;;; -*- lexical-binding: t -*-
;;
;; this file:
;;   https://dataswamp.org/~incal/emacs-init/case.el

(defun upcase-p (char)
  (and (numberp char)
       (<= ?A char)
       (<=    char ?Z) ))

(defun downcase-p (char)
  (and (numberp char)
       (<= ?a char)
       (<=    char ?z) ))

(defun ucase (beg end)
  (interactive
   (if (region-active-p)
       (list (region-beginning) (region-end))
     (list (point) (+ (point) (or (and (listp current-prefix-arg)
                                       (car current-prefix-arg) )
                                  current-prefix-arg
                                  1) ))))
  (upcase-region beg end) )

(defun ccase (beg end)
  (let*((str   (buffer-substring-no-properties beg end))
        (chars (string-to-list str))
        (new) )
    (dolist (c chars)
      (push (cond ((upcase-p   c) (downcase c))
                  ((downcase-p c) (upcase   c))
                  (t c) ) new))
    (delete-region beg end)
    (dolist (c (nreverse new))
      (insert c) )))

(provide 'case)