;; BF Lexer in Scheme
;; Jon Simons (simonsj at ccs dot neu dot edu)
;; August, 2007
;; -------------------------------------------------------------------------
(module bf-lex mzscheme
  
  (require scheme/list)
  
  (provide lex)
  
  ;; Is the given character a valid BF token?
  ;;
  ;; valid-token? : character -> boolean
  (define (valid-token? c)
    (ormap
     (lambda (x) (char=? c x))
     (list #\- #\+ #\> #\< #\[ #\] #\, #\.)))
  
  ;; Lexes a BF source file, returning a list of character tokens.
  ;;
  ;; TODO: Some kind of token-mapping so that we can parse Ook!
  ;;       and feckfeck dialects?
  ;;       Make my own dialect!
  ;;
  ;; lex : string -> (list of characters)
  (define (lex input)
    (letrec ((read-to-list (lambda (lst)
                             (let ((c (read-char)))
                               (if (eof-object? c)
                                   lst
                                   (if (valid-token? c)
                                       (read-to-list (cons c lst))
                                       (read-to-list lst))))))
             (get-input-vector (lambda ()
                                 (reverse (read-to-list ())))))
      (with-input-from-file input get-input-vector)))
  )