pos' will make this function return nil
again). See `rswitcher--most-recent-pos' and
`rswitcher--most-recent' for higher-level functions. Change the
value returned by this function by using
`rswitcher--reset-last-pos', `rswitcher--increment-last-pos', and
(cdr switcher))
(defun rswitcher--set-last-pos (switcher last-pos)
"Set the last pos field of SWITCHER to be LAST-POS.
A value of 0 means the first element of SWITCHER's elements."
(setcdr switcher last-pos))
(defun rswitcher--increment-last-pos (switcher)
"Add 1 (modulo SWITCHER's number of elements) to LAST-POS field."
(let ((last-pos (rswitcher--last-pos switcher)))
(rswitcher--set-last-pos switcher
(% (1+ last-pos)
(rswitcher-length switcher)))))
(defun rswitcher--reset-last-pos (switcher)
"Set last pos field of SWITCHER to nil.
See `rswitcher--last-pos'."
(rswitcher--set-last-pos switcher nil))
(defun rswitcher-length (switcher)
"Return the number of elements in SWITCHER.
See `rswitcher--elements'."
(length (rswitcher--elements switcher)))
(defun rswitcher-empty-p (switcher)
"Check if there is no more elements in SWITCHER."
(zerop (rswitcher-length switcher)))
(defun rswitcher--most-recent-pos (switcher)
"Return the index of the most recent element.
The most recent element is always the first of SWITCHER's
elements (in which case the function returns 0) except after a
call to `rswitcher-switch-partial' in which case the most recent
element is pointed to by the last pos field of SWITCHER."
(or (rswitcher--last-pos switcher) 0))
(defun rswitcher-most-recent (switcher)
"Return the most recently accessed element in SWITCHER."
(elt (rswitcher--elements switcher) (rswitcher--most-recent-pos switcher)))
(defun rswitcher--push (switcher elt)
"Update SWITCHER's elements by adding ELT in front."
(unless (member elt (rswitcher--elements switcher))
(setcar switcher (cons elt (rswitcher--elements switcher)))))
(defun rswitcher-make-most-recent-elt-the-first (switcher)
"Move most recent element to the beginning of SWITCHER's elements."
(unless (zerop (rswitcher--most-recent-pos switcher))
(rswitcher--delete switcher (rswitcher--most-recent-pos switcher)))))
(defun rswitcher-add (switcher elt)
"Reorganize SWITCHER with most-recent element on front and push ELT."
(rswitcher-make-most-recent-elt-the-first switcher)
(rswitcher--push switcher elt)
(rswitcher--reset-last-pos switcher))
(defun rswitcher--pop (switcher)
"Remove and return the first element of SWITCHER's elements."
(let ((elements (rswitcher--elements switcher)))
(car elements)
(setcar switcher (cdr elements)))))
(defun rswitcher-memq (switcher elt)
"Check if SWITCHER's elements include ELT.
Comparison done with `eq'."
(memq elt (rswitcher--elements switcher)))
(defun rswitcher--delete (switcher pos)
"Delete and return the element in SWITCHER at position POS.
This function only accepts valid values for POS between 0 and the
number of SWITCHER's elements minus 1."
;; return the deleted element
(elt (rswitcher--elements switcher) pos)
(if (zerop pos)
(rswitcher--pop switcher)
(let ((tail (nthcdr (1+ pos) (rswitcher--elements switcher)))
(head (nthcdr (1- pos) (rswitcher--elements switcher))))
(setcdr head tail)))
(if (= pos (rswitcher--most-recent-pos switcher))
;; we just removed the element that was most-recent
(rswitcher--reset-last-pos switcher))))
(defun rswitcher-delete-all (switcher)
"Remove all elements from SWITCHER."
(while (not (rswitcher-empty-p switcher))
(rswitcher-delete-most-recent switcher)))
(defun rswitcher-delete-most-recent (switcher)
"Remove the most recent element from SWITCHER."
(rswitcher--delete switcher (rswitcher--most-recent-pos switcher)))
(defun rswitcher--swap-first-two-elts (switcher)
"Reorganize SWITCHER by swapping first and second elements."
(let ((first (rswitcher--pop switcher))
(new (rswitcher--pop switcher)))
(rswitcher--push switcher first)
(rswitcher--push switcher new)))
(defun rswitcher-switch-full (switcher)
"Select the next most recent element in SWITCHER.
This function is similar to pressing and releasing ALT+TAB in
standard window managers. Repeatedly calling this function will
always select the two most recent elements alternatively."
(when (>= (rswitcher-length switcher) 2)
(rswitcher-make-most-recent-elt-the-first switcher)
(rswitcher--swap-first-two-elts switcher)
(rswitcher--reset-last-pos switcher)))
(defun rswitcher-switch-partial (switcher)
"Continue switching after 1 full switch and many partial switches.
This function is similar to pressing TAB after pressing ALT+TAB.
Repeatedly calling this function will alternatively select all
elements of SWITCHER, most recent elements first."
(when (>= (rswitcher-length switcher) 2)
(if (rswitcher--last-pos switcher)
(rswitcher--increment-last-pos switcher)
;; Reverse swap done in previous execution of
;; `rswitcher-switch-full'
(rswitcher--swap-first-two-elts switcher)
(rswitcher--set-last-pos switcher
(if (> (rswitcher-length switcher) 2) 2 0)))))
(provide 'rswitcher)
;;; rswitcher.el ends here