rot13.lisp

#!/usr/bin/clisp

;;; ROT13 (rotate by 13 places) algorithm implemented Common Lisp

;;; Example:

;;   CL-USER> (rot13-string "HELLO") => "URYYB"
;; or
;;   [shell]$ echo 'HELLO' | clisp rot13.lisp

;;; Source: $EMACS/lisp/rot13.el

;;; Code:

(defvar *rot13-translate-table*
  (let ((str (make-string 127 :initial-element #\NUll)))
    (dotimes (i 127)
      (setf (elt str i) (code-char i)))
    (dotimes (i 26)
      (setf (elt str (+ i #1=#.(char-code #\a)))
            (code-char (+ (mod (+ i 13) 26) #1#)))
      (setf (elt str (+ i #2=#.(char-code #\A)))
            (code-char (+ (mod (+ i 13) 26) #2#))))
    str)
  "String table for ROT13 translation.")

(defun rot13-char (char)
  (handler-case 
      (elt *rot13-translate-table* (char-int char))
    (error (e) char)))

(defun rot13-string (string)
  (map 'string #'rot13-char string))

(defun main ()
  (loop for line = (read-line nil nil)
        while line
        do (format t "~A~%" (rot13-string line))))

(main)

;;; EOF