guile/ice-9/format.scm

;;;; "format.scm" Common LISP text output formatter for SLIB
;;; Written 1992-1994 by Dirk Lutzebaeck (lutzeb@cs.tu-berlin.de)
;;; Assimilated into Guile May 1999
;;
;; This code is in the public domain.

;; Authors of the original version (< 1.4) were Ken Dickey and Aubrey Jaffer.
;; Please send error reports to bug-guile@gnu.org.
;; For documentation see slib.texi and format.doc.
;; For testing load formatst.scm.
;;
;; Version 3.0

(define-module (ice-9 format)
  :use-module (ice-9 and-let-star)
  :autoload (ice-9 pretty-print) (pretty-print)
  :replace (format)
  :export (format:symbol-case-conv
	   format:iobj-case-conv
	   format:expch))

;;; Configuration ------------------------------------------------------------

(define format:symbol-case-conv #f)
;; Symbols are converted by symbol->string so the case of the printed
;; symbols is implementation dependent. format:symbol-case-conv is a
;; one arg closure which is either #f (no conversion), string-upcase!,
;; string-downcase! or string-capitalize!.

(define format:iobj-case-conv #f)
;; As format:symbol-case-conv but applies for the representation of
;; implementation internal objects.

(define format:expch #\E)
;; The character prefixing the exponent value in ~e printing.

(define format:floats (provided? 'inexact))
;; Detects if the scheme system implements flonums (see at eof).

(define format:complex-numbers (provided? 'complex))
;; Detects if the scheme system implements complex numbers.

(define format:radix-pref (char=? #\# (string-ref (number->string 8 8) 0)))
;; Detects if number->string adds a radix prefix.

(define format:ascii-non-printable-charnames
  '#("nul" "soh" "stx" "etx" "eot" "enq" "ack" "bel"
     "bs"  "ht"  "nl"  "vt"  "np"  "cr"  "so"  "si"
     "dle" "dc1" "dc2" "dc3" "dc4" "nak" "syn" "etb"
     "can" "em"  "sub" "esc" "fs"  "gs"  "rs"  "us" "space"))

;;; End of configuration ----------------------------------------------------

(define (format . args)
  (letrec
      ((format:version "3.0")
       (format:port #f)			; curr. format output port
       (format:output-col 0)		; curr. format output tty column
       (format:flush-output #f)		; flush output at end of formatting
       (format:case-conversion #f)
       (format:args #f)
       (format:pos 0)			; curr. format string parsing position
       (format:arg-pos 0)		; curr. format argument position
					; this is global for error presentation
       
       ;; format string and char output routines on format:port

       (format:out-str
	(lambda (str)
	  (if format:case-conversion
	      (display (format:case-conversion str) format:port)
	      (display str format:port))
	  (set! format:output-col
		(+ format:output-col (string-length str)))))

       (format:out-char
	(lambda (ch)
	  (if format:case-conversion
	      (display (format:case-conversion (string ch))
		       format:port)
	      (write-char ch format:port))
	  (set! format:output-col
		(if (char=? ch #\newline)
		    0
		    (+ format:output-col 1)))))
       
       ;;(define (format:out-substr str i n)  ; this allocates a new string
       ;;  (display (substring str i n) format:port)
       ;;  (set! format:output-col (+ format:output-col n)))

       (format:out-substr
	(lambda (str i n)
	  (do ((k i (+ k 1)))
	      ((= k n))
	    (write-char (string-ref str k) format:port))
	  (set! format:output-col (+ format:output-col (- n i)))))

       ;;(define (format:out-fill n ch)       ; this allocates a new string
       ;;  (format:out-str (make-string n ch)))

       (format:out-fill
	(lambda (n ch)
	  (do ((i 0 (+ i 1)))
	      ((= i n))
	    (write-char ch format:port))
	  (set! format:output-col (+ format:output-col n))))

       ;; format's user error handler

       (format:error
	(lambda args		; never returns!
	  (let ((format-args format:args)
		(port (current-error-port)))
	    (set! format:error format:intern-error)
	    (if (and (>= (length format:args) 2)
		     (string? (cadr format:args)))
		(let ((format-string (cadr format-args)))
		  (if (not (zero? format:arg-pos))
		      (set! format:arg-pos (- format:arg-pos 1)))
		  (format port
			  "~%FORMAT: error with call: (format ~a \"~a<===~a\" ~
                                  ~{~a ~}===>~{~a ~})~%        "
			  (car format:args)
			  (substring format-string 0 format:pos)
			  (substring format-string format:pos
				     (string-length format-string))
			  (list-head (cddr format:args) format:arg-pos)
			  (list-tail (cddr format:args) format:arg-pos)))
		(format port 
			"~%FORMAT: error with call: (format~{ ~a~})~%        "
			format:args))
	    (apply format port args)
	    (newline port)
	    (set! format:error format:error-save)
	    (format:abort))))

       (format:intern-error
	(lambda args
	  ;;if something goes wrong in format:error
	  (display "FORMAT: INTERNAL ERROR IN FORMAT:ERROR!") (newline)
	  (display "        format args: ") (write format:args) (newline)
	  (display "        error args:  ") (write args) (newline)
	  (set! format:error format:error-save)
	  (format:abort)))
	      
       (format:error-save #f)

       (format:format
	(lambda args		; the formatter entry
	  (set! format:args args)
	  (set! format:arg-pos 0)
	  (set! format:pos 0)
	  (if (< (length args) 1)
	      (format:error "not enough arguments"))

	  ;; If the first argument is a string, then that's the format string.
	  ;; (Scheme->C)
	  ;; In this case, put the argument list in canonical form.
	  (let ((args (if (string? (car args))
			  (cons #f args)
			  args)))
	    ;; Use this canonicalized version when reporting errors.
	    (set! format:args args)

	    (let ((destination (car args))
		  (arglist (cdr args)))
	      (cond
	       ((or (and (boolean? destination)	; port output
			 destination)
		    (output-port? destination)
		    (number? destination))
		(format:out (cond
			     ((boolean? destination) (current-output-port))
			     ((output-port? destination) destination)
			     ((number? destination) (current-error-port)))
			    (car arglist) (cdr arglist)))
	       ((and (boolean? destination)	; string output
		     (not destination))
		(call-with-output-string
		 (lambda (port) (format:out port (car arglist) (cdr arglist)))))
	       (else
		(format:error "illegal destination `~a'" destination)))))))

       (format:out                              ; the output handler for a port
	(lambda (port fmt args)	
	  (set! format:port port)		; global port for
					; output routines
	  (set! format:case-conversion #f)	; modifier case
					; conversion procedure
	  (set! format:flush-output #f)		; ~! reset
	  (and-let* ((col (port-column port)))	; get current column from port
		    (set! format:output-col col))
	  (let ((arg-pos (format:format-work fmt args))
		(arg-len (length args)))
	    (cond
	     ((> arg-pos arg-len)
	      (set! format:arg-pos (+ arg-len 1))
	      (display format:arg-pos)
	      (format:error "~a missing argument~:p" (- arg-pos arg-len)))
	     (else
	      (if format:flush-output (force-output port))
	      #t)))))

       (format:parameter-characters
	'(#\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7 #\8 #\9 #\- #\+ #\v #\# #\'))

       (format:format-work ; does the formatting work
	(lambda (format-string arglist)
	  (letrec
	      ((format-string-len (string-length format-string))
	       (arg-pos 0)			; argument position in arglist
	       (arg-len (length arglist))	; number of arguments
	       (modifier #f)			; 'colon | 'at | 'colon-at | #f
	       (params '())			; directive parameter list
	       (param-value-found #f)		; a directive
					; parameter value
					; found
	       (conditional-nest 0)		; conditional nesting level
	       (clause-pos 0)			; last cond. clause
					; beginning char pos
	       (clause-default #f)		; conditional default
					; clause string
	       (clauses '())			; conditional clause
					; string list
	       (conditional-type #f)		; reflects the
					; contional modifiers
	       (conditional-arg #f)		; argument to apply the conditional
	       (iteration-nest 0)		; iteration nesting level
	       (iteration-pos 0)		; iteration string
					; beginning char pos
	       (iteration-type #f)		; reflects the
					; iteration modifiers
	       (max-iterations #f)		; maximum number of
					; iterations
	       (recursive-pos-save format:pos)
	       
	       (next-char			; gets the next char
					; from format-string
		(lambda ()
		  (let ((ch (peek-next-char)))
		    (set! format:pos (+ 1 format:pos))
		    ch)))
	       
	       (peek-next-char
		(lambda ()
		  (if (>= format:pos format-string-len)
		      (format:error "illegal format string")
		      (string-ref format-string format:pos))))
	       
	       (one-positive-integer?
		(lambda (params)
		  (cond
		   ((null? params) #f)
		   ((and (integer? (car params))
			 (>= (car params) 0)
			 (= (length params) 1)) #t)
		   (else
		    (format:error
		     "one positive integer parameter expected")))))
	       
	       (next-arg
		(lambda ()
		  (if (>= arg-pos arg-len)
		      (begin
			(set! format:arg-pos (+ arg-len 1))
			(format:error "missing argument(s)")))
		  (add-arg-pos 1)
		  (list-ref arglist (- arg-pos 1))))
	       
	       (prev-arg
		(lambda ()
		  (add-arg-pos -1)
		  (if (negative? arg-pos)
		      (format:error "missing backward argument(s)"))
		  (list-ref arglist arg-pos)))
	       
	       (rest-args
		(lambda ()
		  (let loop ((l arglist) (k arg-pos)) ; list-tail definition
		    (if (= k 0) l (loop (cdr l) (- k 1))))))
	       
	       (add-arg-pos
		(lambda (n) 
		  (set! arg-pos (+ n arg-pos))
		  (set! format:arg-pos arg-pos)))
	       
	       (anychar-dispatch		; dispatches the format-string
		(lambda ()
		  (if (>= format:pos format-string-len)
		      arg-pos			; used for ~? continuance
		      (let ((char (next-char)))
			(cond
			 ((char=? char #\~)
			  (set! modifier #f)
			  (set! params '())
			  (set! param-value-found #f)
			  (tilde-dispatch))
			 (else
			  (if (and (zero? conditional-nest)
				   (zero? iteration-nest))
			      (format:out-char char))
			  (anychar-dispatch)))))))
	       
	       (tilde-dispatch
		(lambda ()
		  (cond
		   ((>= format:pos format-string-len)
		    (format:out-str "~")	; tilde at end of
					; string is just
					; output
		    arg-pos)			; used for ~?
					; continuance
		   ((and (or (zero? conditional-nest)
			     (memv (peek-next-char) ; find conditional
					; directives
				   (append '(#\[ #\] #\; #\: #\@ #\^)
					   format:parameter-characters)))
			 (or (zero? iteration-nest)
			     (memv (peek-next-char) ; find iteration
					; directives
				   (append '(#\{ #\} #\: #\@ #\^)
					   format:parameter-characters))))
		    (case (char-upcase (next-char))
		      
		      ;; format directives
		      
		      ((#\A)			; Any -- for humans
		       (set! format:read-proof
			     (memq modifier '(colon colon-at)))
		       (format:out-obj-padded (memq modifier '(at colon-at))
					      (next-arg) #f params)
		       (anychar-dispatch))
		      ((#\S)			; Slashified -- for parsers
		       (set! format:read-proof
			     (memq modifier '(colon colon-at)))
		       (format:out-obj-padded (memq modifier '(at colon-at))
					      (next-arg) #t params)
		       (anychar-dispatch))
		      ((#\D)			; Decimal
		       (format:out-num-padded modifier (next-arg) params 10)
		       (anychar-dispatch))
		      ((#\X)			; Hexadecimal
		       (format:out-num-padded modifier (next-arg) params 16)
		       (anychar-dispatch))
		      ((#\O)			; Octal
		       (format:out-num-padded modifier (next-arg) params 8)
		       (anychar-dispatch))
		      ((#\B)			; Binary
		       (format:out-num-padded modifier (next-arg) params 2)
		       (anychar-dispatch))
		      ((#\R)
		       (if (null? params)
			   (format:out-obj-padded ; Roman, cardinal,
					; ordinal numerals
			    #f
			    ((case modifier
			       ((at) format:num->roman)
			       ((colon-at) format:num->old-roman)
			       ((colon) format:num->ordinal)
			       (else format:num->cardinal))
			     (next-arg))
			    #f params)
			   (format:out-num-padded ; any Radix
			    modifier (next-arg) (cdr params) (car params)))
		       (anychar-dispatch))
		      ((#\F)			; Fixed-format floating-point
		       (if format:floats
			   (format:out-fixed modifier (next-arg) params)
			   (format:out-str (number->string (next-arg))))
		       (anychar-dispatch))
		      ((#\E)			; Exponential floating-point
		       (if format:floats
			   (format:out-expon modifier (next-arg) params)
			   (format:out-str (number->string (next-arg))))
		       (anychar-dispatch))
		      ((#\G)			; General floating-point
		       (if format:floats
			   (format:out-general modifier (next-arg) params)
			   (format:out-str (number->string (next-arg))))
		       (anychar-dispatch))
		      ((#\$)			; Dollars floating-point
		       (if format:floats
			   (format:out-dollar modifier (next-arg) params)
			   (format:out-str (number->string (next-arg))))
		       (anychar-dispatch))
		      ((#\I)			; Complex numbers
		       (if (not format:complex-numbers)
			   (format:error
			    "complex numbers not supported by this scheme system"))
		       (let ((z (next-arg)))
			 (if (not (complex? z))
			     (format:error "argument not a complex number"))
			 (format:out-fixed modifier (real-part z) params)
			 (format:out-fixed 'at (imag-part z) params)
			 (format:out-char #\i))
		       (anychar-dispatch))
		      ((#\C)			; Character
		       (let ((ch (if (one-positive-integer? params)
				     (integer->char (car params))
				     (next-arg))))
			 (if (not (char? ch))
			     (format:error "~~c expects a character"))
			 (case modifier
			   ((at)
			    (format:out-str (format:char->str ch)))
			   ((colon)
			    (let ((c (char->integer ch)))
			      (if (< c 0)
				  (set! c (+ c 256))) ; compensate
					; complement
					; impl.
			      (cond
			       ((< c #x20)	; assumes that control
					; chars are < #x20
				(format:out-char #\^)
				(format:out-char
				 (integer->char (+ c #x40))))
			       ((>= c #x7f)
				(format:out-str "#\\")
				(format:out-str
				 (if format:radix-pref
				     (let ((s (number->string c 8)))
				       (substring s 2 (string-length s)))
				     (number->string c 8))))
			       (else
				(format:out-char ch)))))
			   (else (format:out-char ch))))
		       (anychar-dispatch))
		      ((#\P)			; Plural
		       (if (memq modifier '(colon colon-at))
			   (prev-arg))
		       (let ((arg (next-arg)))
			 (if (not (number? arg))
			     (format:error "~~p expects a number argument"))
			 (if (= arg 1)
			     (if (memq modifier '(at colon-at))
				 (format:out-char #\y))
			     (if (memq modifier '(at colon-at))
				 (format:out-str "ies")
				 (format:out-char #\s))))
		       (anychar-dispatch))
		      ((#\~)			; Tilde
		       (if (one-positive-integer? params)
			   (format:out-fill (car params) #\~)
			   (format:out-char #\~))
		       (anychar-dispatch))
		      ((#\%)			; Newline
		       (if (one-positive-integer? params)
			   (format:out-fill (car params) #\newline)
			   (format:out-char #\newline))
		       (set! format:output-col 0)
		       (anychar-dispatch))
		      ((#\&)			; Fresh line
		       (if (one-positive-integer? params)
			   (begin
			     (if (> (car params) 0)
				 (format:out-fill (- (car params)
						     (if (>
							  format:output-col
							  0) 0 1))
						  #\newline))
			     (set! format:output-col 0))
			   (if (> format:output-col 0)
			       (format:out-char #\newline)))
		       (anychar-dispatch))
		      ((#\_)			; Space character
		       (if (one-positive-integer? params)
			   (format:out-fill (car params) #\space)
			   (format:out-char #\space))
		       (anychar-dispatch))
		      ((#\/)			; Tabulator character
		       (if (one-positive-integer? params)
			   (format:out-fill (car params) #\tab)
			   (format:out-char #\tab))
		       (anychar-dispatch))
		      ((#\|)			; Page seperator
		       (if (one-positive-integer? params)
			   (format:out-fill (car params) #\page)
			   (format:out-char #\page))
		       (set! format:output-col 0)
		       (anychar-dispatch))
		      ((#\T)			; Tabulate
		       (format:tabulate modifier params)
		       (anychar-dispatch))
		      ((#\Y)			; Pretty-print
		       (pretty-print (next-arg) format:port)
		       (set! format:output-col 0)
		       (anychar-dispatch))
		      ((#\? #\K)		; Indirection (is "~K" in T-Scheme)
		       (cond
			((memq modifier '(colon colon-at))
			 (format:error "illegal modifier in ~~?"))
			((eq? modifier 'at)
			 (let* ((frmt (next-arg))
				(args (rest-args)))
			   (add-arg-pos (format:format-work frmt args))))
			(else
			 (let* ((frmt (next-arg))
				(args (next-arg)))
			   (format:format-work frmt args))))
		       (anychar-dispatch))
		      ((#\!)			; Flush output
		       (set! format:flush-output #t)
		       (anychar-dispatch))
		      ((#\newline)		; Continuation lines
		       (if (eq? modifier 'at)
			   (format:out-char #\newline))
		       (if (< format:pos format-string-len)
			   (do ((ch (peek-next-char) (peek-next-char)))
			       ((or (not (char-whitespace? ch))
				    (= format:pos (- format-string-len 1))))
			     (if (eq? modifier 'colon)
				 (format:out-char (next-char))
				 (next-char))))
		       (anychar-dispatch))
		      ((#\*)			; Argument jumping
		       (case modifier
			 ((colon)		; jump backwards
			  (if (one-positive-integer? params)
			      (do ((i 0 (+ i 1)))
				  ((= i (car params)))
				(prev-arg))
			      (prev-arg)))
			 ((at)			; jump absolute
			  (set! arg-pos (if (one-positive-integer? params)
					    (car params) 0)))
			 ((colon-at)
			  (format:error "illegal modifier `:@' in ~~* directive"))
			 (else			; jump forward
			  (if (one-positive-integer? params)
			      (do ((i 0 (+ i 1)))
				  ((= i (car params)))
				(next-arg))
			      (next-arg))))
		       (anychar-dispatch))
		      ((#\()			; Case conversion begin
		       (set! format:case-conversion
			     (case modifier
			       ((at) string-capitalize-first)
			       ((colon) string-capitalize)
			       ((colon-at) string-upcase)
			       (else string-downcase)))
		       (anychar-dispatch))
		      ((#\))			; Case conversion end
		       (if (not format:case-conversion)
			   (format:error "missing ~~("))
		       (set! format:case-conversion #f)
		       (anychar-dispatch))
		      ((#\[)			; Conditional begin
		       (set! conditional-nest (+ conditional-nest 1))
		       (cond
			((= conditional-nest 1)
			 (set! clause-pos format:pos)
			 (set! clause-default #f)
			 (set! clauses '())
			 (set! conditional-type
			       (case modifier
				 ((at) 'if-then)
				 ((colon) 'if-else-then)
				 ((colon-at) (format:error "illegal modifier in ~~["))
				 (else 'num-case)))
			 (set! conditional-arg
			       (if (one-positive-integer? params)
				   (car params)
				   (next-arg)))))
		       (anychar-dispatch))
		      ((#\;)                    ; Conditional separator
		       (if (zero? conditional-nest)
			   (format:error "~~; not in ~~[~~] conditional"))
		       (if (not (null? params))
			   (format:error "no parameter allowed in ~~;"))
		       (if (= conditional-nest 1)
			   (let ((clause-str
				  (cond
				   ((eq? modifier 'colon)
				    (set! clause-default #t)
				    (substring format-string clause-pos 
					       (- format:pos 3)))
				   ((memq modifier '(at colon-at))
				    (format:error "illegal modifier in ~~;"))
				   (else
				    (substring format-string clause-pos
					       (- format:pos 2))))))
			     (set! clauses (append clauses (list clause-str)))
			     (set! clause-pos format:pos)))
		       (anychar-dispatch))
		      ((#\])			; Conditional end
		       (if (zero? conditional-nest) (format:error "missing ~~["))
		       (set! conditional-nest (- conditional-nest 1))
		       (if modifier
			   (format:error "no modifier allowed in ~~]"))
		       (if (not (null? params))
			   (format:error "no parameter allowed in ~~]"))
		       (cond
			((zero? conditional-nest)
			 (let ((clause-str (substring format-string clause-pos
						      (- format:pos 2))))
			   (if clause-default
			       (set! clause-default clause-str)
			       (set! clauses (append clauses (list clause-str)))))
			 (case conditional-type
			   ((if-then)
			    (if conditional-arg
				(format:format-work (car clauses)
						    (list conditional-arg))))
			   ((if-else-then)
			    (add-arg-pos
			     (format:format-work (if conditional-arg
						     (cadr clauses)
						     (car clauses))
						 (rest-args))))
			   ((num-case)
			    (if (or (not (integer? conditional-arg))
				    (< conditional-arg 0))
				(format:error "argument not a positive integer"))
			    (if (not (and (>= conditional-arg (length clauses))
					  (not clause-default)))
				(add-arg-pos
				 (format:format-work
				  (if (>= conditional-arg (length clauses))
				      clause-default
				      (list-ref clauses conditional-arg))
				  (rest-args))))))))
		       (anychar-dispatch))
		      ((#\{)			; Iteration begin
		       (set! iteration-nest (+ iteration-nest 1))
		       (cond
			((= iteration-nest 1)
			 (set! iteration-pos format:pos)
			 (set! iteration-type
			       (case modifier
				 ((at) 'rest-args)
				 ((colon) 'sublists)
				 ((colon-at) 'rest-sublists)
				 (else 'list)))
			 (set! max-iterations (if (one-positive-integer? params)
						  (car params) #f))))
		       (anychar-dispatch))
		      ((#\})			; Iteration end
		       (if (zero? iteration-nest) (format:error "missing ~~{"))
		       (set! iteration-nest (- iteration-nest 1))
		       (case modifier
			 ((colon)
			  (if (not max-iterations) (set! max-iterations 1)))
			 ((colon-at at) (format:error "illegal modifier")))
		       (if (not (null? params))
			   (format:error "no parameters allowed in ~~}"))
		       (if (zero? iteration-nest)
			   (let ((iteration-str
				  (substring format-string iteration-pos
					     (- format:pos (if modifier 3 2)))))
			     (if (string=? iteration-str "")
				 (set! iteration-str (next-arg)))
			     (case iteration-type
			       ((list)
				(let ((args (next-arg))
				      (args-len 0))
				  (if (not (list? args))
				      (format:error "expected a list argument"))
				  (set! args-len (length args))
				  (do ((arg-pos 0 (+ arg-pos
						     (format:format-work
						      iteration-str
						      (list-tail args arg-pos))))
				       (i 0 (+ i 1)))
				      ((or (>= arg-pos args-len)
					   (and max-iterations
						(>= i max-iterations)))))))
			       ((sublists)
				(let ((args (next-arg))
				      (args-len 0))
				  (if (not (list? args))
				      (format:error "expected a list argument"))
				  (set! args-len (length args))
				  (do ((arg-pos 0 (+ arg-pos 1)))
				      ((or (>= arg-pos args-len)
					   (and max-iterations
						(>= arg-pos max-iterations))))
				    (let ((sublist (list-ref args arg-pos)))
				      (if (not (list? sublist))
					  (format:error
					   "expected a list of lists argument"))
				      (format:format-work iteration-str sublist)))))
			       ((rest-args)
				(let* ((args (rest-args))
				       (args-len (length args))
				       (usedup-args
					(do ((arg-pos 0 (+ arg-pos
							   (format:format-work
							    iteration-str
							    (list-tail
							     args arg-pos))))
					     (i 0 (+ i 1)))
					    ((or (>= arg-pos args-len)
						 (and max-iterations
						      (>= i max-iterations)))
					     arg-pos))))
				  (add-arg-pos usedup-args)))
			       ((rest-sublists)
				(let* ((args (rest-args))
				       (args-len (length args))
				       (usedup-args
					(do ((arg-pos 0 (+ arg-pos 1)))
					    ((or (>= arg-pos args-len)
						 (and max-iterations
						      (>= arg-pos max-iterations)))
					     arg-pos)
					  (let ((sublist (list-ref args arg-pos)))
					    (if (not (list? sublist))
						(format:error "expected list arguments"))
					    (format:format-work iteration-str sublist)))))
				  (add-arg-pos usedup-args)))
			       (else (format:error "internal error in ~~}")))))
		       (anychar-dispatch))
		      ((#\^)			; Up and out
		       (let* ((continue
			       (cond
				((not (null? params))
				 (not
				  (case (length params)
				    ((1) (zero? (car params)))
				    ((2) (= (list-ref params 0) (list-ref params 1)))
				    ((3) (<= (list-ref params 0)
					     (list-ref params 1)
					     (list-ref params 2)))
				    (else (format:error "too much parameters")))))
				(format:case-conversion ; if conversion stop conversion
				 (set! format:case-conversion string-copy) #t)
				((= iteration-nest 1) #t)
				((= conditional-nest 1) #t)
				((>= arg-pos arg-len)
				 (set! format:pos format-string-len) #f)
				(else #t))))
			 (if continue
			     (anychar-dispatch))))

		      ;; format directive modifiers and parameters

		      ((#\@)			; `@' modifier
		       (if (memq modifier '(at colon-at))
			   (format:error "double `@' modifier"))
		       (set! modifier (if (eq? modifier 'colon) 'colon-at 'at))
		       (tilde-dispatch))
		      ((#\:)			; `:' modifier
		       (if (memq modifier '(colon colon-at))
			   (format:error "double `:' modifier"))
		       (set! modifier (if (eq? modifier 'at) 'colon-at 'colon))
		       (tilde-dispatch))
		      ((#\')			; Character parameter
		       (if modifier (format:error "misplaced modifier"))
		       (set! params (append params (list (char->integer (next-char)))))
		       (set! param-value-found #t)
		       (tilde-dispatch))
		      ((#\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7 #\8 #\9 #\- #\+) ; num. paramtr
		       (if modifier (format:error "misplaced modifier"))
		       (let ((num-str-beg (- format:pos 1))
			     (num-str-end format:pos))
			 (do ((ch (peek-next-char) (peek-next-char)))
			     ((not (char-numeric? ch)))
			   (next-char)
			   (set! num-str-end (+ 1 num-str-end)))
			 (set! params
			       (append params
				       (list (string->number
					      (substring format-string
							 num-str-beg
							 num-str-end))))))
		       (set! param-value-found #t)
		       (tilde-dispatch))
		      ((#\V)			; Variable parameter from next argum.
		       (if modifier (format:error "misplaced modifier"))
		       (set! params (append params (list (next-arg))))
		       (set! param-value-found #t)
		       (tilde-dispatch))
		      ((#\#)			; Parameter is number of remaining args
		       (if param-value-found (format:error "misplaced '#'"))
		       (if modifier (format:error "misplaced modifier"))
		       (set! params (append params (list (length (rest-args)))))
		       (set! param-value-found #t)
		       (tilde-dispatch))
		      ((#\,)			; Parameter separators
		       (if modifier (format:error "misplaced modifier"))
		       (if (not param-value-found)
			   (set! params (append params '(#f)))) ; append empty paramtr
		       (set! param-value-found #f)
		       (tilde-dispatch))
		      ((#\Q)			; Inquiry messages
		       (if (eq? modifier 'colon)
			   (format:out-str format:version)
			   (let ((nl (string #\newline)))
			     (format:out-str
			      (string-append
			       "SLIB Common LISP format version " format:version nl
			       "  (C) copyright 1992-1994 by Dirk Lutzebaeck" nl
			       "  please send bug reports to `lutzeb@cs.tu-berlin.de'"
			       nl))))
		       (anychar-dispatch))
		      (else			; Unknown tilde directive
		       (format:error "unknown control character `~c'"
				     (string-ref format-string (- format:pos 1))))))
		   (else (anychar-dispatch)))))) ; in case of conditional

	    (set! format:pos 0)
	    (set! format:arg-pos 0)
	    (anychar-dispatch)			; start the formatting
	    (set! format:pos recursive-pos-save)
	    arg-pos)))				; return the position in the arg. list

       ;; when format:read-proof is true, format:obj->str will wrap
       ;; result strings starting with "#<" in an extra pair of double
       ;; quotes.
       
       (format:read-proof #f)

       ;; format:obj->str returns a R4RS representation as a string of
       ;; an arbitrary scheme object.

       (format:obj->str
	(lambda (obj slashify)
	  (let ((res (if slashify
			 (object->string obj)
			 (with-output-to-string (lambda () (display obj))))))
	    (if (and format:read-proof (string-prefix? "#<" res))
		(object->string res)
		res))))

       ;; format:char->str converts a character into a slashified string as
       ;; done by `write'. The procedure is dependent on the integer
       ;; representation of characters and assumes a character number according to
       ;; the ASCII character set.

       (format:char->str
	(lambda (ch)
	  (let ((int-rep (char->integer ch)))
	    (if (< int-rep 0)			; if chars are [-128...+127]
		(set! int-rep (+ int-rep 256)))
	    (string-append
	     "#\\"
	     (cond
	      ((char=? ch #\newline) "newline")
	      ((and (>= int-rep 0) (<= int-rep 32))
	       (vector-ref format:ascii-non-printable-charnames int-rep))
	      ((= int-rep 127) "del")
	      ((>= int-rep 128)		; octal representation
	       (if format:radix-pref
		   (let ((s (number->string int-rep 8)))
		     (substring s 2 (string-length s)))
		   (number->string int-rep 8)))
	      (else (string ch)))))))

       (format:space-ch (char->integer #\space))
       (format:zero-ch (char->integer #\0))

       (format:par
	(lambda (pars length index default name)
	  (if (> length index)
	      (let ((par (list-ref pars index)))
		(if par
		    (if name
			(if (< par 0)
			    (format:error 
			     "~s parameter must be a positive integer" name)
			    par)
			par)
		    default))
	      default)))

       (format:out-obj-padded
	(lambda (pad-left obj slashify pars)
	       (if (null? pars)
		   (format:out-str (format:obj->str obj slashify))
		   (let ((l (length pars)))
		     (let ((mincol (format:par pars l 0 0 "mincol"))
			   (colinc (format:par pars l 1 1 "colinc"))
			   (minpad (format:par pars l 2 0 "minpad"))
			   (padchar (integer->char
				     (format:par pars l 3 format:space-ch #f)))
			   (objstr (format:obj->str obj slashify)))
		       (if (not pad-left)
			   (format:out-str objstr))
		       (do ((objstr-len (string-length objstr))
			    (i minpad (+ i colinc)))
			   ((>= (+ objstr-len i) mincol)
			    (format:out-fill i padchar)))
		       (if pad-left
			   (format:out-str objstr)))))))

       (format:out-num-padded
	(lambda (modifier number pars radix)
	  (if (not (integer? number)) (format:error "argument not an integer"))
	  (let ((numstr (number->string number radix)))
	    (if (and format:radix-pref (not (= radix 10)))
		(set! numstr (substring numstr 2 (string-length numstr))))
	    (if (and (null? pars) (not modifier))
		(format:out-str numstr)
		(let ((l (length pars))
		      (numstr-len (string-length numstr)))
		  (let ((mincol (format:par pars l 0 #f "mincol"))
			(padchar (integer->char
				  (format:par pars l 1 format:space-ch #f)))
			(commachar (integer->char
				    (format:par pars l 2 (char->integer #\,) #f)))
			(commawidth (format:par pars l 3 3 "commawidth")))
		    (if mincol
			(let ((numlen numstr-len)) ; calc. the output len of number
			  (if (and (memq modifier '(at colon-at)) (>= number 0))
			      (set! numlen (+ numlen 1)))
			  (if (memq modifier '(colon colon-at))
			      (set! numlen (+ (quotient (- numstr-len 
							   (if (< number 0) 2 1))
							commawidth)
					      numlen)))
			  (if (> mincol numlen)
			      (format:out-fill (- mincol numlen) padchar))))
		    (if (and (memq modifier '(at colon-at))
			     (>= number 0))
			(format:out-char #\+))
		    (if (memq modifier '(colon colon-at)) ; insert comma character
			(let ((start (remainder numstr-len commawidth))
			      (ns (if (< number 0) 1 0)))
			  (format:out-substr numstr 0 start)
			  (do ((i start (+ i commawidth)))
			      ((>= i numstr-len))
			    (if (> i ns)
				(format:out-char commachar))
			    (format:out-substr numstr i (+ i commawidth))))
			(format:out-str numstr))))))))

       (format:tabulate
	(lambda (modifier pars)
	  (let ((l (length pars)))
	    (let ((colnum (format:par pars l 0 1 "colnum"))
		  (colinc (format:par pars l 1 1 "colinc"))
		  (padch (integer->char (format:par pars l 2 format:space-ch #f))))
	      (case modifier
		((colon colon-at)
		 (format:error "unsupported modifier for ~~t"))
		((at)				; relative tabulation
		 (format:out-fill
		  (if (= colinc 0)
		      colnum			; colnum = colrel
		      (do ((c 0 (+ c colinc))
			   (col (+ format:output-col colnum)))
			  ((>= c col)
			   (- c format:output-col))))
		  padch))
		(else				; absolute tabulation
		 (format:out-fill
		  (cond
		   ((< format:output-col colnum)
		    (- colnum format:output-col))
		   ((= colinc 0)
		    0)
		   (else
		    (do ((c colnum (+ c colinc)))
			((>= c format:output-col)
			 (- c format:output-col)))))
		  padch)))))))


       ;; roman numerals (from dorai@cs.rice.edu).

       (format:roman-alist
	'((1000 #\M) (500 #\D) (100 #\C) (50 #\L)
	  (10 #\X) (5 #\V) (1 #\I)))

       (format:roman-boundary-values
	'(100 100 10 10 1 1 #f))

       (format:num->old-roman
	(lambda (n)
	  (if (and (integer? n) (>= n 1))
	      (let loop ((n n)
			 (romans format:roman-alist)
			 (s '()))
		(if (null? romans) (list->string (reverse s))
		    (let ((roman-val (caar romans))
			  (roman-dgt (cadar romans)))
		      (do ((q (quotient n roman-val) (- q 1))
			   (s s (cons roman-dgt s)))
			  ((= q 0)
			   (loop (remainder n roman-val)
				 (cdr romans) s))))))
	      (format:error "only positive integers can be romanized"))))

       (format:num->roman
	(lambda (n)
	  (if (and (integer? n) (> n 0))
	      (let loop ((n n)
			 (romans format:roman-alist)
			 (boundaries format:roman-boundary-values)
			 (s '()))
		(if (null? romans)
		    (list->string (reverse s))
		    (let ((roman-val (caar romans))
			  (roman-dgt (cadar romans))
			  (bdry (car boundaries)))
		      (let loop2 ((q (quotient n roman-val))
				  (r (remainder n roman-val))
				  (s s))
			(if (= q 0)
			    (if (and bdry (>= r (- roman-val bdry)))
				(loop (remainder r bdry) (cdr romans)
				      (cdr boundaries)
				      (cons roman-dgt
					    (append
					     (cdr (assv bdry romans))
					     s)))
				(loop r (cdr romans) (cdr boundaries) s))
			    (loop2 (- q 1) r (cons roman-dgt s)))))))
	      (format:error "only positive integers can be romanized"))))

       ;; cardinals & ordinals (from dorai@cs.rice.edu)

       (format:cardinal-ones-list
	'(#f "one" "two" "three" "four" "five"
	     "six" "seven" "eight" "nine" "ten" "eleven" "twelve" "thirteen"
	     "fourteen" "fifteen" "sixteen" "seventeen" "eighteen"
	     "nineteen"))

       (format:cardinal-tens-list
	'(#f #f "twenty" "thirty" "forty" "fifty" "sixty" "seventy" "eighty"
	     "ninety"))

       (format:num->cardinal999
	(lambda (n)
					;this procedure is inspired by the Bruno Haible's CLisp
					;function format-small-cardinal, which converts numbers
					;in the range 1 to 999, and is used for converting each
					;thousand-block in a larger number
	  (let* ((hundreds (quotient n 100))
		 (tens+ones (remainder n 100))
		 (tens (quotient tens+ones 10))
		 (ones (remainder tens+ones 10)))
	    (append
	     (if (> hundreds 0)
		 (append
		  (string->list
		   (list-ref format:cardinal-ones-list hundreds))
		  (string->list" hundred")
		  (if (> tens+ones 0) '(#\space) '()))
		 '())
	     (if (< tens+ones 20)
		 (if (> tens+ones 0)
		     (string->list
		      (list-ref format:cardinal-ones-list tens+ones))
		     '())
		 (append
		  (string->list
		   (list-ref format:cardinal-tens-list tens))
		  (if (> ones 0)
		      (cons #\-
			    (string->list
			     (list-ref format:cardinal-ones-list ones)))
		      '())))))))

       (format:cardinal-thousand-block-list
	'("" " thousand" " million" " billion" " trillion" " quadrillion"
	  " quintillion" " sextillion" " septillion" " octillion" " nonillion"
	  " decillion" " undecillion" " duodecillion" " tredecillion"
	  " quattuordecillion" " quindecillion" " sexdecillion" " septendecillion"
	  " octodecillion" " novemdecillion" " vigintillion"))

       (format:num->cardinal
	(lambda (n)
	  (cond ((not (integer? n))
		 (format:error
		  "only integers can be converted to English cardinals"))
		((= n 0) "zero")
		((< n 0) (string-append "minus " (format:num->cardinal (- n))))
		(else
		 (let ((power3-word-limit
			(length format:cardinal-thousand-block-list)))
		   (let loop ((n n)
			      (power3 0)
			      (s '()))
		     (if (= n 0)
			 (list->string s)
			 (let ((n-before-block (quotient n 1000))
			       (n-after-block (remainder n 1000)))
			   (loop n-before-block
				 (+ power3 1)
				 (if (> n-after-block 0)
				     (append
				      (if (> n-before-block 0)
					  (string->list ", ") '())
				      (format:num->cardinal999 n-after-block)
				      (if (< power3 power3-word-limit)
					  (string->list
					   (list-ref
					    format:cardinal-thousand-block-list
					    power3))
					  (append
					   (string->list " times ten to the ")
					   (string->list
					    (format:num->ordinal
					     (* power3 3)))
					   (string->list " power")))
				      s)
				     s))))))))))

       (format:ordinal-ones-list
	'(#f "first" "second" "third" "fourth" "fifth"
	     "sixth" "seventh" "eighth" "ninth" "tenth" "eleventh" "twelfth"
	     "thirteenth" "fourteenth" "fifteenth" "sixteenth" "seventeenth"
	     "eighteenth" "nineteenth"))

       (format:ordinal-tens-list
	'(#f #f "twentieth" "thirtieth" "fortieth" "fiftieth" "sixtieth"
	     "seventieth" "eightieth" "ninetieth"))

       (format:num->ordinal
	(lambda (n)
	  (cond ((not (integer? n))
		 (format:error
		  "only integers can be converted to English ordinals"))
		((= n 0) "zeroth")
		((< n 0) (string-append "minus " (format:num->ordinal (- n))))
		(else
		 (let ((hundreds (quotient n 100))
		       (tens+ones (remainder n 100)))
		   (string-append
		    (if (> hundreds 0)
			(string-append
			 (format:num->cardinal (* hundreds 100))
			 (if (= tens+ones 0) "th" " "))
			"")
		    (if (= tens+ones 0) ""
			(if (< tens+ones 20)
			    (list-ref format:ordinal-ones-list tens+ones)
			    (let ((tens (quotient tens+ones 10))
				  (ones (remainder tens+ones 10)))
			      (if (= ones 0)
				  (list-ref format:ordinal-tens-list tens)
				  (string-append
				   (list-ref format:cardinal-tens-list tens)
				   "-"
				   (list-ref format:ordinal-ones-list ones))))
			    ))))))))

       ;; format inf and nan.

       (format:out-inf-nan
	(lambda (number width digits edigits overch padch)
	  ;; inf and nan are always printed exactly as "+inf.0", "-inf.0" or
	  ;; "+nan.0", suitably justified in their field.  We insist on
	  ;; printing this exact form so that the numbers can be read back in.

	  (let* ((str (number->string number))
		 (len (string-length str))
		 (dot (string-index str #\.))
		 (digits (+ (or digits 0)
			    (if edigits (+ edigits 2) 0))))
	    (if (and width overch (< width len))
		(format:out-fill width (integer->char overch))
		(let* ((leftpad (if width
				    (max (- width (max len (+ dot 1 digits))) 0)
				    0))
		       (rightpad (if width
				     (max (- width leftpad len) 0)
				     0))
		       (padch (integer->char (or padch format:space-ch)))) 
		  (format:out-fill leftpad padch)
		  (format:out-str str)
		  (format:out-fill rightpad padch))))))

       ;; format fixed flonums (~F)

       (format:out-fixed
	(lambda (modifier number pars)
	  (if (not (or (number? number) (string? number)))
	      (format:error "argument is not a number or a number string"))

	  (let ((l (length pars)))
	    (let ((width (format:par pars l 0 #f "width"))
		  (digits (format:par pars l 1 #f "digits"))
		  (scale (format:par pars l 2 0 #f))
		  (overch (format:par pars l 3 #f #f))
		  (padch (format:par pars l 4 format:space-ch #f)))

	      (cond
	       ((or (inf? number) (nan? number))
		(format:out-inf-nan number width digits #f overch padch))

	       (digits
		(format:parse-float 
		 (if (string? number) number (number->string number)) #t scale)
		(if (<= (- format:fn-len format:fn-dot) digits)
		    (format:fn-zfill #f (- digits (- format:fn-len format:fn-dot)))
		    (format:fn-round digits))
		(if width
		    (let ((numlen (+ format:fn-len 1)))
		      (if (or (not format:fn-pos?) (eq? modifier 'at))
			  (set! numlen (+ numlen 1)))
		      (if (and (= format:fn-dot 0) (> width (+ digits 1)))
			  (set! numlen (+ numlen 1)))
		      (if (< numlen width)
			  (format:out-fill (- width numlen) (integer->char padch)))
		      (if (and overch (> numlen width))
			  (format:out-fill width (integer->char overch))
			  (format:fn-out modifier (> width (+ digits 1)))))
		    (format:fn-out modifier #t)))

	       (else
		(format:parse-float
		 (if (string? number) number (number->string number)) #t scale)
		(format:fn-strip)
		(if width
		    (let ((numlen (+ format:fn-len 1)))
		      (if (or (not format:fn-pos?) (eq? modifier 'at))
			  (set! numlen (+ numlen 1)))
		      (if (= format:fn-dot 0)
			  (set! numlen (+ numlen 1)))
		      (if (< numlen width)
			  (format:out-fill (- width numlen) (integer->char padch)))
		      (if (> numlen width)	; adjust precision if possible
			  (let ((dot-index (- numlen
					      (- format:fn-len format:fn-dot))))
			    (if (> dot-index width)
				(if overch	; numstr too big for required width
				    (format:out-fill width (integer->char overch))
				    (format:fn-out modifier #t))
				(begin
				  (format:fn-round (- width dot-index))
				  (format:fn-out modifier #t))))
			  (format:fn-out modifier #t)))
		    (format:fn-out modifier #t))))))))

       ;; format exponential flonums (~E)

       (format:out-expon
	(lambda (modifier number pars)
	  (if (not (or (number? number) (string? number)))
	      (format:error "argument is not a number"))

	  (let ((l (length pars)))
	    (let ((width (format:par pars l 0 #f "width"))
		  (digits (format:par pars l 1 #f "digits"))
		  (edigits (format:par pars l 2 #f "exponent digits"))
		  (scale (format:par pars l 3 1 #f))
		  (overch (format:par pars l 4 #f #f))
		  (padch (format:par pars l 5 format:space-ch #f))
		  (expch (format:par pars l 6 #f #f)))
	      
	      (cond
	       ((or (inf? number) (nan? number))
		(format:out-inf-nan number width digits edigits overch padch))

	       (digits				; fixed precision

		(let ((digits (if (> scale 0)
				  (if (< scale (+ digits 2))
				      (+ (- digits scale) 1)
				      0)
				  digits)))
		  (format:parse-float 
		   (if (string? number) number (number->string number)) #f scale)
		  (if (<= (- format:fn-len format:fn-dot) digits)
		      (format:fn-zfill #f (- digits (- format:fn-len format:fn-dot)))
		      (format:fn-round digits))
		  (if width
		      (if (and edigits overch (> format:en-len edigits))
			  (format:out-fill width (integer->char overch))
			  (let ((numlen (+ format:fn-len 3))) ; .E+
			    (if (or (not format:fn-pos?) (eq? modifier 'at))
				(set! numlen (+ numlen 1)))
			    (if (and (= format:fn-dot 0) (> width (+ digits 1)))
				(set! numlen (+ numlen 1)))	
			    (set! numlen
				  (+ numlen 
				     (if (and edigits (>= edigits format:en-len))
					 edigits 
					 format:en-len)))
			    (if (< numlen width)
				(format:out-fill (- width numlen)
						 (integer->char padch)))
			    (if (and overch (> numlen width))
				(format:out-fill width (integer->char overch))
				(begin
				  (format:fn-out modifier (> width (- numlen 1)))
				  (format:en-out edigits expch)))))
		      (begin
			(format:fn-out modifier #t)
			(format:en-out edigits expch)))))

	       (else
		(format:parse-float
		 (if (string? number) number (number->string number)) #f scale)
		(format:fn-strip)
		(if width
		    (if (and edigits overch (> format:en-len edigits))
			(format:out-fill width (integer->char overch))
			(let ((numlen (+ format:fn-len 3))) ; .E+
			  (if (or (not format:fn-pos?) (eq? modifier 'at))
			      (set! numlen (+ numlen 1)))
			  (if (= format:fn-dot 0)
			      (set! numlen (+ numlen 1)))
			  (set! numlen
				(+ numlen
				   (if (and edigits (>= edigits format:en-len))
				       edigits 
				       format:en-len)))
			  (if (< numlen width)
			      (format:out-fill (- width numlen)
					       (integer->char padch)))
			  (if (> numlen width) ; adjust precision if possible
			      (let ((f (- format:fn-len format:fn-dot))) ; fract len
				(if (> (- numlen f) width)
				    (if overch ; numstr too big for required width
					(format:out-fill width 
							 (integer->char overch))
					(begin
					  (format:fn-out modifier #t)
					  (format:en-out edigits expch)))
				    (begin
				      (format:fn-round (+ (- f numlen) width))
				      (format:fn-out modifier #t)
				      (format:en-out edigits expch))))
			      (begin
				(format:fn-out modifier #t)
				(format:en-out edigits expch)))))
		    (begin
		      (format:fn-out modifier #t)
		      (format:en-out edigits expch)))))))))
       
       ;; format general flonums (~G)

       (format:out-general
	(lambda (modifier number pars)
	  (if (not (or (number? number) (string? number)))
	      (format:error "argument is not a number or a number string"))

	  (let ((l (length pars)))
	    (let ((width (if (> l 0) (list-ref pars 0) #f))
		  (digits (if (> l 1) (list-ref pars 1) #f))
		  (edigits (if (> l 2) (list-ref pars 2) #f))
		  (overch (if (> l 4) (list-ref pars 4) #f))
		  (padch (if (> l 5) (list-ref pars 5) #f)))
	      (cond
	       ((or (inf? number) (nan? number))
		;; FIXME: this isn't right.
		(format:out-inf-nan number width digits edigits overch padch))
	       (else
		(format:parse-float
		 (if (string? number) number (number->string number)) #t 0)
		(format:fn-strip)
		(let* ((ee (if edigits (+ edigits 2) 4)) ; for the following algorithm
		       (ww (if width (- width ee) #f))   ; see Steele's CL book p.395
		       (n (if (= format:fn-dot 0)	; number less than (abs 1.0) ?
			      (- (format:fn-zlead))
			      format:fn-dot))
		       (d (if digits
			      digits
			      (max format:fn-len (min n 7)))) ; q = format:fn-len
		       (dd (- d n)))
		  (if (<= 0 dd d)
		      (begin
			(format:out-fixed modifier number (list ww dd #f overch padch))
			(format:out-fill ee #\space)) ;~@T not implemented yet
		      (format:out-expon modifier number pars)))))))))

       ;; format dollar flonums (~$)

       (format:out-dollar
	(lambda (modifier number pars)
	  (if (not (or (number? number) (string? number)))
	      (format:error "argument is not a number or a number string"))

	  (let ((l (length pars)))
	    (let ((digits (format:par pars l 0 2 "digits"))
		  (mindig (format:par pars l 1 1 "mindig"))
		  (width (format:par pars l 2 0 "width"))
		  (padch (format:par pars l 3 format:space-ch #f)))

	      (cond
	       ((or (inf? number) (nan? number))
		(format:out-inf-nan number width digits #f #f padch))

	       (else
		(format:parse-float
		 (if (string? number) number (number->string number)) #t 0)
		(if (<= (- format:fn-len format:fn-dot) digits)
		    (format:fn-zfill #f (- digits (- format:fn-len format:fn-dot)))
		    (format:fn-round digits))
		(let ((numlen (+ format:fn-len 1)))
		  (if (or (not format:fn-pos?) (memq modifier '(at colon-at)))
		      (set! numlen (+ numlen 1)))
		  (if (and mindig (> mindig format:fn-dot))
		      (set! numlen (+ numlen (- mindig format:fn-dot))))
		  (if (and (= format:fn-dot 0) (not mindig))
		      (set! numlen (+ numlen 1)))
		  (if (< numlen width)
		      (case modifier
			((colon)
			 (if (not format:fn-pos?)
			     (format:out-char #\-))
			 (format:out-fill (- width numlen) (integer->char padch)))
			((at)
			 (format:out-fill (- width numlen) (integer->char padch))
			 (format:out-char (if format:fn-pos? #\+ #\-)))
			((colon-at)
			 (format:out-char (if format:fn-pos? #\+ #\-))
			 (format:out-fill (- width numlen) (integer->char padch)))
			(else
			 (format:out-fill (- width numlen) (integer->char padch))
			 (if (not format:fn-pos?)
			     (format:out-char #\-))))
		      (if format:fn-pos?
			  (if (memq modifier '(at colon-at)) (format:out-char #\+))
			  (format:out-char #\-))))
		(if (and mindig (> mindig format:fn-dot))
		    (format:out-fill (- mindig format:fn-dot) #\0))
		(if (and (= format:fn-dot 0) (not mindig))
		    (format:out-char #\0))
		(format:out-substr format:fn-str 0 format:fn-dot)
		(format:out-char #\.)
		(format:out-substr format:fn-str format:fn-dot format:fn-len)))))))

					; the flonum buffers

       (format:fn-max 400)		; max. number of number digits
       (format:fn-str #f) ; number buffer
       (format:fn-len 0)		; digit length of number
       (format:fn-dot #f)		; dot position of number
       (format:fn-pos? #t)		; number positive?
       (format:en-max 10)		; max. number of exponent digits
       (format:en-str #f) ; exponent buffer
       (format:en-len 0)		; digit length of exponent
       (format:en-pos? #t)		; exponent positive?

       (format:parse-float
	(lambda (num-str fixed? scale)
		 (set! format:fn-pos? #t)
		 (set! format:fn-len 0)
		 (set! format:fn-dot #f)
		 (set! format:en-pos? #t)
		 (set! format:en-len 0)
		 (do ((i 0 (+ i 1))
		      (left-zeros 0)
		      (mantissa? #t)
		      (all-zeros? #t)
		      (num-len (string-length num-str))
		      (c #f))			; current exam. character in num-str
		     ((= i num-len)
		      (if (not format:fn-dot)
			  (set! format:fn-dot format:fn-len))

		      (if all-zeros?
			  (begin
			    (set! left-zeros 0)
			    (set! format:fn-dot 0)
			    (set! format:fn-len 1)))

		      ;; now format the parsed values according to format's need

		      (if fixed?

			  (begin			; fixed format m.nnn or .nnn
			    (if (and (> left-zeros 0) (> format:fn-dot 0))
				(if (> format:fn-dot left-zeros) 
				    (begin		; norm 0{0}nn.mm to nn.mm
				      (format:fn-shiftleft left-zeros)
				      (set! format:fn-dot (- format:fn-dot left-zeros))
				      (set! left-zeros 0))
				    (begin		; normalize 0{0}.nnn to .nnn
				      (format:fn-shiftleft format:fn-dot)
				      (set! left-zeros (- left-zeros format:fn-dot))
				      (set! format:fn-dot 0))))
			    (if (or (not (= scale 0)) (> format:en-len 0))
				(let ((shift (+ scale (format:en-int))))
				  (cond
				   (all-zeros? #t)
				   ((> (+ format:fn-dot shift) format:fn-len)
				    (format:fn-zfill
				     #f (- shift (- format:fn-len format:fn-dot)))
				    (set! format:fn-dot format:fn-len))
				   ((< (+ format:fn-dot shift) 0)
				    (format:fn-zfill #t (- (- shift) format:fn-dot))
				    (set! format:fn-dot 0))
				   (else
				    (if (> left-zeros 0)
					(if (<= left-zeros shift) ; shift always > 0 here
					    (format:fn-shiftleft shift) ; shift out 0s
					    (begin
					      (format:fn-shiftleft left-zeros)
					      (set! format:fn-dot (- shift left-zeros))))
					(set! format:fn-dot (+ format:fn-dot shift))))))))

			  (let ((negexp		; expon format m.nnnEee
				 (if (> left-zeros 0)
				     (- left-zeros format:fn-dot -1)
				     (if (= format:fn-dot 0) 1 0))))
			    (if (> left-zeros 0)
				(begin			; normalize 0{0}.nnn to n.nn
				  (format:fn-shiftleft left-zeros)
				  (set! format:fn-dot 1))
				(if (= format:fn-dot 0)
				    (set! format:fn-dot 1)))
			    (format:en-set (- (+ (- format:fn-dot scale) (format:en-int))
					      negexp))
			    (cond 
			     (all-zeros?
			      (format:en-set 0)
			      (set! format:fn-dot 1))
			     ((< scale 0)		; leading zero
			      (format:fn-zfill #t (- scale))
			      (set! format:fn-dot 0))
			     ((> scale format:fn-dot)
			      (format:fn-zfill #f (- scale format:fn-dot))
			      (set! format:fn-dot scale))
			     (else
			      (set! format:fn-dot scale)))))
		      #t)

		   ;; do body      
		   (set! c (string-ref num-str i))	; parse the output of number->string
		   (cond				; which can be any valid number
		    ((char-numeric? c)			; representation of R4RS except 
		     (if mantissa?			; complex numbers
			 (begin
			   (if (char=? c #\0)
			       (if all-zeros?
				   (set! left-zeros (+ left-zeros 1)))
			       (begin
				 (set! all-zeros? #f)))
			   (string-set! format:fn-str format:fn-len c)
			   (set! format:fn-len (+ format:fn-len 1)))
			 (begin
			   (string-set! format:en-str format:en-len c)
			   (set! format:en-len (+ format:en-len 1)))))
		    ((or (char=? c #\-) (char=? c #\+))
		     (if mantissa?
			 (set! format:fn-pos? (char=? c #\+))
			 (set! format:en-pos? (char=? c #\+))))
		    ((char=? c #\.)
		     (set! format:fn-dot format:fn-len))
		    ((char=? c #\e)
		     (set! mantissa? #f))
		    ((char=? c #\E)
		     (set! mantissa? #f))
		    ((char-whitespace? c) #t)
		    ((char=? c #\d) #t)		; decimal radix prefix
		    ((char=? c #\#) #t)
		    (else
		     (format:error "illegal character `~c' in number->string" c))))))

       (format:en-int
	(lambda ()			; convert exponent string to integer
	  (if (= format:en-len 0)
	      0
	      (do ((i 0 (+ i 1))
		   (n 0))
		  ((= i format:en-len) 
		   (if format:en-pos?
		       n
		       (- n)))
		(set! n (+ (* n 10) (- (char->integer (string-ref format:en-str i))
				       format:zero-ch)))))))

       (format:en-set          ; set exponent string number
	(lambda (en)		
	  (set! format:en-len 0)
	  (set! format:en-pos? (>= en 0))
	  (let ((en-str (number->string en)))
	    (do ((i 0 (+ i 1))
		 (en-len (string-length en-str))
		 (c #f))
		((= i en-len))
	      (set! c (string-ref en-str i))
	      (if (char-numeric? c)
		  (begin
		    (string-set! format:en-str format:en-len c)
		    (set! format:en-len (+ format:en-len 1))))))))

       (format:fn-zfill	; fill current number string with 0s
	(lambda (left? n)
	  (if (> (+ n format:fn-len) format:fn-max) ; from the left or right
	      (format:error "number is too long to format (enlarge format:fn-max)"))
	  (set! format:fn-len (+ format:fn-len n))
	  (if left?
	      (do ((i format:fn-len (- i 1)))	; fill n 0s to left
		  ((< i 0))
		(string-set! format:fn-str i
			     (if (< i n)
				 #\0
				 (string-ref format:fn-str (- i n)))))
	      (do ((i (- format:fn-len n) (+ i 1))) ; fill n 0s to the right
		  ((= i format:fn-len))
		(string-set! format:fn-str i #\0)))))

       (format:fn-shiftleft		; shift left current number n positions
	(lambda (n)
	  (if (> n format:fn-len)
	      (format:error "internal error in format:fn-shiftleft (~d,~d)"
			    n format:fn-len))
	  (do ((i n (+ i 1)))
	      ((= i format:fn-len)
	       (set! format:fn-len (- format:fn-len n)))
	    (string-set! format:fn-str (- i n) (string-ref format:fn-str i)))))

       (format:fn-round	; round format:fn-str
	(lambda (digits)
	  (set! digits (+ digits format:fn-dot))
	  (do ((i digits (- i 1))		; "099",2 -> "10"
	       (c 5))				; "023",2 -> "02"
	      ((or (= c 0) (< i 0))		; "999",2 -> "100"
	       (if (= c 1)			; "005",2 -> "01"
		   (begin			; carry overflow
		     (set! format:fn-len digits)
		     (format:fn-zfill #t 1)	; add a 1 before fn-str
		     (string-set! format:fn-str 0 #\1)
		     (set! format:fn-dot (+ format:fn-dot 1)))
		   (set! format:fn-len digits)))
	    (set! c (+ (- (char->integer (string-ref format:fn-str i))
			  format:zero-ch) c))
	    (string-set! format:fn-str i (integer->char
					  (if (< c 10) 
					      (+ c format:zero-ch)
					      (+ (- c 10) format:zero-ch))))
	    (set! c (if (< c 10) 0 1)))))

       (format:fn-out
	(lambda (modifier add-leading-zero?)
	  (if format:fn-pos?
	      (if (eq? modifier 'at) 
		  (format:out-char #\+))
	      (format:out-char #\-))
	  (if (= format:fn-dot 0)
	      (if add-leading-zero?
		  (format:out-char #\0))
	      (format:out-substr format:fn-str 0 format:fn-dot))
	  (format:out-char #\.)
	  (format:out-substr format:fn-str format:fn-dot format:fn-len)))

       (format:en-out
	(lambda (edigits expch)
	  (format:out-char (if expch (integer->char expch) format:expch))
	  (format:out-char (if format:en-pos? #\+ #\-))
	  (if edigits 
	      (if (< format:en-len edigits)
		  (format:out-fill (- edigits format:en-len) #\0)))
	  (format:out-substr format:en-str 0 format:en-len)))

       (format:fn-strip		; strip trailing zeros but one
	(lambda ()
	  (string-set! format:fn-str format:fn-len #\0)
	  (do ((i format:fn-len (- i 1)))
	      ((or (not (char=? (string-ref format:fn-str i) #\0))
		   (<= i format:fn-dot))
	       (set! format:fn-len (+ i 1))))))

       (format:fn-zlead		; count leading zeros
	(lambda ()
	  (do ((i 0 (+ i 1)))
	      ((or (= i format:fn-len)
		   (not (char=? (string-ref format:fn-str i) #\0)))
	       (if (= i format:fn-len)		; found a real zero
		   0
		   i)))))


;;; some global functions not found in SLIB

       (string-capitalize-first	; "hello" -> "Hello"
	(lambda (str)
	  (let ((cap-str (string-copy str))	; "hELLO" -> "Hello"
		(non-first-alpha #f)		; "*hello" -> "*Hello"
		(str-len (string-length str)))	; "hello you" -> "Hello you"
	    (do ((i 0 (+ i 1)))
		((= i str-len) cap-str)
	      (let ((c (string-ref str i)))
		(if (char-alphabetic? c)
		    (if non-first-alpha
			(string-set! cap-str i (char-downcase c))
			(begin
			  (set! non-first-alpha #t)
			  (string-set! cap-str i (char-upcase c))))))))))

       ;; Aborts the program when a formatting error occures. This is a null
       ;; argument closure to jump to the interpreters toplevel continuation.

       (format:abort (lambda () (error "error in format"))))
    
    (set! format:error-save format:error)
    (set! format:fn-str (make-string format:fn-max)) ; number buffer
    (set! format:en-str (make-string format:en-max)) ; exponent buffer
    (apply format:format args)))

;; Thanks to Shuji Narazaki
(module-set! the-root-module 'format format)