COMMENT ⊗   VALID 00002 PAGES
C REC  PAGE   DESCRIPTION
C00001 00001
C00002 00002	move.lsp[f81,jmc]	Routines for moving objects from pile to pile
C00004 ENDMK
C⊗;
;;;move.lsp[f81,jmc]	Routines for moving objects from pile to pile
;;; These routines move objects from one
;;; pile to another and (we hope) can be used for any kind of
;;; solitaire including games like nim and Tower of Hanoi or for
;;; the simulation of systems with movable physical objects.

;;; Our intent is that the piles are named by atoms, and the arguments
;;; x  and  y  are the names of the piles.

(defun move (xx yy n) ; moves  n  objects from pile  xx  to pile  yy
	(prog (z)
	      (if (lessp (length (eval xx)) n)
		  (return (list 'too_short xx)))
	      (setq z (iseg (eval xx) n))
	      (set xx (remove (eval xx) n))
	      (set yy (append z (eval yy)))
	      (return 'move_wins)
	      ))
;;; There will be bugs if  xx  and  yy  are used as names of piles.
;;; Perhaps many programs will use gensyms.
;
;;; The initial  n  elements of the list  u.
(defun iseg (u n) (if (= n 0) nil (cons (car u) (iseg (cdr u) (sub1 n)))))
;
;;; What's left of  u  after the initial  n  element are removed.
(defun remove (u n) (if (= n 0) u (remove (cdr u) (sub1 n))))