;;; "format.scm" Common LISP text output formatter for SLIB
; Written 1992-1994 by Dirk Lutzebaeck (lutzeb@cs.tu-berlin.de)
;
; 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 the email address above.
; For documentation see slib.texi and format.doc.
; For testing load formatst.scm.
;
; Version 3.0

(provide 'format)
(require 'string-case)
(require 'string-port)
(require 'rev4-optional-procedures)

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

; format string and char output routines on format:port

(define (format:out-str 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))))

(define (format:out-char 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)))

(define (format:out-substr 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)))

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

(define (format:out-fill 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

(define (format:error . args)		; never returns!
  (let ((error-continuation format:error-continuation)
	(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)
    (set! format:error-continuation error-continuation)
    (format:abort)
    (format:intern-error "format:abort does not jump to toplevel!")))

(define format:error-save format:error)

(define (format:intern-error . 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))

(define (format:format . 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"))
  (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)))))
     ((string? destination)		; dest. is format string (Scheme->C)
      (call-with-output-string
       (lambda (port)
	 (format:out port destination arglist))))
     (else
      (format:error "illegal destination `~a'" destination)))))

(define (format:out port fmt args)	; the output handler for a port
  (set! format:port port)		; global port for output routines
  (set! format:case-conversion #f)	; modifier case conversion procedure
  (set! format:flush-output #f)		; ~! reset
  (let ((arg-pos (format:format-work fmt args))
	(arg-len (length args)))
    (cond
     ((< arg-pos arg-len)
      (set! format:arg-pos (+ arg-pos 1))
      (set! format:pos (string-length fmt))
      (format:error "~a superfluous argument~:p" (- arg-len arg-pos)))
     ((> 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))))

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

(define (format:format-work format-string arglist) ; does the formatting work
  (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) slib:tab)
		   (format:out-char slib:tab))
	       (anychar-dispatch))
	      ((#\|)			; Page seperator
	       (if (one-positive-integer? params)
		   (format:out-fill (car params) slib:form-feed)
		   (format:out-char slib:form-feed))
	       (set! format:output-col 0)
	       (anychar-dispatch))
	      ((#\T)			; Tabulate
	       (format:tabulate modifier params)
	       (anychar-dispatch))
	      ((#\Y)			; Pretty-print
	       (require '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"))
		 (else (if (not max-iterations) (set! max-iterations 100))))
	       (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)
				 (>= 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)
				 (>= 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)
				       (>= 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)
				       (>= 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 (eq? modifier 'colon-at)
		   (format:error "double `@' modifier"))
	       (set! modifier (if (eq? modifier 'colon) 'colon-at 'at))
	       (tilde-dispatch))
	      ((#\:)			; `:' modifier
	       (if modifier (format:error "illegal `:' modifier position"))
	       (set! modifier '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 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

;; format:obj->str returns a R4RS representation as a string of an arbitrary
;; scheme object.
;; First parameter is the object, second parameter is a boolean if the
;; representation should be slashified as `write' does.
;; It uses format:char->str which converts a character into
;; a slashified string as `write' does and which is implementation dependent.
;; It uses format:iobj->str to print out internal objects as
;; quoted strings so that the output can always be processed by (read)

(define (format:obj->str obj slashify)
  (cond
   ((string? obj)
    (if slashify
	(let ((obj-len (string-length obj)))
	  (string-append
	   "\""
	   (let loop ((i 0) (j 0))	; taken from Marc Feeley's pp.scm
	     (if (= j obj-len)
		 (string-append (substring obj i j) "\"")
		 (let ((c (string-ref obj j)))
		   (if (or (char=? c #\\)
			   (char=? c #\"))
		       (string-append (substring obj i j) "\\"
				      (loop j (+ j 1)))
		       (loop i (+ j 1))))))))
	obj))
   
   ((boolean? obj) (if obj "#t" "#f"))
   
   ((number? obj) (number->string obj))

   ((symbol? obj) 
    (if format:symbol-case-conv
	(format:symbol-case-conv (symbol->string obj))
	(symbol->string obj)))
   
   ((char? obj)
    (if slashify
	(format:char->str obj)
	(string obj)))
   
   ((null? obj) "()")

   ((input-port? obj)
    (format:iobj->str obj))
   
   ((output-port? obj)
    (format:iobj->str obj))
     
   ((list? obj)
    (string-append "("
		   (let loop ((obj-list obj))
		     (if (null? (cdr obj-list))
			 (format:obj->str (car obj-list) #t)
			 (string-append
			  (format:obj->str (car obj-list) #t)
			  " "
			  (loop (cdr obj-list)))))
		   ")"))

   ((pair? obj)
    (string-append "("
		   (format:obj->str (car obj) #t)
		   " . "
		   (format:obj->str (cdr obj) #t)
		   ")"))
   
   ((vector? obj)
    (string-append "#" (format:obj->str (vector->list obj) #t)))

   (else				; only objects with an #<...> 
    (format:iobj->str obj))))		; representation should fall in here

;; format:iobj->str reveals the implementation dependent representation of 
;; #<...> objects with the use of display and call-with-output-string.
;; If format:read-proof is set to #t the resulting string is additionally 
;; set into string quotes.

(define format:read-proof #f)

(define (format:iobj->str iobj)
  (if (or format:read-proof
	  format:iobj-case-conv)
      (string-append 
       (if format:read-proof "\"" "")
       (if format:iobj-case-conv
	   (format:iobj-case-conv
	    (call-with-output-string (lambda (p) (display iobj p))))
	   (call-with-output-string (lambda (p) (display iobj p))))
       (if format:read-proof "\"" ""))
      (call-with-output-string (lambda (p) (display iobj p)))))


;; 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.

(define (format:char->str 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))))))

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

(define (format:par 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))

(define (format:out-obj-padded 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))))))

(define (format:out-num-padded 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)))))))

(define (format:tabulate 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).

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

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

(define 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"))))

(define 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)

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

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

(define 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))))))))))

(define 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"))

(define 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))))))))))

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

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

(define 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 fixed flonums (~F)

(define (format:out-fixed 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)))

    (if digits

	(begin				; fixed precision
	  (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)))

	(begin				; free precision
	  (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)

(define (format:out-expon 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)))
	 
    (if 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))))

	(begin				; free precision
	  (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)

(define (format:out-general 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)))
    (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 (~$)

(define (format:out-dollar 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)))

    (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

(define format:fn-max 200)		; max. number of number digits
(define format:fn-str (make-string format:fn-max)) ; number buffer
(define format:fn-len 0)		; digit length of number
(define format:fn-dot #f)		; dot position of number
(define format:fn-pos? #t)		; number positive?
(define format:en-max 10)		; max. number of exponent digits
(define format:en-str (make-string format:en-max)) ; exponent buffer
(define format:en-len 0)		; digit length of exponent
(define format:en-pos? #t)		; exponent positive?

(define (format:parse-float 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! left-zeros 0)
		       (set! format:fn-dot (- format:fn-dot left-zeros)))
		     (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)))))

(define (format:en-int)			; 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))))))

(define (format:en-set en)		; set exponent string number
  (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)))))))

(define (format:fn-zfill left? n)	; fill current number string with 0s
  (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))))

(define (format:fn-shiftleft n)		; shift left current number n positions
  (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))))

(define (format:fn-round digits)	; round format:fn-str
  (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))))

(define (format:fn-out 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))

(define (format:en-out 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))

(define (format:fn-strip)		; strip trailing zeros but one
  (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)))))

(define (format:fn-zlead)		; count leading zeros
  (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-index finds the index of the first occurence of the character `c'
;; in the string `s'; it returns #f if there is no such character in `s'.

(define (string-index s c)
  (let ((slen-1 (- (string-length s) 1)))
    (let loop ((i 0))
      (cond
       ((char=? c (string-ref s i)) i)
       ((= i slen-1) #f)
       (else (loop (+ i 1)))))))

(define (string-capitalize-first str)	; "hello" -> "Hello"
  (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)))))))))

(define (list-head l k)
  (if (= k 0)
      '()
      (cons (car l) (list-head (cdr l) (- k 1)))))


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

(define format:abort (lambda () (slib:error "error in format")))

(define format format:format)

;; If this is not possible then a continuation is used to recover
;; properly from a format error. In this case format returns #f.

;(define format:abort
;  (lambda () (format:error-continuation #f)))

;(define format
;  (lambda args				; wraps format:format with an error
;    (call-with-current-continuation	; continuation
;     (lambda (cont)
;       (set! format:error-continuation cont)
;       (apply format:format args)))))

;eof
