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+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;
+;; Manipulate variations (which are really just lists of plies)
+;;
+;; $Revision$
+
+;;; Commentary:
+
+;; A chess variations is a simple list of plies.  This module provides
+;; an abstraction layer for applications.
+
+(require 'chess-ply)
+
+(defsubst chess-var-plies (var)
+  "Return the tags alist associated with VAR."
+  var)
+
+(defsubst chess-var-pos (var &optional index)
+  "Return the position related to VAR's INDEX position."
+  (chess-ply-pos (chess-var-ply var index)))
+
+(defsubst chess-var-index (var)
+  "Return the VAR's current position index."
+  (1- (length (chess-var-plies var))))
+
+(defsubst chess-var-seq (var)
+  "Return the current VAR sequence."
+  (1+ (/ (chess-var-index var) 2)))
+
+(defsubst chess-var-side-to-move (var)
+  (chess-pos-side-to-move (chess-var-pos var)))
+
+(defun chess-var-ply (var &optional index)
+  "Return the position related to VAR's INDEX position."
+  (if index
+      (nth index (chess-var-plies var))
+    (car (last (chess-var-plies var)))))
+
+(defun chess-var-add-ply (var ply)
+  "Return the position related to VAR's INDEX position."
+  (let ((plies (chess-var-plies var)))
+    (assert plies)
+    (nconc plies (list ply))))
+
+(defsubst chess-var-create (&optional position)
+  "Create a new chess variation object.
+Optionally use the given starting POSITION.
+SEARCH-FUNC specifies the function used to test the legality of moves.
+TAGS is the starting set of var tags (which can always be changed
+later using the various tag-related methods)."
+  (list (chess-ply-create (or position (chess-pos-create)))))
+
+(defun chess-var-move (var ply)
+  "Make a move in the current VAR, from FROM to TO.
+This creates a new position and adds it to the main variation.
+The 'changes' of the last ply reflect whether the var is currently in
+progress (nil), if it is drawn, resigned, mate, etc."
+  (let ((current-ply (chess-var-ply var))
+	(changes (chess-ply-changes ply))
+	(position (chess-ply-pos ply)))
+    (unless (equal position (chess-ply-pos current-ply))
+      (error "Positions do not match"))
+    (unless (chess-search-position
+	     position (cadr (chess-ply-changes ply))
+	     (chess-pos-piece position (car (chess-ply-changes ply))))
+      (signal 'chess-illegal "Illegal move"))
+    (chess-ply-set-changes current-ply changes)
+    (chess-var-add-ply var (chess-ply-create
+			    (chess-ply-next-pos current-ply)))))
+
+(provide 'chess-var)
+
+;;; chess-var.el ends here