+;;; Dispatch on major mode.
+
+;; Two parts:
+;; - first define a specializer (derived-mode <mode>) to match symbols
+;; representing major modes, while obeying the major mode hierarchy.
+;; - then define a context-rewriter so you can write
+;; "&context (major-mode c-mode)" rather than
+;; "&context (major-mode (derived-mode c-mode))".
+
+(defun cl--generic-derived-specializers (mode &rest _)
+ ;; FIXME: Handle (derived-mode <mode1> ... <modeN>)
+ (let ((specializers ()))
+ (while mode
+ (push `(derived-mode ,mode) specializers)
+ (setq mode (get mode 'derived-mode-parent)))
+ (nreverse specializers)))
+
+(cl-generic-define-generalizer cl--generic-derived-generalizer
+ 90 (lambda (name) `(and (symbolp ,name) (functionp ,name) ,name))
+ #'cl--generic-derived-specializers)
+
+(cl-defmethod cl-generic-generalizers ((_specializer (head derived-mode)))
+ "Support for (derived-mode MODE) specializers.
+Used internally for the (major-mode MODE) context specializers."
+ (list cl--generic-derived-generalizer))
+
+(cl-generic-define-context-rewriter major-mode (mode &rest modes)
+ `(major-mode ,(if (consp mode)
+ ;;E.g. could be (eql ...)
+ (progn (cl-assert (null modes)) mode)
+ `(derived-mode ,mode . ,modes))))
+