scheme48/scheme/srfi/srfi-28.scm

; Copyright (C) Scott G. Miller (2002). All Rights Reserved.
; 
; Permission is hereby granted, free of charge, to any person
; obtaining a copy of this software and associated documentation files
; (the "Software"), to deal in the Software without restriction,
; including without limitation the rights to use, copy, modify, merge,
; publish, distribute, sublicense, and/or sell copies of the Software,
; and to permit persons to whom the Software is furnished to do so,
; subject to the following conditions:
; 
; The above copyright notice and this permission notice shall be
; included in all copies or substantial portions of the Software.
; 
; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
; MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
; NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
; BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
; ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
; CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
; SOFTWARE.

;; Revised uses of ERROR as compared to the reference implementation.

(define format
  (lambda (format-string . the-objects)
    (let ((buffer (open-output-string)))
      (let loop ((format-list (string->list format-string))
                 (objects the-objects))
        (cond ((null? format-list) (get-output-string buffer))
              ((char=? (car format-list) #\~)
               (if (null? (cdr format-list))
                   (assertion-violation 'format "Incomplete escape sequence" format-string)
                   (case (cadr format-list)
                     ((#\a)
                      (if (null? objects)
                          (apply assertion-violation 'format "No value for escape sequence"
				 format-string the-objects)
                          (begin
                            (display (car objects) buffer)
                            (loop (cddr format-list) (cdr objects)))))
	             ((#\s)
                      (if (null? objects)
                          (apply assertion-violation 'format "No value for escape sequence"
				 format-string the-objects)
                          (begin
                            (write (car objects) buffer)
                            (loop (cddr format-list) (cdr objects)))))
                     ((#\%)
                      (newline buffer)
                      (loop (cddr format-list) objects))
                     ((#\~)
                      (write-char #\~ buffer)
                      (loop (cddr format-list) objects))
                     (else
                      (assertion-violation 'format "Unrecognized escape sequence" format-string)))))
              (else (write-char (car format-list) buffer)
                    (loop (cdr format-list) objects)))))))