scheme-srfi/srfi/28.sld

;; Copyright (C) Scott G. Miller (2002). All Rights Reserved.

;; Made an R7RS library by Taylan Ulrich Bayırlı/Kammer, Copyright (C) 2014.

;; 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.

(define-library (srfi 28)
  (export format)
  (import
   (scheme base)
   (scheme write))
  (begin
    (define format
      (lambda (format-string . objects)
        (let ((buffer (open-output-string)))
          (let loop ((format-list (string->list format-string))
                     (objects objects))
            (cond ((null? format-list) (get-output-string buffer))
                  ((char=? (car format-list) #\~)
                   (if (null? (cdr format-list))
                       (error 'format "Incomplete escape sequence")
                       (case (cadr format-list)
                         ((#\a)
                          (if (null? objects)
                              (error 'format "No value for escape sequence")
                              (begin
                                (display (car objects) buffer)
                                (loop (cddr format-list) (cdr objects)))))
                         ((#\s)
                          (if (null? objects)
                              (error 'format "No value for escape sequence")
                              (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
                          (error 'format "Unrecognized escape sequence")))))
                  (else (write-char (car format-list) buffer)
                        (loop (cdr format-list) objects)))))))))