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+;;;; elib-node.el,v 1.2 1992/04/07 20:49:16 berliner Exp
+;;;; This file implements the nodes used in binary trees and
+;;;; doubly linked lists
+;;;;
+;;;; Copyright (C) 1991 Inge Wallin
+;;;;
+;;;; This file is part of the GNU Emacs lisp library, Elib.
+;;;;
+;;;; GNU Elib 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 1, or (at your option)
+;;;; any later version.
+;;;;
+;;;; GNU Elib 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, 675 Mass Ave, Cambridge, MA 02139, USA.
+;;;; 
+;;;; Author: Inge Wallin
+;;;; 
+
+;;;
+;;; A node is implemented as an array with three elements, using
+;;; (elt node 0) as the left pointer
+;;; (elt node 1) as the right pointer
+;;; (elt node 2) as the data
+;;;
+;;; Some types of trees, e.g. AVL trees, need bigger nodes, but 
+;;; as long as the first three parts are the left pointer, the 
+;;; right pointer and the data field, these macros can be used.
+;;;
+
+
+(provide 'elib-node)
+
+
+(defmacro elib-node-create (left right data)
+  "Create a tree node from LEFT, RIGHT and DATA."
+  (` (vector (, left) (, right) (, data))))
+
+
+(defmacro elib-node-left (node)
+  "Return the left pointer of NODE."
+  (` (aref (, node) 0)))
+
+
+(defmacro elib-node-right (node)
+  "Return the right pointer of NODE."
+  (` (aref (, node) 1)))
+
+
+(defmacro elib-node-data (node)
+  "Return the data of NODE."
+  (` (aref (, node) 2)))
+
+
+(defmacro elib-node-set-left (node newleft)
+  "Set the left pointer of NODE to NEWLEFT."
+  (` (aset (, node) 0 (, newleft))))
+
+
+(defmacro elib-node-set-right (node newright)
+  "Set the right pointer of NODE to NEWRIGHT."
+  (` (aset (, node) 1 (, newright))))
+
+
+(defmacro elib-node-set-data (node newdata)
+  "Set the data of NODE to NEWDATA."
+  (` (aset (, node) 2 (, newdata))))
+
+
+
+(defmacro elib-node-branch (node branch)
+  "Get value of a branch of a node.
+NODE is the node, and BRANCH is the branch.
+0 for left pointer, 1 for right pointer and 2 for the data."
+  (` (aref (, node) (, branch))))
+
+
+(defmacro elib-node-set-branch (node branch newval)
+  "Set value of a branch of a node.
+NODE is the node, and BRANCH is the branch.
+0 for left pointer, 1 for the right pointer and 2 for the data.
+NEWVAL is new value of the branch."
+  (` (aset (, node) (, branch) (, newval))))