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strott.scm
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1999-02-24
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#| -*-Scheme-*-
$Id: strott.scm,v 14.9 1999/02/24 21:36:25 cph Exp $
Copyright (c) 1988-1999 Massachusetts Institute of Technology
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
|#
;;;; String Output Ports (Truncated)
;;; package: (runtime truncated-string-output)
(declare (usual-integrations))
(define (initialize-package!)
(set! output-string-port-type
(make-port-type `((WRITE-SELF ,operation/write-self)
(WRITE-CHAR ,operation/write-char)
(WRITE-SUBSTRING ,operation/write-substring))
#f)))
(define (with-output-to-truncated-string max thunk)
(call-with-current-continuation
(lambda (return)
(cons #f
(apply string-append
(reverse!
(let ((state
(make-output-string-state return max '() max)))
(with-output-to-port
(make-port output-string-port-type state)
thunk)
(output-string-state/accumulator state))))))))
(define output-string-port-type)
(define-structure (output-string-state (type vector)
(conc-name output-string-state/))
(return #f read-only #t)
(max-length #f read-only #t)
accumulator
counter)
(define (operation/write-char port char)
(let ((state (port/state port)))
(let ((accumulator (output-string-state/accumulator state))
(counter (output-string-state/counter state)))
(if (zero? counter)
((output-string-state/return state)
(cons #t (apply string-append (reverse! accumulator))))
(begin
(set-output-string-state/accumulator!
state
(cons (string char) accumulator))
(set-output-string-state/counter! state (-1+ counter)))))))
(define (operation/write-substring port string start end)
(let ((state (port/state port)))
(let ((accumulator
(cons (substring string start end)
(output-string-state/accumulator state)))
(counter (- (output-string-state/counter state) (- end start))))
(if (negative? counter)
((output-string-state/return state)
(cons #t
(substring (apply string-append (reverse! accumulator))
0
(output-string-state/max-length state))))
(begin
(set-output-string-state/accumulator! state accumulator)
(set-output-string-state/counter! state counter))))))
(define (operation/write-self port output-port)
port
(write-string " to string (truncating)" output-port))