;;; FASL 
;;;
;;; A fasl object is a header followed by one or more objects followed by an
;;; end-of-fasl marker
;;;
;;; The header is the string "#@IK01"
;;; The end of fasl marker is "@"
;;;
;;; An object is either:
;;;   "N" : denoting the empty list
;;;   "T" : denoting #t
;;;   "F" : denoting #f
;;;   "E" : denoting the end of file object
;;;   "U" : denoting the unspecified value
;;;   "I" + 4-bytes : denoting a fixnum (in host byte order)
;;;   "C" + 1-byte : denoting a character
;;;   "P" + object1 + object2 : a pair
;;;   "V" + 4-bytes(n) + object ... : a vector of length n followed by n
;;;                                   objects
;;;   "S" + 4-bytes(n) + char ... : a string
;;;   "M" + symbol-name : a symbol
;;;   "G" + pretty-name + unique-name : a gensym
;;;   "R" + rtd-name + rtd-symbol + field-count + field-names
;;;   "{" + field-count + rtd + fields
;;;   ">" + 4-bytes(i) : mark the next object with index i
;;;   "<" + 4-bytes(i) : dereference the object marked with index i
;;;   "x" : denotes code
;;;   "T" : Thunk; followed by code.


(let ()
  (define write-fixnum 
    (lambda (x p)
      (unless (fixnum? x) (error 'write-fixnum "not a fixnum ~s" x))
      (write-char (integer->char (fxsll (fxlogand x #x3F) 2)) p)
      (write-char (integer->char (fxlogand (fxsra x 6) #xFF)) p)
      (write-char (integer->char (fxlogand (fxsra x 14) #xFF)) p)
      (write-char (integer->char (fxlogand (fxsra x 22) #xFF)) p)))
  (define write-int 
    (lambda (x p)
      (unless (fixnum? x) (error 'write-int "not a fixnum ~s" x))
      (write-char (integer->char (fxlogand x #xFF)) p)
      (write-char (integer->char (fxlogand (fxsra x 8) #xFF)) p)
      (write-char (integer->char (fxlogand (fxsra x 16) #xFF)) p)
      (write-char (integer->char (fxlogand (fxsra x 24) #xFF)) p)))

  (define fasl-write-immediate
    (lambda (x p)
      (cond
        [(null? x) (write-char #\N p)]
        [(fixnum? x) 
         (write-char #\I p)
         (write-fixnum x p)]
        [(char? x)
         (write-char #\C p)
         (write-char x p)]
        [(boolean? x)
         (write-char (if x #\T #\F) p)]
        [(eof-object? x) (write-char #\E p)]
        [(eq? x (void)) (write-char #\U p)]
        [else (error 'fasl-write "~s is not a fasl-writable immediate" x)])))

  (define do-write
    (lambda (x p h m)
      (cond
        [(pair? x)   
         (write-char #\P p)
         (fasl-write (cdr x) p h
           (fasl-write (car x) p h m))]
        [(vector? x)
         (write-char #\V p)
         (write-int (vector-length x) p)
         (let f ([x x] [i 0] [n (vector-length x)] [m m])
           (cond
             [(fx= i n) m]
             [else
              (f x (fxadd1 i) n
                 (fasl-write (vector-ref x i) p h m))]))]
        [(string? x) 
         (write-char #\S p)
         (write-int (string-length x) p)
         (let f ([x x] [i 0] [n (string-length x)])
           (cond
             [(fx= i n) m]
             [else
              (write-char (string-ref x i) p)
              (f x (fxadd1 i) n)]))]
        [(gensym? x)
         (write-char #\G p)
         (fasl-write (gensym->unique-string x) p h
           (fasl-write (symbol->string x) p h m))]
        [(symbol? x) 
         (write-char #\M p)
         (fasl-write (symbol->string x) p h m)]
        [(code? x)
         (write-char #\x p)
         (write-int (code-size x) p)
         (write-fixnum (code-freevars x) p)
         (let f ([i 0] [n (code-size x)])
           (unless (fx= i n)
             (write-char (integer->char (code-ref x i)) p)
             (f (fxadd1 i) n)))
         (fasl-write (code-reloc-vector x) p h m)]
        [(record? x)
         (let ([rtd (record-type-descriptor x)])
           (cond
             [(eq? rtd #%$base-rtd)
              ;;; rtd record
              (write-char #\R p)
              (let ([names (record-type-field-names x)]
                    [m 
                     (fasl-write (record-type-symbol x) p h
                       (fasl-write (record-type-name x) p h m))])
                (write-int (length names) p)
                (let f ([names names] [m m])
                  (cond
                    [(null? names) m]
                    [else
                     (f (cdr names)
                        (fasl-write (car names) p h m))])))]
             [else
              ;;; non-rtd record
              (write-char #\{ p)
              (write-int (length (record-type-field-names rtd)) p)
              (let f ([names (record-type-field-names rtd)] 
                      [m (fasl-write rtd p h m)])
                (cond
                  [(null? names) m]
                  [else
                   (f (cdr names) 
                      (fasl-write 
                         ((record-field-accessor rtd (car names)) x)
                         p h m))]))]))]
        [(procedure? x)
         (write-char #\Q p)
         (fasl-write ($closure-code x) p h m)]
        [else (error 'fasl-write "~s is not fasl-writable" x)])))
  (define fasl-write 
    (lambda (x p h m)
      (cond
        [(immediate? x) (fasl-write-immediate x p) m]
        [(get-hash-table h x #f) =>
         (lambda (mark)
           (unless (fixnum? mark)
             (error 'fasl-write "BUG: invalid mark ~s" mark))
           (cond
             [(fx= mark 0) ; singly referenced
              (do-write x p h m)]
             [(fx> mark 0) ; marked but not written
              (put-hash-table! h x (fx- 0 m))
              (write-char #\> p)
              (write-int m p)
              (do-write x p h (fxadd1 m))]
             [else
              (write-char #\< p)
              (write-int (fx- 0 mark) p)
              m]))]
        [else (error 'fasl-write "BUG: not in hash table ~s" x)]))) 
  (define make-graph
    (lambda (x h)
      (unless (immediate? x)
        (cond
          [(get-hash-table h x #f) =>
           (lambda (i) 
             (put-hash-table! h x (fxadd1 i)))]
          [else
           (put-hash-table! h x 0)
           (cond
             [(pair? x) 
              (make-graph (car x) h)
              (make-graph (cdr x) h)]
             [(vector? x)
              (let f ([x x] [i 0] [n (vector-length x)])
                (unless (fx= i n) 
                  (make-graph (vector-ref x i) h)
                  (f x (fxadd1 i) n)))]
             [(symbol? x) 
              (make-graph (symbol->string x) h)
              (when (gensym? x) (make-graph (gensym->unique-string x) h))]
             [(string? x) (void)]
             [(code? x) 
              (make-graph (code-reloc-vector x) h)]
             [(record? x)
              (when (eq? x #%$base-rtd) 
                (error 'fasl-write "$base-rtd is not writable"))
              (let ([rtd (record-type-descriptor x)])
                (cond
                  [(eq? rtd #%$base-rtd)
                   ;;; this is an rtd
                   (make-graph (record-type-name x) h)
                   (make-graph (record-type-symbol x) h)
                   (for-each (lambda (x) (make-graph x h))
                     (record-type-field-names x))]
                  [else
                   ;;; this is a record
                   (make-graph rtd h)
                   (for-each 
                     (lambda (name) 
                       (make-graph ((record-field-accessor rtd name) x) h))
                     (record-type-field-names rtd))]))]
             [(procedure? x)
              (let ([code ($closure-code x)])
                (unless (fxzero? ($code-freevars code))
                  (error 'fasl-write
                         "Cannot write a non-thunk procedure; the one given has ~s free vars"
                         ($code-freevars code)))
                (make-graph code h))]
             [else (error 'fasl-write "~s is not fasl-writable" x)])]))))
  (define do-fasl-write 
    (lambda (x port)
      (let ([h (make-hash-table)])
         (make-graph x h)
         (write-char #\# port)
         (write-char #\@ port)
         (write-char #\I port)
         (write-char #\K port)
         (write-char #\0 port)
         (write-char #\1 port)
         (fasl-write x port h 1))))
  (primitive-set! 'fasl-write
     (case-lambda 
       [(x) (do-fasl-write x (current-output-port))]
       [(x port)
        (unless (output-port? port)
          (error 'fasl-write "~s is not an output port" port))
        (do-fasl-write x port)])))