snake-case/camel-case elisp functions

enake-camel.el

;; Usage:
;;
;; (defun snake-camel () (interactive)(kill-new(upcase-first(snake-to-camel(car kill-ring)))))
;; (defun camel-snake () (interactive)(kill-new(upcase(camel-to-snake(car kill-ring)))))

(defun snake-to-camel (s)
  ""
  (setq s (downcase s))
  (if (string-match "_" s)
      (concat (let ((fs (substring s 0 (match-beginning 0))))
                (concat (upcase (substring fs 0 1)) (substring fs 1 (length fs))))
              (snake-to-camel (substring s (match-end 0) (length s))))
    (concat (upcase (substring s 0 1)) (substring s 1 (length s)))))

(defun camel-to-snake (s)
  ""
  (save-match-data
    (let ((case-fold-search nil))
      (camel-to-snake-recursively s))))

(defun camel-to-snake-recursively (s)
  ""
  (let ((ss (downcase-first s)))
    (if (string-match "[A-Z]" ss)
        (concat (substring ss 0 (match-beginning 0)) "_" (camel-to-snake-recursively (substring ss (match-beginning 0) (length ss))))
      ss)))

(defun upcase-first (s)
  ""
  (concat
   (upcase (substring s 0 1))
   (substring s 1 (length s))))

(defun downcase-first (s)
  ""
  (concat
   (downcase (substring s 0 1))
   (substring s 1 (length s))))