add &optional n in last

Author: knorth55

lisp/l/common.l

@@ -448,9 +448,10 @@ if pos is bigger than the length of list, item is nconc'ed at the tail"
      (nconc result1 result2)))
 
 (defun rotate-list (l) (append (cdr l) (list (car l))))
-(defun last (x)
-  (while (consp (cdr x)) (setq x (cdr x)))
-  x)
+(defun last (x &optional (n 1))
+  (unless (integerp n)
+    (error "last &optional n must be integer"))
+  (nthcdr (max (- (length x) n) 0) x))
 (defun copy-tree (x) (subst t t x))
 (defun copy-list (x) (nreverse (reverse x)))
 (defun nreconc (x y) (nconc (nreverse x) y))