[sbcl.git] / src / code / print.lisp

;;;; the printer

;;;; This software is part of the SBCL system. See the README file for
;;;; more information.
;;;;
;;;; This software is derived from the CMU CL system, which was
;;;; written at Carnegie Mellon University and released into the
;;;; public domain. The software is in the public domain and is
;;;; provided with absolutely no warranty. See the COPYING and CREDITS
;;;; files for more information.

(in-package "SB!IMPL")
\f
;;;; exported printer control variables

;;; FIXME: Many of these have nontrivial types, e.g. *PRINT-LEVEL*,
;;; *PRINT-LENGTH*, and *PRINT-LINES* are (OR NULL UNSIGNED-BYTE).

(defvar *print-readably* nil
  #!+sb-doc
  "If true, all objects will printed readably. If readable printing is
  impossible, an error will be signalled. This overrides the value of
  *PRINT-ESCAPE*.")
(defvar *print-escape* t
  #!+sb-doc
  "Should we print in a reasonably machine-readable way? (possibly
  overridden by *PRINT-READABLY*)")
(defvar *print-pretty* nil ; (set later when pretty-printer is initialized)
  #!+sb-doc
  "Should pretty printing be used?")
(defvar *print-base* 10.
  #!+sb-doc
  "the output base for RATIONALs (including integers)")
(defvar *print-radix* nil
  #!+sb-doc
  "Should base be verified when printing RATIONALs?")
(defvar *print-level* nil
  #!+sb-doc
  "How many levels should be printed before abbreviating with \"#\"?")
(defvar *print-length* nil
  #!+sb-doc
  "How many elements at any level should be printed before abbreviating
  with \"...\"?")
(defvar *print-circle* nil
  #!+sb-doc
  "Should we use #n= and #n# notation to preserve uniqueness in general (and
  circularity in particular) when printing?")
(defvar *print-case* :upcase
  #!+sb-doc
  "What case should the printer should use default?")
(defvar *print-array* t
  #!+sb-doc
  "Should the contents of arrays be printed?")
(defvar *print-gensym* t
  #!+sb-doc
  "Should #: prefixes be used when printing symbols with null SYMBOL-PACKAGE?")
(defvar *print-lines* nil
  #!+sb-doc
  "the maximum number of lines to print per object")
(defvar *print-right-margin* nil
  #!+sb-doc
  "the position of the right margin in ems (for pretty-printing)")
(defvar *print-miser-width* nil
  #!+sb-doc
  "If the remaining space between the current column and the right margin
   is less than this, then print using ``miser-style'' output. Miser
   style conditional newlines are turned on, and all indentations are
   turned off. If NIL, never use miser mode.")
(defvar *print-pprint-dispatch*)
#!+sb-doc
(setf (fdocumentation '*print-pprint-dispatch* 'variable)
      "the pprint-dispatch-table that controls how to pretty-print objects")

(defmacro with-standard-io-syntax (&body body)
  #!+sb-doc
  "Bind the reader and printer control variables to values that enable READ
   to reliably read the results of PRINT. These values are:
       *PACKAGE*                        the COMMON-LISP-USER package
       *PRINT-ARRAY*                    T
       *PRINT-BASE*                     10
       *PRINT-CASE*                     :UPCASE
       *PRINT-CIRCLE*                   NIL
       *PRINT-ESCAPE*                   T
       *PRINT-GENSYM*                   T
       *PRINT-LENGTH*                   NIL
       *PRINT-LEVEL*                    NIL
       *PRINT-LINES*                    NIL
       *PRINT-MISER-WIDTH*              NIL
       *PRINT-PRETTY*                   NIL
       *PRINT-RADIX*                    NIL
       *PRINT-READABLY*                 T
       *PRINT-RIGHT-MARGIN*             NIL
       *READ-BASE*                      10
       *READ-DEFAULT-FLOAT-FORMAT*      SINGLE-FLOAT
       *READ-EVAL*                      T
       *READ-SUPPRESS*                  NIL
       *READTABLE*                      the standard readtable"
  `(%with-standard-io-syntax (lambda () ,@body)))

(defun %with-standard-io-syntax (function)
  (declare (type function function))
  (let ((*package* (find-package "COMMON-LISP-USER"))
        (*print-array* t)
        (*print-base* 10)
        (*print-case* :upcase)
        (*print-circle* nil)
        (*print-escape* t)
        (*print-gensym* t)
        (*print-length* nil)
        (*print-level* nil)
        (*print-lines* nil)
        (*print-miser-width* nil)
        (*print-pretty* nil)
        (*print-radix* nil)
        (*print-readably* t)
        (*print-right-margin* nil)
        (*read-base* 10)
        (*read-default-float-format* 'single-float)
        (*read-eval* t)
        (*read-suppress* nil)
        ;; FIXME: It doesn't seem like a good idea to expose our
        ;; disaster-recovery *STANDARD-READTABLE* here. What if some
        ;; enterprising user corrupts the disaster-recovery readtable
        ;; by doing destructive readtable operations within
        ;; WITH-STANDARD-IO-SYNTAX? Perhaps we should do a
        ;; COPY-READTABLE? The consing would be unfortunate, though.
        (*readtable* *standard-readtable*))
    (funcall function)))
\f
;;;; routines to print objects

\f
;;; keyword variables shared by WRITE and WRITE-TO-STRING, and
;;; the bindings they map to.
(eval-when (:compile-toplevel :load-toplevel)
  (defvar *printer-keyword-variables*
    '(:escape *print-escape*
      :radix *print-radix*
      :base *print-base*
      :circle *print-circle*
      :pretty *print-pretty*
      :level *print-level*
      :length *print-length*
      :case *print-case*
      :array *print-array*
      :gensym *print-gensym*
      :readably *print-readably*
      :right-margin *print-right-margin*
      :miser-width *print-miser-width*
      :lines *print-lines*
      :pprint-dispatch *print-pprint-dispatch*)))

(defun write (object &key
                     ((:stream stream) *standard-output*)
                     ((:escape *print-escape*) *print-escape*)
                     ((:radix *print-radix*) *print-radix*)
                     ((:base *print-base*) *print-base*)
                     ((:circle *print-circle*) *print-circle*)
                     ((:pretty *print-pretty*) *print-pretty*)
                     ((:level *print-level*) *print-level*)
                     ((:length *print-length*) *print-length*)
                     ((:case *print-case*) *print-case*)
                     ((:array *print-array*) *print-array*)
                     ((:gensym *print-gensym*) *print-gensym*)
                     ((:readably *print-readably*) *print-readably*)
                     ((:right-margin *print-right-margin*)
                      *print-right-margin*)
                     ((:miser-width *print-miser-width*)
                      *print-miser-width*)
                     ((:lines *print-lines*) *print-lines*)
                     ((:pprint-dispatch *print-pprint-dispatch*)
                      *print-pprint-dispatch*))
  #!+sb-doc
  "Output OBJECT to the specified stream, defaulting to *STANDARD-OUTPUT*"
  (output-object object (out-synonym-of stream))
  object)

;;; Optimize common case of constant keyword arguments
(define-compiler-macro write (&whole form object &rest keys)
  (let (bind ignore)
    (do ()
        ((not (cdr keys))
         ;; Odd number of keys, punt
         (when keys
           (return-from write form)))
      (let* ((key (pop keys))
             (value (pop keys))
             (variable (or (getf *printer-keyword-variables* key)
                           (when (eq :stream key)
                             'stream)
                           (return-from write form))))
        (when (assoc variable bind)
          ;; First key has precedence, but we still need to execute the
          ;; argument, and in the right order.
          (setf variable (gensym "IGNORE"))
          (push variable ignore))
        (push (list variable value) bind)))
    (unless (assoc 'stream bind)
      (push (list 'stream '*standard-output*) bind))
    `(let ,(nreverse bind)
       ,@(when ignore `((declare (ignore ,@ignore))))
       (output-object ,object stream))))

(defun prin1 (object &optional stream)
  #!+sb-doc
  "Output a mostly READable printed representation of OBJECT on the specified
  STREAM."
  (let ((*print-escape* t))
    (output-object object (out-synonym-of stream)))
  object)

(defun princ (object &optional stream)
  #!+sb-doc
  "Output an aesthetic but not necessarily READable printed representation
  of OBJECT on the specified STREAM."
  (let ((*print-escape* nil)
        (*print-readably* nil))
    (output-object object (out-synonym-of stream)))
  object)

(defun print (object &optional stream)
  #!+sb-doc
  "Output a newline, the mostly READable printed representation of OBJECT, and
  space to the specified STREAM."
  (let ((stream (out-synonym-of stream)))
    (terpri stream)
    (prin1 object stream)
    (write-char #\space stream)
    object))

(defun pprint (object &optional stream)
  #!+sb-doc
  "Prettily output OBJECT preceded by a newline."
  (let ((*print-pretty* t)
        (*print-escape* t)
        (stream (out-synonym-of stream)))
    (terpri stream)
    (output-object object stream))
  (values))

(defun write-to-string
    (object &key
            ((:escape *print-escape*) *print-escape*)
            ((:radix *print-radix*) *print-radix*)
            ((:base *print-base*) *print-base*)
            ((:circle *print-circle*) *print-circle*)
            ((:pretty *print-pretty*) *print-pretty*)
            ((:level *print-level*) *print-level*)
            ((:length *print-length*) *print-length*)
            ((:case *print-case*) *print-case*)
            ((:array *print-array*) *print-array*)
            ((:gensym *print-gensym*) *print-gensym*)
            ((:readably *print-readably*) *print-readably*)
            ((:right-margin *print-right-margin*) *print-right-margin*)
            ((:miser-width *print-miser-width*) *print-miser-width*)
            ((:lines *print-lines*) *print-lines*)
            ((:pprint-dispatch *print-pprint-dispatch*)
             *print-pprint-dispatch*))
  #!+sb-doc
  "Return the printed representation of OBJECT as a string."
  (stringify-object object))

;;; Optimize common case of constant keyword arguments
(define-compiler-macro write-to-string (&whole form object &rest keys)
  (let (bind ignore)
    (do ()
        ((not (cdr keys))
         ;; Odd number of keys, punt
         (when keys
           (return-from write-to-string form)))
      (let* ((key (pop keys))
             (value (pop keys))
             (variable (or (getf *printer-keyword-variables* key)
                           (return-from write-to-string form))))
        (when (assoc variable bind)
          ;; First key has precedence, but we still need to execute the
          ;; argument, and in the right order.
          (setf variable (gensym "IGNORE"))
          (push variable ignore))
        (push (list variable value) bind)))
    (if bind
        `(let ,(nreverse bind)
           ,@(when ignore `((declare (ignore ,@ignore))))
           (stringify-object ,object))
        `(stringify-object ,object))))

(defun prin1-to-string (object)
  #!+sb-doc
  "Return the printed representation of OBJECT as a string with
   slashification on."
  (let ((*print-escape* t))
    (stringify-object object)))

(defun princ-to-string (object)
  #!+sb-doc
  "Return the printed representation of OBJECT as a string with
  slashification off."
  (let ((*print-escape* nil)
        (*print-readably* nil))
    (stringify-object object)))

;;; This produces the printed representation of an object as a string.
;;; The few ...-TO-STRING functions above call this.
(defun stringify-object (object)
  (let ((stream (make-string-output-stream)))
    (setup-printer-state)
    (output-object object stream)
    (get-output-stream-string stream)))
\f
;;;; support for the PRINT-UNREADABLE-OBJECT macro

;;; guts of PRINT-UNREADABLE-OBJECT
(defun %print-unreadable-object (object stream type identity body)
  (declare (type (or null function) body))
  (when *print-readably*
    (error 'print-not-readable :object object))
  (flet ((print-description ()
           (when type
             (write (type-of object) :stream stream :circle nil
                    :level nil :length nil)
             (write-char #\space stream))
           (when body
             (funcall body))
           (when identity
             (when (or body (not type))
               (write-char #\space stream))
             (write-char #\{ stream)
             (write (get-lisp-obj-address object) :stream stream
                    :radix nil :base 16)
             (write-char #\} stream))))
    (cond ((print-pretty-on-stream-p stream)
           ;; Since we're printing prettily on STREAM, format the
           ;; object within a logical block. PPRINT-LOGICAL-BLOCK does
           ;; not rebind the stream when it is already a pretty stream,
           ;; so output from the body will go to the same stream.
           (pprint-logical-block (stream nil :prefix "#<" :suffix ">")
             (print-description)))
          (t
            (write-string "#<" stream)
            (print-description)
            (write-char #\> stream))))
  nil)
\f
;;;; OUTPUT-OBJECT -- the main entry point

;;; Objects whose print representation identifies them EQLly don't
;;; need to be checked for circularity.
(defun uniquely-identified-by-print-p (x)
  (or (numberp x)
      (characterp x)
      (and (symbolp x)
           (symbol-package x))))

;;; Output OBJECT to STREAM observing all printer control variables.
(defun output-object (object stream)
  (labels ((print-it (stream)
             (if *print-pretty*
                 (sb!pretty:output-pretty-object object stream)
                 (output-ugly-object object stream)))
           (check-it (stream)
             (multiple-value-bind (marker initiate)
                 (check-for-circularity object t)
               (if (eq initiate :initiate)
                   (let ((*circularity-hash-table*
                          (make-hash-table :test 'eq)))
                     (check-it (make-broadcast-stream))
                     (let ((*circularity-counter* 0))
                       (check-it stream)))
                   ;; otherwise
                   (if marker
                       (when (handle-circularity marker stream)
                         (print-it stream))
                       (print-it stream))))))
    (cond (;; Maybe we don't need to bother with circularity detection.
           (or (not *print-circle*)
               (uniquely-identified-by-print-p object))
           (print-it stream))
          (;; If we have already started circularity detection, this
           ;; object might be a shared reference. If we have not, then
           ;; if it is a compound object it might contain a circular
           ;; reference to itself or multiple shared references.
           (or *circularity-hash-table*
               (compound-object-p object))
           (check-it stream))
          (t
           (print-it stream)))))

;;; a hack to work around recurring gotchas with printing while
;;; DEFGENERIC PRINT-OBJECT is being built
;;;
;;; (hopefully will go away naturally when CLOS moves into cold init)
(defvar *print-object-is-disabled-p*)

;;; Output OBJECT to STREAM observing all printer control variables
;;; except for *PRINT-PRETTY*. Note: if *PRINT-PRETTY* is non-NIL,
;;; then the pretty printer will be used for any components of OBJECT,
;;; just not for OBJECT itself.
(defun output-ugly-object (object stream)
  (typecase object
    ;; KLUDGE: The TYPECASE approach here is non-ANSI; the ANSI definition of
    ;; PRINT-OBJECT says it provides printing and we're supposed to provide
    ;; PRINT-OBJECT methods covering all classes. We deviate from this
    ;; by using PRINT-OBJECT only when we print instance values. However,
    ;; ANSI makes it hard to tell that we're deviating from this:
    ;;   (1) ANSI specifies that the user isn't supposed to call PRINT-OBJECT
    ;;       directly.
    ;;   (2) ANSI (section 11.1.2.1.2) says it's undefined to define
    ;;       a method on an external symbol in the CL package which is
    ;;       applicable to arg lists containing only direct instances of
    ;;       standardized classes.
    ;; Thus, in order for the user to detect our sleaziness in conforming
    ;; code, he has to do something relatively obscure like
    ;;   (1) actually use tools like FIND-METHOD to look for PRINT-OBJECT
    ;;       methods, or
    ;;   (2) define a PRINT-OBJECT method which is specialized on the stream
    ;;       value (e.g. a Gray stream object).
    ;; As long as no one comes up with a non-obscure way of detecting this
    ;; sleaziness, fixing this nonconformity will probably have a low
    ;; priority. -- WHN 2001-11-25
    (list
     (if (null object)
         (output-symbol object stream)
         (output-list object stream)))
    (instance
     (cond ((not (and (boundp '*print-object-is-disabled-p*)
                      *print-object-is-disabled-p*))
            (print-object object stream))
           ((typep object 'structure-object)
            (default-structure-print object stream *current-level-in-print*))
           (t
            (write-string "#<INSTANCE but not STRUCTURE-OBJECT>" stream))))
    (funcallable-instance
     (cond
       ((not (and (boundp '*print-object-is-disabled-p*)
                  *print-object-is-disabled-p*))
        (print-object object stream))
       (t (output-fun object stream))))
    (function
     (output-fun object stream))
    (symbol
     (output-symbol object stream))
    (number
     (etypecase object
       (integer
        (output-integer object stream))
       (float
        (output-float object stream))
       (ratio
        (output-ratio object stream))
       (ratio
        (output-ratio object stream))
       (complex
        (output-complex object stream))))
    (character
     (output-character object stream))
    (vector
     (output-vector object stream))
    (array
     (output-array object stream))
    (system-area-pointer
     (output-sap object stream))
    (weak-pointer
     (output-weak-pointer object stream))
    (lra
     (output-lra object stream))
    (code-component
     (output-code-component object stream))
    (fdefn
     (output-fdefn object stream))
    (t
     (output-random object stream))))
\f
;;;; symbols

;;; values of *PRINT-CASE* and (READTABLE-CASE *READTABLE*) the last
;;; time the printer was called
(defvar *previous-case* nil)
(defvar *previous-readtable-case* nil)

;;; This variable contains the current definition of one of three
;;; symbol printers. SETUP-PRINTER-STATE sets this variable.
(defvar *internal-symbol-output-fun* nil)

;;; This function sets the internal global symbol
;;; *INTERNAL-SYMBOL-OUTPUT-FUN* to the right function depending on
;;; the value of *PRINT-CASE*. See the manual for details. The print
;;; buffer stream is also reset.
(defun setup-printer-state ()
  (unless (and (eq *print-case* *previous-case*)
               (eq (readtable-case *readtable*) *previous-readtable-case*))
    (setq *previous-case* *print-case*)
    (setq *previous-readtable-case* (readtable-case *readtable*))
    (unless (member *print-case* '(:upcase :downcase :capitalize))
      (setq *print-case* :upcase)
      (error "invalid *PRINT-CASE* value: ~S" *previous-case*))
    (unless (member *previous-readtable-case*
                    '(:upcase :downcase :invert :preserve))
      (setf (readtable-case *readtable*) :upcase)
      (error "invalid READTABLE-CASE value: ~S" *previous-readtable-case*))

    (setq *internal-symbol-output-fun*
          (case *previous-readtable-case*
            (:upcase
             (case *print-case*
               (:upcase #'output-preserve-symbol)
               (:downcase #'output-lowercase-symbol)
               (:capitalize #'output-capitalize-symbol)))
            (:downcase
             (case *print-case*
               (:upcase #'output-uppercase-symbol)
               (:downcase #'output-preserve-symbol)
               (:capitalize #'output-capitalize-symbol)))
            (:preserve #'output-preserve-symbol)
            (:invert #'output-invert-symbol)))))

;;; Output PNAME (a symbol-name or package-name) surrounded with |'s,
;;; and with any embedded |'s or \'s escaped.
(defun output-quoted-symbol-name (pname stream)
  (write-char #\| stream)
  (dotimes (index (length pname))
    (let ((char (schar pname index)))
      (when (or (char= char #\\) (char= char #\|))
        (write-char #\\ stream))
      (write-char char stream)))
  (write-char #\| stream))

(defun output-symbol (object stream)
  (if (or *print-escape* *print-readably*)
      (let ((package (symbol-package object))
            (name (symbol-name object)))
        (cond
         ;; The ANSI spec "22.1.3.3.1 Package Prefixes for Symbols"
         ;; requires that keywords be printed with preceding colons
         ;; always, regardless of the value of *PACKAGE*.
         ((eq package *keyword-package*)
          (write-char #\: stream))
         ;; Otherwise, if the symbol's home package is the current
         ;; one, then a prefix is never necessary.
         ((eq package (sane-package)))
         ;; Uninterned symbols print with a leading #:.
         ((null package)
          (when (or *print-gensym* *print-readably*)
            (write-string "#:" stream)))
         (t
          (multiple-value-bind (symbol accessible)
              (find-symbol name (sane-package))
            ;; If we can find the symbol by looking it up, it need not
            ;; be qualified. This can happen if the symbol has been
            ;; inherited from a package other than its home package.
            (unless (and accessible (eq symbol object))
              (output-symbol-name (package-name package) stream)
              (multiple-value-bind (symbol externalp)
                  (find-external-symbol name package)
                (declare (ignore symbol))
                (if externalp
                    (write-char #\: stream)
                    (write-string "::" stream)))))))
        (output-symbol-name name stream))
      (output-symbol-name (symbol-name object) stream nil)))

;;; Output the string NAME as if it were a symbol name. In other
;;; words, diddle its case according to *PRINT-CASE* and
;;; READTABLE-CASE.
(defun output-symbol-name (name stream &optional (maybe-quote t))
  (declare (type simple-string name))
  (let ((*readtable* (if *print-readably* *standard-readtable* *readtable*)))
    (setup-printer-state)
    (if (and maybe-quote (symbol-quotep name))
        (output-quoted-symbol-name name stream)
        (funcall *internal-symbol-output-fun* name stream))))
\f
;;;; escaping symbols

;;; When we print symbols we have to figure out if they need to be
;;; printed with escape characters. This isn't a whole lot easier than
;;; reading symbols in the first place.
;;;
;;; For each character, the value of the corresponding element is a
;;; fixnum with bits set corresponding to attributes that the
;;; character has. At characters have at least one bit set, so we can
;;; search for any character with a positive test.
(defvar *character-attributes*
  (make-array 160 ; FIXME
              :element-type '(unsigned-byte 16)
              :initial-element 0))
(declaim (type (simple-array (unsigned-byte 16) (#.160)) ; FIXME
               *character-attributes*))

;;; constants which are a bit-mask for each interesting character attribute
(defconstant other-attribute            (ash 1 0)) ; Anything else legal.
(defconstant number-attribute           (ash 1 1)) ; A numeric digit.
(defconstant uppercase-attribute        (ash 1 2)) ; An uppercase letter.
(defconstant lowercase-attribute        (ash 1 3)) ; A lowercase letter.
(defconstant sign-attribute             (ash 1 4)) ; +-
(defconstant extension-attribute        (ash 1 5)) ; ^_
(defconstant dot-attribute              (ash 1 6)) ; .
(defconstant slash-attribute            (ash 1 7)) ; /
(defconstant funny-attribute            (ash 1 8)) ; Anything illegal.

(eval-when (:compile-toplevel :load-toplevel :execute)

;;; LETTER-ATTRIBUTE is a local of SYMBOL-QUOTEP. It matches letters
;;; that don't need to be escaped (according to READTABLE-CASE.)
(defparameter *attribute-names*
  `((number . number-attribute) (lowercase . lowercase-attribute)
    (uppercase . uppercase-attribute) (letter . letter-attribute)
    (sign . sign-attribute) (extension . extension-attribute)
    (dot . dot-attribute) (slash . slash-attribute)
    (other . other-attribute) (funny . funny-attribute)))

) ; EVAL-WHEN

(flet ((set-bit (char bit)
         (let ((code (char-code char)))
           (setf (aref *character-attributes* code)
                 (logior bit (aref *character-attributes* code))))))

  (dolist (char '(#\! #\@ #\$ #\% #\& #\* #\= #\~ #\[ #\] #\{ #\}
                  #\? #\< #\>))
    (set-bit char other-attribute))

  (dotimes (i 10)
    (set-bit (digit-char i) number-attribute))

  (do ((code (char-code #\A) (1+ code))
       (end (char-code #\Z)))
      ((> code end))
    (declare (fixnum code end))
    (set-bit (code-char code) uppercase-attribute)
    (set-bit (char-downcase (code-char code)) lowercase-attribute))

  (set-bit #\- sign-attribute)
  (set-bit #\+ sign-attribute)
  (set-bit #\^ extension-attribute)
  (set-bit #\_ extension-attribute)
  (set-bit #\. dot-attribute)
  (set-bit #\/ slash-attribute)

  ;; Mark anything not explicitly allowed as funny.
  (dotimes (i 160) ; FIXME
    (when (zerop (aref *character-attributes* i))
      (setf (aref *character-attributes* i) funny-attribute))))

;;; For each character, the value of the corresponding element is the
;;; lowest base in which that character is a digit.
(defvar *digit-bases*
  (make-array 128 ; FIXME
              :element-type '(unsigned-byte 8)
              :initial-element 36))
(declaim (type (simple-array (unsigned-byte 8) (#.128)) ; FIXME
               *digit-bases*))
(dotimes (i 36)
  (let ((char (digit-char i 36)))
    (setf (aref *digit-bases* (char-code char)) i)))

;;; A FSM-like thingie that determines whether a symbol is a potential
;;; number or has evil characters in it.
(defun symbol-quotep (name)
  (declare (simple-string name))
  (macrolet ((advance (tag &optional (at-end t))
               `(progn
                 (when (= index len)
                   ,(if at-end '(go TEST-SIGN) '(return nil)))
                 (setq current (schar name index)
                       code (char-code current)
                       bits (cond ; FIXME
                              ((< code 160) (aref attributes code))
                              ((upper-case-p current) uppercase-attribute)
                              ((lower-case-p current) lowercase-attribute)
                              (t other-attribute)))
                 (incf index)
                 (go ,tag)))
             (test (&rest attributes)
                `(not (zerop
                       (the fixnum
                            (logand
                             (logior ,@(mapcar
                                        (lambda (x)
                                          (or (cdr (assoc x
                                                          *attribute-names*))
                                              (error "Blast!")))
                                        attributes))
                             bits)))))
             (digitp ()
               `(and (< code 128) ; FIXME
                     (< (the fixnum (aref bases code)) base))))

    (prog ((len (length name))
           (attributes *character-attributes*)
           (bases *digit-bases*)
           (base *print-base*)
           (letter-attribute
            (case (readtable-case *readtable*)
              (:upcase uppercase-attribute)
              (:downcase lowercase-attribute)
              (t (logior lowercase-attribute uppercase-attribute))))
           (index 0)
           (bits 0)
           (code 0)
           current)
      (declare (fixnum len base index bits code))
      (advance START t)

     TEST-SIGN ; At end, see whether it is a sign...
      (return (not (test sign)))

     OTHER ; not potential number, see whether funny chars...
      (let ((mask (logxor (logior lowercase-attribute uppercase-attribute
                                  funny-attribute)
                          letter-attribute)))
        (do ((i (1- index) (1+ i)))
            ((= i len) (return-from symbol-quotep nil))
          (unless (zerop (logand (let* ((char (schar name i))
                                        (code (char-code char)))
                                   (cond
                                     ((< code 160) (aref attributes code))
                                     ((upper-case-p char) uppercase-attribute)
                                     ((lower-case-p char) lowercase-attribute)
                                     (t other-attribute)))
                                 mask))
            (return-from symbol-quotep t))))

     START
      (when (digitp)
        (if (test letter)
            (advance LAST-DIGIT-ALPHA)
            (advance DIGIT)))
      (when (test letter number other slash) (advance OTHER nil))
      (when (char= current #\.) (advance DOT-FOUND))
      (when (test sign extension) (advance START-STUFF nil))
      (return t)

     DOT-FOUND ; leading dots...
      (when (test letter) (advance START-DOT-MARKER nil))
      (when (digitp) (advance DOT-DIGIT))
      (when (test number other) (advance OTHER nil))
      (when (test extension slash sign) (advance START-DOT-STUFF nil))
      (when (char= current #\.) (advance DOT-FOUND))
      (return t)

     START-STUFF ; leading stuff before any dot or digit
      (when (digitp)
        (if (test letter)
            (advance LAST-DIGIT-ALPHA)
            (advance DIGIT)))
      (when (test number other) (advance OTHER nil))
      (when (test letter) (advance START-MARKER nil))
      (when (char= current #\.) (advance START-DOT-STUFF nil))
      (when (test sign extension slash) (advance START-STUFF nil))
      (return t)

     START-MARKER ; number marker in leading stuff...
      (when (test letter) (advance OTHER nil))
      (go START-STUFF)

     START-DOT-STUFF ; leading stuff containing dot without digit...
      (when (test letter) (advance START-DOT-STUFF nil))
      (when (digitp) (advance DOT-DIGIT))
      (when (test sign extension dot slash) (advance START-DOT-STUFF nil))
      (when (test number other) (advance OTHER nil))
      (return t)

     START-DOT-MARKER ; number marker in leading stuff with dot..
      ;; leading stuff containing dot without digit followed by letter...
      (when (test letter) (advance OTHER nil))
      (go START-DOT-STUFF)

     DOT-DIGIT ; in a thing with dots...
      (when (test letter) (advance DOT-MARKER))
      (when (digitp) (advance DOT-DIGIT))
      (when (test number other) (advance OTHER nil))
      (when (test sign extension dot slash) (advance DOT-DIGIT))
      (return t)

     DOT-MARKER ; number marker in number with dot...
      (when (test letter) (advance OTHER nil))
      (go DOT-DIGIT)

     LAST-DIGIT-ALPHA ; previous char is a letter digit...
      (when (or (digitp) (test sign slash))
        (advance ALPHA-DIGIT))
      (when (test letter number other dot) (advance OTHER nil))
      (return t)

     ALPHA-DIGIT ; seen a digit which is a letter...
      (when (or (digitp) (test sign slash))
        (if (test letter)
            (advance LAST-DIGIT-ALPHA)
            (advance ALPHA-DIGIT)))
      (when (test letter) (advance ALPHA-MARKER))
      (when (test number other dot) (advance OTHER nil))
      (return t)

     ALPHA-MARKER ; number marker in number with alpha digit...
      (when (test letter) (advance OTHER nil))
      (go ALPHA-DIGIT)

     DIGIT ; seen only ordinary (non-alphabetic) numeric digits...
      (when (digitp)
        (if (test letter)
            (advance ALPHA-DIGIT)
            (advance DIGIT)))
      (when (test number other) (advance OTHER nil))
      (when (test letter) (advance MARKER))
      (when (test extension slash sign) (advance DIGIT))
      (when (char= current #\.) (advance DOT-DIGIT))
      (return t)

     MARKER ; number marker in a numeric number...
      ;; ("What," you may ask, "is a 'number marker'?" It's something
      ;; that a conforming implementation might use in number syntax.
      ;; See ANSI 2.3.1.1 "Potential Numbers as Tokens".)
      (when (test letter) (advance OTHER nil))
      (go DIGIT))))
\f
;;;; *INTERNAL-SYMBOL-OUTPUT-FUN*
;;;;
;;;; case hackery: These functions are stored in
;;;; *INTERNAL-SYMBOL-OUTPUT-FUN* according to the values of
;;;; *PRINT-CASE* and READTABLE-CASE.

;;; called when:
;;; READTABLE-CASE      *PRINT-CASE*
;;; :UPCASE             :UPCASE
;;; :DOWNCASE           :DOWNCASE
;;; :PRESERVE           any
(defun output-preserve-symbol (pname stream)
  (declare (simple-string pname))
  (write-string pname stream))

;;; called when:
;;; READTABLE-CASE      *PRINT-CASE*
;;; :UPCASE             :DOWNCASE
(defun output-lowercase-symbol (pname stream)
  (declare (simple-string pname))
  (dotimes (index (length pname))
    (let ((char (schar pname index)))
      (write-char (char-downcase char) stream))))

;;; called when:
;;; READTABLE-CASE      *PRINT-CASE*
;;; :DOWNCASE           :UPCASE
(defun output-uppercase-symbol (pname stream)
  (declare (simple-string pname))
  (dotimes (index (length pname))
    (let ((char (schar pname index)))
      (write-char (char-upcase char) stream))))

;;; called when:
;;; READTABLE-CASE      *PRINT-CASE*
;;; :UPCASE             :CAPITALIZE
;;; :DOWNCASE           :CAPITALIZE
(defun output-capitalize-symbol (pname stream)
  (declare (simple-string pname))
  (let ((prev-not-alphanum t)
        (up (eq (readtable-case *readtable*) :upcase)))
    (dotimes (i (length pname))
      (let ((char (char pname i)))
        (write-char (if up
                        (if (or prev-not-alphanum (lower-case-p char))
                            char
                            (char-downcase char))
                        (if prev-not-alphanum
                            (char-upcase char)
                            char))
                    stream)
        (setq prev-not-alphanum (not (alphanumericp char)))))))

;;; called when:
;;; READTABLE-CASE      *PRINT-CASE*
;;; :INVERT             any
(defun output-invert-symbol (pname stream)
  (declare (simple-string pname))
  (let ((all-upper t)
        (all-lower t))
    (dotimes (i (length pname))
      (let ((ch (schar pname i)))
        (when (both-case-p ch)
          (if (upper-case-p ch)
              (setq all-lower nil)
              (setq all-upper nil)))))
    (cond (all-upper (output-lowercase-symbol pname stream))
          (all-lower (output-uppercase-symbol pname stream))
          (t
           (write-string pname stream)))))

#|
(defun test1 ()
  (let ((*readtable* (copy-readtable nil)))
    (format t "READTABLE-CASE  Input   Symbol-name~@
               ----------------------------------~%")
    (dolist (readtable-case '(:upcase :downcase :preserve :invert))
      (setf (readtable-case *readtable*) readtable-case)
      (dolist (input '("ZEBRA" "Zebra" "zebra"))
        (format t "~&:~A~16T~A~24T~A"
                (string-upcase readtable-case)
                input
                (symbol-name (read-from-string input)))))))

(defun test2 ()
  (let ((*readtable* (copy-readtable nil)))
    (format t "READTABLE-CASE  *PRINT-CASE*  Symbol-name  Output  Princ~@
               --------------------------------------------------------~%")
    (dolist (readtable-case '(:upcase :downcase :preserve :invert))
      (setf (readtable-case *readtable*) readtable-case)
      (dolist (*print-case* '(:upcase :downcase :capitalize))
        (dolist (symbol '(|ZEBRA| |Zebra| |zebra|))
          (format t "~&:~A~15T:~A~29T~A~42T~A~50T~A"
                  (string-upcase readtable-case)
                  (string-upcase *print-case*)
                  (symbol-name symbol)
                  (prin1-to-string symbol)
                  (princ-to-string symbol)))))))
|#
\f
;;;; recursive objects

(defun output-list (list stream)
  (descend-into (stream)
    (write-char #\( stream)
    (let ((length 0)
          (list list))
      (loop
        (punt-print-if-too-long length stream)
        (output-object (pop list) stream)
        (unless list
          (return))
        (when (or (atom list)
                  (check-for-circularity list))
          (write-string " . " stream)
          (output-object list stream)
          (return))
        (write-char #\space stream)
        (incf length)))
    (write-char #\) stream)))

(defun output-vector (vector stream)
  (declare (vector vector))
  (cond ((stringp vector)
         (cond ((and *print-readably*
                     (not (eq (array-element-type vector)
                              (load-time-value
                               (array-element-type
                                (make-array 0 :element-type 'character))))))
                (error 'print-not-readable :object vector))
               ((or *print-escape* *print-readably*)
                (write-char #\" stream)
                (quote-string vector stream)
                (write-char #\" stream))
               (t
                (write-string vector stream))))
        ((not (or *print-array* *print-readably*))
         (output-terse-array vector stream))
        ((bit-vector-p vector)
         (write-string "#*" stream)
         (dovector (bit vector)
           ;; (Don't use OUTPUT-OBJECT here, since this code
           ;; has to work for all possible *PRINT-BASE* values.)
           (write-char (if (zerop bit) #\0 #\1) stream)))
        (t
         (when (and *print-readably*
                    (not (array-readably-printable-p vector)))
           (error 'print-not-readable :object vector))
         (descend-into (stream)
                       (write-string "#(" stream)
                       (dotimes (i (length vector))
                         (unless (zerop i)
                           (write-char #\space stream))
                         (punt-print-if-too-long i stream)
                         (output-object (aref vector i) stream))
                       (write-string ")" stream)))))

;;; This function outputs a string quoting characters sufficiently
;;; so that someone can read it in again. Basically, put a slash in
;;; front of an character satisfying NEEDS-SLASH-P.
(defun quote-string (string stream)
  (macrolet ((needs-slash-p (char)
               ;; KLUDGE: We probably should look at the readtable, but just do
               ;; this for now. [noted by anonymous long ago] -- WHN 19991130
               `(or (char= ,char #\\)
                 (char= ,char #\"))))
    (with-array-data ((data string) (start) (end)
                      :check-fill-pointer t)
      (do ((index start (1+ index)))
          ((>= index end))
        (let ((char (schar data index)))
          (when (needs-slash-p char) (write-char #\\ stream))
          (write-char char stream))))))

(defun array-readably-printable-p (array)
  (and (eq (array-element-type array) t)
       (let ((zero (position 0 (array-dimensions array)))
             (number (position 0 (array-dimensions array)
                               :test (complement #'eql)
                               :from-end t)))
         (or (null zero) (null number) (> zero number)))))

;;; Output the printed representation of any array in either the #< or #A
;;; form.
(defun output-array (array stream)
  (if (or *print-array* *print-readably*)
      (output-array-guts array stream)
      (output-terse-array array stream)))

;;; Output the abbreviated #< form of an array.
(defun output-terse-array (array stream)
  (let ((*print-level* nil)
        (*print-length* nil))
    (print-unreadable-object (array stream :type t :identity t))))

;;; Output the readable #A form of an array.
(defun output-array-guts (array stream)
  (when (and *print-readably*
             (not (array-readably-printable-p array)))
    (error 'print-not-readable :object array))
  (write-char #\# stream)
  (let ((*print-base* 10)
        (*print-radix* nil))
    (output-integer (array-rank array) stream))
  (write-char #\A stream)
  (with-array-data ((data array) (start) (end))
    (declare (ignore end))
    (sub-output-array-guts data (array-dimensions array) stream start)))

(defun sub-output-array-guts (array dimensions stream index)
  (declare (type (simple-array * (*)) array) (fixnum index))
  (cond ((null dimensions)
         (output-object (aref array index) stream))
        (t
         (descend-into (stream)
           (write-char #\( stream)
           (let* ((dimension (car dimensions))
                  (dimensions (cdr dimensions))
                  (count (reduce #'* dimensions)))
             (dotimes (i dimension)
               (unless (zerop i)
                 (write-char #\space stream))
               (punt-print-if-too-long i stream)
               (sub-output-array-guts array dimensions stream index)
               (incf index count)))
           (write-char #\) stream)))))

;;; a trivial non-generic-function placeholder for PRINT-OBJECT, for
;;; use until CLOS is set up (at which time it will be replaced with
;;; the real generic function implementation)
(defun print-object (instance stream)
  (default-structure-print instance stream *current-level-in-print*))
\f
;;;; integer, ratio, and complex printing (i.e. everything but floats)

(defun %output-radix (base stream)
  (write-char #\# stream)
  (write-char (case base
                (2 #\b)
                (8 #\o)
                (16 #\x)
                (t (%output-reasonable-integer-in-base base 10 stream)
                   #\r))
              stream))

(defun %output-reasonable-integer-in-base (n base stream)
  (multiple-value-bind (q r)
      (truncate n base)
    ;; Recurse until you have all the digits pushed on
    ;; the stack.
    (unless (zerop q)
      (%output-reasonable-integer-in-base q base stream))
    ;; Then as each recursive call unwinds, turn the
    ;; digit (in remainder) into a character and output
    ;; the character.
    (write-char
     (schar "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" r)
     stream)))

;;; *POWER-CACHE* is an alist mapping bases to power-vectors. It is
;;; filled and probed by POWERS-FOR-BASE. SCRUB-POWER-CACHE is called
;;; always prior a GC to drop overly large bignums from the cache.
;;;
;;; It doesn't need a lock, but if you work on SCRUB-POWER-CACHE or
;;; POWERS-FOR-BASE, see that you don't break the assumptions!
(defvar *power-cache* nil)

(defconstant +power-cache-integer-length-limit+ 2048)

(defun scrub-power-cache ()
  (let ((cache *power-cache*))
    (dolist (cell cache)
      (let ((powers (cdr cell)))
        (declare (simple-vector powers))
        (let ((too-big (position-if
                        (lambda (x)
                          (>= (integer-length x)
                              +power-cache-integer-length-limit+))
                        powers)))
          (when too-big
            (setf (cdr cell) (subseq powers 0 too-big))))))
    ;; Since base 10 is overwhelmingly common, make sure it's at head.
    ;; Try to keep other bases in a hopefully sensible order as well.
    (if (eql 10 (caar cache))
        (setf *power-cache* cache)
        ;; If we modify the list destructively we need to copy it, otherwise
        ;; an alist lookup in progress might be screwed.
        (setf *power-cache* (sort (copy-list cache)
                                  (lambda (a b)
                                    (declare (fixnum a b))
                                    (cond ((= 10 a) t)
                                          ((= 10 b) nil)
                                          ((= 16 a) t)
                                          ((= 16 b) nil)
                                          ((= 2 a) t)
                                          ((= 2 b) nil)
                                          (t (< a b))))
                                  :key #'car)))))

;;; Compute (and cache) a power vector for a BASE and LIMIT:
;;; the vector holds integers for which
;;;    (aref powers k) == (expt base (expt 2 k))
;;; holds.
(defun powers-for-base (base limit)
  (flet ((compute-powers (from)
           (let (powers)
             (do ((p from (* p p)))
                 ((> p limit)
                  ;; We don't actually need this, but we also
                  ;; prefer not to cons it up a second time...
                  (push p powers))
               (push p powers))
             (nreverse powers))))
    ;; Grab a local reference so that we won't stuff consed at the
    ;; head by other threads -- or sorting by SCRUB-POWER-CACHE.
    (let ((cache *power-cache*))
      (let ((cell (assoc base cache)))
        (if cell
            (let* ((powers (cdr cell))
                   (len (length powers))
                   (max (svref powers (1- len))))
              (if (> max limit)
                  powers
                  (let ((new
                         (concatenate 'vector powers
                                      (compute-powers (* max max)))))
                    (setf (cdr cell) new)
                    new)))
            (let ((powers (coerce (compute-powers base) 'vector)))
              ;; Add new base to head: SCRUB-POWER-CACHE will later
              ;; put it to a better place.
              (setf *power-cache* (acons base powers cache))
              powers))))))

;; Algorithm by Harald Hanche-Olsen, sbcl-devel 2005-02-05
(defun %output-huge-integer-in-base (n base stream)
  (declare (type bignum n) (type fixnum base))
  ;; POWER is a vector for which the following holds:
  ;;   (aref power k) == (expt base (expt 2 k))
  (let* ((power (powers-for-base base n))
         (k-start (or (position-if (lambda (x) (> x n)) power)
                      (bug "power-vector too short"))))
    (labels ((bisect (n k exactp)
               (declare (fixnum k))
               ;; N is the number to bisect
               ;; K on initial entry BASE^(2^K) > N
               ;; EXACTP is true if 2^K is the exact number of digits
               (cond ((zerop n)
                      (when exactp
                        (loop repeat (ash 1 k) do (write-char #\0 stream))))
                     ((zerop k)
                      (write-char
                       (schar "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" n)
                       stream))
                     (t
                      (setf k (1- k))
                      (multiple-value-bind (q r) (truncate n (aref power k))
                        ;; EXACTP is NIL only at the head of the
                        ;; initial number, as we don't know the number
                        ;; of digits there, but we do know that it
                        ;; doesn't get any leading zeros.
                        (bisect q k exactp)
                        (bisect r k (or exactp (plusp q))))))))
      (bisect n k-start nil))))

(defun %output-integer-in-base (integer base stream)
  (when (minusp integer)
    (write-char #\- stream)
    (setf integer (- integer)))
  ;; The ideal cutoff point between these two algorithms is almost
  ;; certainly quite platform dependent: this gives 87 for 32 bit
  ;; SBCL, which is about right at least for x86/Darwin.
  (if (or (fixnump integer)
          (< (integer-length integer) (* 3 sb!vm:n-positive-fixnum-bits)))
      (%output-reasonable-integer-in-base integer base stream)
      (%output-huge-integer-in-base integer base stream)))

(defun output-integer (integer stream)
  (let ((base *print-base*))
    (when (and (/= base 10) *print-radix*)
      (%output-radix base stream))
    (%output-integer-in-base integer base stream)
    (when (and *print-radix* (= base 10))
      (write-char #\. stream))))

(defun output-ratio (ratio stream)
  (let ((base *print-base*))
    (when *print-radix*
      (%output-radix base stream))
    (%output-integer-in-base (numerator ratio) base stream)
    (write-char #\/ stream)
    (%output-integer-in-base (denominator ratio) base stream)))

(defun output-complex (complex stream)
  (write-string "#C(" stream)
  ;; FIXME: Could this just be OUTPUT-NUMBER?
  (output-object (realpart complex) stream)
  (write-char #\space stream)
  (output-object (imagpart complex) stream)
  (write-char #\) stream))
\f
;;;; float printing

;;; FLONUM-TO-STRING (and its subsidiary function FLOAT-STRING) does
;;; most of the work for all printing of floating point numbers in
;;; FORMAT.  It converts a floating point number to a string in a free
;;; or fixed format with no exponent. The interpretation of the
;;; arguments is as follows:
;;;
;;;     X       - The floating point number to convert, which must not be
;;;             negative.
;;;     WIDTH    - The preferred field width, used to determine the number
;;;             of fraction digits to produce if the FDIGITS parameter
;;;             is unspecified or NIL. If the non-fraction digits and the
;;;             decimal point alone exceed this width, no fraction digits
;;;             will be produced unless a non-NIL value of FDIGITS has been
;;;             specified. Field overflow is not considerd an error at this
;;;             level.
;;;     FDIGITS  - The number of fractional digits to produce. Insignificant
;;;             trailing zeroes may be introduced as needed. May be
;;;             unspecified or NIL, in which case as many digits as possible
;;;             are generated, subject to the constraint that there are no
;;;             trailing zeroes.
;;;     SCALE    - If this parameter is specified or non-NIL, then the number
;;;             printed is (* x (expt 10 scale)). This scaling is exact,
;;;             and cannot lose precision.
;;;     FMIN     - This parameter, if specified or non-NIL, is the minimum
;;;             number of fraction digits which will be produced, regardless
;;;             of the value of WIDTH or FDIGITS. This feature is used by
;;;             the ~E format directive to prevent complete loss of
;;;             significance in the printed value due to a bogus choice of
;;;             scale factor.
;;;
;;; Returns:
;;; (VALUES DIGIT-STRING DIGIT-LENGTH LEADING-POINT TRAILING-POINT DECPNT)
;;; where the results have the following interpretation:
;;;
;;;     DIGIT-STRING    - The decimal representation of X, with decimal point.
;;;     DIGIT-LENGTH    - The length of the string DIGIT-STRING.
;;;     LEADING-POINT   - True if the first character of DIGIT-STRING is the
;;;                    decimal point.
;;;     TRAILING-POINT  - True if the last character of DIGIT-STRING is the
;;;                    decimal point.
;;;     POINT-POS       - The position of the digit preceding the decimal
;;;                    point. Zero indicates point before first digit.
;;;
;;; NOTE: FLONUM-TO-STRING goes to a lot of trouble to guarantee
;;; accuracy. Specifically, the decimal number printed is the closest
;;; possible approximation to the true value of the binary number to
;;; be printed from among all decimal representations with the same
;;; number of digits. In free-format output, i.e. with the number of
;;; digits unconstrained, it is guaranteed that all the information is
;;; preserved, so that a properly- rounding reader can reconstruct the
;;; original binary number, bit-for-bit, from its printed decimal
;;; representation. Furthermore, only as many digits as necessary to
;;; satisfy this condition will be printed.
;;;
;;; FLOAT-DIGITS actually generates the digits for positive numbers;
;;; see below for comments.

(defun flonum-to-string (x &optional width fdigits scale fmin)
  (declare (type float x))
  ;; FIXME: I think only FORMAT-DOLLARS calls FLONUM-TO-STRING with
  ;; possibly-negative X.
  (setf x (abs x))
  (cond ((zerop x)
         ;; Zero is a special case which FLOAT-STRING cannot handle.
         (if fdigits
             (let ((s (make-string (1+ fdigits) :initial-element #\0)))
               (setf (schar s 0) #\.)
               (values s (length s) t (zerop fdigits) 0))
             (values "." 1 t t 0)))
        (t
         (multiple-value-bind (e string)
             (if fdigits
                 (flonum-to-digits x (min (- (+ fdigits (or scale 0)))
                                          (- (or fmin 0))))
                 (if (and width (> width 1))
                     (let ((w (multiple-value-list
                               (flonum-to-digits x
                                                 (max 1
                                                      (+ (1- width)
                                                         (if (and scale (minusp scale))
                                                             scale 0)))
                                                 t)))
                           (f (multiple-value-list
                               (flonum-to-digits x (- (+ (or fmin 0)
                                                         (if scale scale 0)))))))
                       (cond
                         ((>= (length (cadr w)) (length (cadr f)))
                          (values-list w))
                         (t (values-list f))))
                     (flonum-to-digits x)))
           (let ((e (+ e (or scale 0)))
                 (stream (make-string-output-stream)))
             (if (plusp e)
                 (progn
                   (write-string string stream :end (min (length string)
                                                         e))
                   (dotimes (i (- e (length string)))
                     (write-char #\0 stream))
                   (write-char #\. stream)
                   (write-string string stream :start (min (length
                                                            string) e))
                   (when fdigits
                     (dotimes (i (- fdigits
                                    (- (length string)
                                       (min (length string) e))))
                       (write-char #\0 stream))))
                 (progn
                   (write-string "." stream)
                   (dotimes (i (- e))
                     (write-char #\0 stream))
                   (write-string string stream)
                   (when fdigits
                     (dotimes (i (+ fdigits e (- (length string))))
                       (write-char #\0 stream)))))
             (let ((string (get-output-stream-string stream)))
               (values string (length string)
                       (char= (char string 0) #\.)
                       (char= (char string (1- (length string))) #\.)
                       (position #\. string))))))))

;;; implementation of figure 1 from Burger and Dybvig, 1996.  As the
;;; implementation of the Dragon from Classic CMUCL (and previously in
;;; SBCL above FLONUM-TO-STRING) says: "DO NOT EVEN THINK OF
;;; ATTEMPTING TO UNDERSTAND THIS CODE WITHOUT READING THE PAPER!",
;;; and in this case we have to add that even reading the paper might
;;; not bring immediate illumination as CSR has attempted to turn
;;; idiomatic Scheme into idiomatic Lisp.
;;;
;;; FIXME: figure 1 from Burger and Dybvig is the unoptimized
;;; algorithm, noticeably slow at finding the exponent.  Figure 2 has
;;; an improved algorithm, but CSR ran out of energy.
;;;
;;; possible extension for the enthusiastic: printing floats in bases
;;; other than base 10.
(defconstant single-float-min-e
  (nth-value 1 (decode-float least-positive-single-float)))
(defconstant double-float-min-e
  (nth-value 1 (decode-float least-positive-double-float)))
#!+long-float
(defconstant long-float-min-e
  (nth-value 1 (decode-float least-positive-long-float)))

(defun flonum-to-digits (v &optional position relativep)
  (let ((print-base 10) ; B
        (float-radix 2) ; b
        (float-digits (float-digits v)) ; p
        (digit-characters "0123456789")
        (min-e
         (etypecase v
           (single-float single-float-min-e)
           (double-float double-float-min-e)
           #!+long-float
           (long-float long-float-min-e))))
    (multiple-value-bind (f e)
        (integer-decode-float v)
      (let (;; FIXME: these even tests assume normal IEEE rounding
            ;; mode.  I wonder if we should cater for non-normal?
            (high-ok (evenp f))
            (low-ok (evenp f)))
        (with-push-char (:element-type base-char)
          (labels ((scale (r s m+ m-)
                     (do ((k 0 (1+ k))
                          (s s (* s print-base)))
                         ((not (or (> (+ r m+) s)
                                   (and high-ok (= (+ r m+) s))))
                          (do ((k k (1- k))
                               (r r (* r print-base))
                               (m+ m+ (* m+ print-base))
                               (m- m- (* m- print-base)))
                              ((not (or (< (* (+ r m+) print-base) s)
                                        (and (not high-ok)
                                             (= (* (+ r m+) print-base) s))))
                               (values k (generate r s m+ m-)))))))
                   (generate (r s m+ m-)
                     (let (d tc1 tc2)
                       (tagbody
                        loop
                          (setf (values d r) (truncate (* r print-base) s))
                          (setf m+ (* m+ print-base))
                          (setf m- (* m- print-base))
                          (setf tc1 (or (< r m-) (and low-ok (= r m-))))
                          (setf tc2 (or (> (+ r m+) s)
                                        (and high-ok (= (+ r m+) s))))
                          (when (or tc1 tc2)
                            (go end))
                          (push-char (char digit-characters d))
                          (go loop)
                        end
                          (let ((d (cond
                                     ((and (not tc1) tc2) (1+ d))
                                     ((and tc1 (not tc2)) d)
                                     (t ; (and tc1 tc2)
                                      (if (< (* r 2) s) d (1+ d))))))
                            (push-char (char digit-characters d))
                            (return-from generate (get-pushed-string))))))
                   (initialize ()
                     (let (r s m+ m-)
                       (if (>= e 0)
                           (let* ((be (expt float-radix e))
                                  (be1 (* be float-radix)))
                             (if (/= f (expt float-radix (1- float-digits)))
                                 (setf r (* f be 2)
                                       s 2
                                       m+ be
                                       m- be)
                                 (setf r (* f be1 2)
                                       s (* float-radix 2)
                                       m+ be1
                                       m- be)))
                           (if (or (= e min-e)
                                   (/= f (expt float-radix (1- float-digits))))
                               (setf r (* f 2)
                                     s (* (expt float-radix (- e)) 2)
                                     m+ 1
                                     m- 1)
                               (setf r (* f float-radix 2)
                                     s (* (expt float-radix (- 1 e)) 2)
                                     m+ float-radix
                                     m- 1)))
                       (when position
                         (when relativep
                           (aver (> position 0))
                           (do ((k 0 (1+ k))
                                ;; running out of letters here
                                (l 1 (* l print-base)))
                               ((>= (* s l) (+ r m+))
                                ;; k is now \hat{k}
                                (if (< (+ r (* s (/ (expt print-base (- k position)) 2)))
                                       (* s (expt print-base k)))
                                    (setf position (- k position))
                                    (setf position (- k position 1))))))
                         (let ((low (max m- (/ (* s (expt print-base position)) 2)))
                               (high (max m+ (/ (* s (expt print-base position)) 2))))
                           (when (<= m- low)
                             (setf m- low)
                             (setf low-ok t))
                           (when (<= m+ high)
                             (setf m+ high)
                             (setf high-ok t))))
                       (values r s m+ m-))))
            (multiple-value-bind (r s m+ m-) (initialize)
              (scale r s m+ m-))))))))
\f
;;; Given a non-negative floating point number, SCALE-EXPONENT returns
;;; a new floating point number Z in the range (0.1, 1.0] and an
;;; exponent E such that Z * 10^E is (approximately) equal to the
;;; original number. There may be some loss of precision due the
;;; floating point representation. The scaling is always done with
;;; long float arithmetic, which helps printing of lesser precisions
;;; as well as avoiding generic arithmetic.
;;;
;;; When computing our initial scale factor using EXPT, we pull out
;;; part of the computation to avoid over/under flow. When
;;; denormalized, we must pull out a large factor, since there is more
;;; negative exponent range than positive range.

(eval-when (:compile-toplevel :execute)
  (setf *read-default-float-format*
        #!+long-float 'long-float #!-long-float 'double-float))
(defun scale-exponent (original-x)
  (let* ((x (coerce original-x 'long-float)))
    (multiple-value-bind (sig exponent) (decode-float x)
      (declare (ignore sig))
      (if (= x 0.0e0)
          (values (float 0.0e0 original-x) 1)
          (let* ((ex (locally (declare (optimize (safety 0)))
                       (the fixnum
                         (round (* exponent (log 2e0 10))))))
                 (x (if (minusp ex)
                        (if (float-denormalized-p x)
                            #!-long-float
                            (* x 1.0e16 (expt 10.0e0 (- (- ex) 16)))
                            #!+long-float
                            (* x 1.0e18 (expt 10.0e0 (- (- ex) 18)))
                            (* x 10.0e0 (expt 10.0e0 (- (- ex) 1))))
                        (/ x 10.0e0 (expt 10.0e0 (1- ex))))))
            (do ((d 10.0e0 (* d 10.0e0))
                 (y x (/ x d))
                 (ex ex (1+ ex)))
                ((< y 1.0e0)
                 (do ((m 10.0e0 (* m 10.0e0))
                      (z y (* y m))
                      (ex ex (1- ex)))
                     ((>= z 0.1e0)
                      (values (float z original-x) ex))
                   (declare (long-float m) (integer ex))))
              (declare (long-float d))))))))
(eval-when (:compile-toplevel :execute)
  (setf *read-default-float-format* 'single-float))
\f
;;;; entry point for the float printer

;;; the float printer as called by PRINT, PRIN1, PRINC, etc. The
;;; argument is printed free-format, in either exponential or
;;; non-exponential notation, depending on its magnitude.
;;;
;;; NOTE: When a number is to be printed in exponential format, it is
;;; scaled in floating point. Since precision may be lost in this
;;; process, the guaranteed accuracy properties of FLONUM-TO-STRING
;;; are lost. The difficulty is that FLONUM-TO-STRING performs
;;; extensive computations with integers of similar magnitude to that
;;; of the number being printed. For large exponents, the bignums
;;; really get out of hand. If bignum arithmetic becomes reasonably
;;; fast and the exponent range is not too large, then it might become
;;; attractive to handle exponential notation with the same accuracy
;;; as non-exponential notation, using the method described in the
;;; Steele and White paper.
;;;
;;; NOTE II: this has been bypassed slightly by implementing Burger
;;; and Dybvig, 1996.  When someone has time (KLUDGE) they can
;;; probably (a) implement the optimizations suggested by Burger and
;;; Dyvbig, and (b) remove all vestiges of Dragon4, including from
;;; fixed-format printing.

;;; Print the appropriate exponent marker for X and the specified exponent.
(defun print-float-exponent (x exp stream)
  (declare (type float x) (type integer exp) (type stream stream))
  (let ((*print-radix* nil))
    (if (typep x *read-default-float-format*)
        (unless (eql exp 0)
          (format stream "e~D" exp))
        (format stream "~C~D"
                (etypecase x
                  (single-float #\f)
                  (double-float #\d)
                  (short-float #\s)
                  (long-float #\L))
                exp))))

(defun output-float-infinity (x stream)
  (declare (float x) (stream stream))
  (cond (*read-eval*
         (write-string "#." stream))
        (*print-readably*
         (error 'print-not-readable :object x))
        (t
         (write-string "#<" stream)))
  (write-string "SB-EXT:" stream)
  (write-string (symbol-name (float-format-name x)) stream)
  (write-string (if (plusp x) "-POSITIVE-" "-NEGATIVE-")
                stream)
  (write-string "INFINITY" stream)
  (unless *read-eval*
    (write-string ">" stream)))

(defun output-float-nan (x stream)
  (print-unreadable-object (x stream)
    (princ (float-format-name x) stream)
    (write-string (if (float-trapping-nan-p x) " trapping" " quiet") stream)
    (write-string " NaN" stream)))

;;; the function called by OUTPUT-OBJECT to handle floats
(defun output-float (x stream)
  (cond
   ((float-infinity-p x)
    (output-float-infinity x stream))
   ((float-nan-p x)
    (output-float-nan x stream))
   (t
    (let ((x (cond ((minusp (float-sign x))
                    (write-char #\- stream)
                    (- x))
                   (t
                    x))))
      (cond
       ((zerop x)
        (write-string "0.0" stream)
        (print-float-exponent x 0 stream))
       (t
        (output-float-aux x stream -3 8)))))))

(defun output-float-aux (x stream e-min e-max)
  (multiple-value-bind (e string)
      (flonum-to-digits x)
    (cond
      ((< e-min e e-max)
       (if (plusp e)
           (progn
             (write-string string stream :end (min (length string) e))
             (dotimes (i (- e (length string)))
               (write-char #\0 stream))
             (write-char #\. stream)
             (write-string string stream :start (min (length string) e))
             (when (<= (length string) e)
               (write-char #\0 stream))
             (print-float-exponent x 0 stream))
           (progn
             (write-string "0." stream)
             (dotimes (i (- e))
               (write-char #\0 stream))
             (write-string string stream)
             (print-float-exponent x 0 stream))))
      (t (write-string string stream :end 1)
         (write-char #\. stream)
         (write-string string stream :start 1)
         (print-float-exponent x (1- e) stream)))))
\f
;;;; other leaf objects

;;; If *PRINT-ESCAPE* is false, just do a WRITE-CHAR, otherwise output
;;; the character name or the character in the #\char format.
(defun output-character (char stream)
  (if (or *print-escape* *print-readably*)
      (let ((graphicp (and (graphic-char-p char)
                           (standard-char-p char)))
            (name (char-name char)))
        (write-string "#\\" stream)
        (if (and name (not graphicp))
            (quote-string name stream)
            (write-char char stream)))
      (write-char char stream)))

(defun output-sap (sap stream)
  (declare (type system-area-pointer sap))
  (cond (*read-eval*
         (format stream "#.(~S #X~8,'0X)" 'int-sap (sap-int sap)))
        (t
         (print-unreadable-object (sap stream)
           (format stream "system area pointer: #X~8,'0X" (sap-int sap))))))

(defun output-weak-pointer (weak-pointer stream)
  (declare (type weak-pointer weak-pointer))
  (print-unreadable-object (weak-pointer stream)
    (multiple-value-bind (value validp) (weak-pointer-value weak-pointer)
      (cond (validp
             (write-string "weak pointer: " stream)
             (write value :stream stream))
            (t
             (write-string "broken weak pointer" stream))))))

(defun output-code-component (component stream)
  (print-unreadable-object (component stream :identity t)
    (let ((dinfo (%code-debug-info component)))
      (cond ((eq dinfo :bogus-lra)
             (write-string "bogus code object" stream))
            (t
             (write-string "code object" stream)
             (when dinfo
               (write-char #\space stream)
               (output-object (sb!c::debug-info-name dinfo) stream)))))))

(defun output-lra (lra stream)
  (print-unreadable-object (lra stream :identity t)
    (write-string "return PC object" stream)))

(defun output-fdefn (fdefn stream)
  (print-unreadable-object (fdefn stream)
    (write-string "FDEFINITION object for " stream)
    (output-object (fdefn-name fdefn) stream)))
\f
;;;; functions

;;; Output OBJECT as using PRINT-OBJECT if it's a
;;; FUNCALLABLE-STANDARD-CLASS, or return NIL otherwise.
;;;
;;; The definition here is a simple temporary placeholder. It will be
;;; overwritten by a smarter version (capable of calling generic
;;; PRINT-OBJECT when appropriate) when CLOS is installed.
(defun printed-as-funcallable-standard-class (object stream)
  (declare (ignore object stream))
  nil)

(defun output-fun (object stream)
    (let* ((*print-length* 3)  ; in case we have to..
           (*print-level* 3)  ; ..print an interpreted function definition
           (name (%fun-name object))
           (proper-name-p (and (legal-fun-name-p name) (fboundp name)
                               (eq (fdefinition name) object))))
      (print-unreadable-object (object stream :identity (not proper-name-p))
        (format stream "~:[FUNCTION~;CLOSURE~]~@[ ~S~]"
                (closurep object)
                name))))
\f
;;;; catch-all for unknown things

(defun output-random (object stream)
  (print-unreadable-object (object stream :identity t)
    (let ((lowtag (lowtag-of object)))
      (case lowtag
        (#.sb!vm:other-pointer-lowtag
          (let ((widetag (widetag-of object)))
            (case widetag
              (#.sb!vm:value-cell-header-widetag
               (write-string "value cell " stream)
               (output-object (value-cell-ref object) stream))
              (t
               (write-string "unknown pointer object, widetag=" stream)
               (let ((*print-base* 16) (*print-radix* t))
                 (output-integer widetag stream))))))
        ((#.sb!vm:fun-pointer-lowtag
          #.sb!vm:instance-pointer-lowtag
          #.sb!vm:list-pointer-lowtag)
         (write-string "unknown pointer object, lowtag=" stream)
         (let ((*print-base* 16) (*print-radix* t))
           (output-integer lowtag stream)))
        (t
         (case (widetag-of object)
           (#.sb!vm:unbound-marker-widetag
            (write-string "unbound marker" stream))
           (t
            (write-string "unknown immediate object, lowtag=" stream)
            (let ((*print-base* 2) (*print-radix* t))
              (output-integer lowtag stream))
            (write-string ", widetag=" stream)
            (let ((*print-base* 16) (*print-radix* t))
              (output-integer (widetag-of object) stream)))))))))