;; Copyright (C) 2007, Emilio C. Lopes <e@gmx.net>
;;
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.
;;
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;;
;; If you have not received a copy of the GNU General Public License
;; along with this software, it can be obtained from the GNU Project's
;; World Wide Web server (http://www.gnu.org/copyleft/gpl.html), from
;; its FTP server (ftp://ftp.gnu.org/pub/gnu/GPL), by sending an eletronic
;; mail to this program's maintainer or by writting to the Free Software
;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

(define r5rs-keywords '(cons car cdr define + - * / =  <= < > >= if lambda let ...))

(define (obfuscate-symbol symbol)
  ;; this code is Scsh specific.  Just use a hash algorith available
  ;; in your implementation.
  (string->symbol (string-append "x" (number->string (md5-digest->number (md5-digest-for-string (symbol->string symbol))) 16))))

(define (obfuscate expr)
  (cond
   ((and (symbol? expr)
         (not (memq expr r5rs-keywords)))
    (obfuscate-symbol expr))
   ((pair? expr)
    (cons (obfuscate (car expr)) (obfuscate (cdr expr))))
   (else
    expr)))

(obfuscate '(define (fac n)
              (if (<= n 1)
                  1
                  (* n (fac (- n 1))))))

;; => (define (xd2467530ef7303b14c9988df20bb8ce4 x7b8b965ad4bca0e41ab51de7b31363a1) (if (<= x7b8b965ad4bca0e41ab51de7b31363a1 1) 1 (* x7b8b965ad4bca0e41ab51de7b31363a1 (xd2467530ef7303b14c9988df20bb8ce4 (- x7b8b965ad4bca0e41ab51de7b31363a1 1)))))

;; (xd2467530ef7303b14c9988df20bb8ce4 5) => 120