;;; BrainFuck for Emacs

;; BrainFuck Example 1
;; @ を表示
;; >++++++[<++++++++++>-]<++++.

;; BrainFuck Example 2
;; @ を改行しつつ表示
;; >++++++[<++++++++++>-]<++++ >>+[<++++++++++>-]+++<.<.>.<..>.<...>.

;; BrainFuck Example 3
;; 入力した回数だけ @ を表示
;; >++++++[<++++++++++>-]<++++ >>,[<<.>>-]

;; BrainFuck Example 4
;; "Hello, World" を表示する
;; (let ((str "Hello, World"))
;;   (dotimes (i (length str))
;;     (insert (format "%d " (aref str i)))))
;; 72 101 108 108 111 44 32 87 111 114 108 100
;; >+++++++[<++++++++++>-]<++. >
;; >++++++++++[<++++++++++>-]<+. >
;; >+++++++++++[<++++++++++>-]<--.. >
;; >+++++++++++[<++++++++++>-]<+. >
;; >++++[<++++++++++>-]<++++. >
;; >+++[<++++++++++>-]<++. >
;; >+++++++++[<++++++++++>-]<---. >
;; >+++++++++++[<++++++++++>-]<+. >
;; >+++++++++++[<++++++++++>-]<++++. >
;; >+++++++++++[<++++++++++>-]<--. >
;; >++++++++++[<++++++++++>-]<. >

(defun bf (beg end)
  (interactive "r")
  (let ((src (buffer-substring-no-properties beg end)))
    (pop-to-buffer "*Brain Fuck*")
    (brainfuck-eval src)))

(defun brainfuck-eval (src)
  (let ((memory (make-vector 256 0))
	(ptr 0))
  (do ((i 0 (incf i))) ((>= i (length src)))
    (case (aref src i)
      (?< (decf ptr)) (?> (incf ptr))
      (?+ (incf (aref memory ptr)))
      (?- (decf (aref memory ptr))) 
      (?. (insert (aref memory ptr)))
      (?, (setf (aref memory ptr) (read)))
      (?\[ (when (eq (aref memory ptr) 0)
	     (let ((level 1))
	       (while (not (= level 0))
		 (incf i)
		 (case (aref src i)
		   (?\[ (incf level))
		   (?\] (decf level)))))))
      (?\] (when (not (eq (aref memory ptr) 0))
	     (let ((level 1))
	       (while (not (= level 0))
		 (decf i)
		 (case (aref src i)
		   (?\[ (decf level))
		   (?\] (incf level)))))))))))