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;;; exceptions.scm --- The R6RS exceptions library
;; Copyright (C) 2010 Free Software Foundation, Inc.
;;
;; This library is free software; you can redistribute it and/or
;; modify it under the terms of the GNU Lesser General Public
;; License as published by the Free Software Foundation; either
;; version 3 of the License, or (at your option) any later version.
;;
;; This library 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
;; Lesser General Public License for more details.
;;
;; You should have received a copy of the GNU Lesser General Public
;; License along with this library; if not, write to the Free Software
;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
(library (rnrs exceptions (6))
(export guard with-exception-handler raise raise-continuable)
(import (rnrs base (6))
(rnrs conditions (6))
(rnrs records procedural (6))
(only (guile) with-throw-handler *unspecified* @@))
(define raise (@@ (rnrs records procedural) r6rs-raise))
(define raise-continuable
(@@ (rnrs records procedural) r6rs-raise-continuable))
(define raise-object-wrapper?
(@@ (rnrs records procedural) raise-object-wrapper?))
(define raise-object-wrapper-obj
(@@ (rnrs records procedural) raise-object-wrapper-obj))
(define raise-object-wrapper-continuation
(@@ (rnrs records procedural) raise-object-wrapper-continuation))
(define (with-exception-handler handler thunk)
(with-throw-handler 'r6rs:exception
thunk
(lambda (key . args)
(if (and (not (null? args))
(raise-object-wrapper? (car args)))
(let* ((cargs (car args))
(obj (raise-object-wrapper-obj cargs))
(continuation (raise-object-wrapper-continuation cargs))
(handler-return (handler obj)))
(if continuation
(continuation handler-return)
(raise (make-non-continuable-violation))))
*unspecified*))))
(define-syntax guard0
(syntax-rules ()
((_ (variable cond-clause ...) . body)
(call/cc (lambda (continuation)
(with-exception-handler
(lambda (variable)
(continuation (cond cond-clause ...)))
(lambda () . body)))))))
(define-syntax guard
(syntax-rules (else)
((_ (variable cond-clause ... . ((else else-clause ...))) . body)
(guard0 (variable cond-clause ... (else else-clause ...)) . body))
((_ (variable cond-clause ...) . body)
(guard0 (variable cond-clause ... (else (raise variable))) . body))))
)
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