change viper to use derived-mode-p

* lisp/subr.el (provided-mode-derived-p): New function.
(derived-mode-p): Use it.
* lisp/emulation/viper.el (viper-mode): Use derived-mode-p.
(this-major-mode-requires-vi-state): Use provided-mode-derived-p.
(set-viper-state-in-major-mode): Use derived-mode-p.

1 files changed, 9 insertions, 4 deletions

diff --git a/lisp/subr.el b/lisp/subr.el
index 6b0403890cf..13567d8753e 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -1872,13 +1872,18 @@ Only affects hooks run in the current buffer."
 
 ;; PUBLIC: find if the current mode derives from another.
 
+(defun provided-mode-derived-p (mode &rest modes)
+  "Non-nil if MODE is derived from one of MODES.
+Uses the `derived-mode-parent' property of the symbol to trace backwards.
+If you just want to check `major-mode', use `derived-mode-p'."
+  (while (and (not (memq mode modes))
+              (setq mode (get mode 'derived-mode-parent))))
+  mode)
+
 (defun derived-mode-p (&rest modes)
   "Non-nil if the current major mode is derived from one of MODES.
 Uses the `derived-mode-parent' property of the symbol to trace backwards."
-  (let ((parent major-mode))
-    (while (and (not (memq parent modes))
-		(setq parent (get parent 'derived-mode-parent))))
-    parent))
+  (apply #'provided-mode-derived-p major-mode modes))
 
 ;;;; Minor modes.