module/rnrs/exceptions.scm

   1 ;;; exceptions.scm --- The R6RS exceptions library
   2
   3 ;;      Copyright (C) 2010 Free Software Foundation, Inc.
   4 ;;
   5 ;; This library is free software; you can redistribute it and/or
   6 ;; modify it under the terms of the GNU Lesser General Public
   7 ;; License as published by the Free Software Foundation; either
   8 ;; version 3 of the License, or (at your option) any later version.
   9 ;;
  10 ;; This library is distributed in the hope that it will be useful,
  11 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 ;; Lesser General Public License for more details.
  14 ;;
  15 ;; You should have received a copy of the GNU Lesser General Public
  16 ;; License along with this library; if not, write to the Free Software
  17 ;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  18 \f
  19
  20 (library (rnrs exceptions (6))
  21   (export guard with-exception-handler raise raise-continuable)
  22   (import (rnrs base (6))
  23           (rnrs conditions (6))
  24           (rnrs records procedural (6))
  25           (only (guile) with-throw-handler *unspecified* @@))
  26
  27   (define raise (@@ (rnrs records procedural) r6rs-raise))
  28   (define raise-continuable
  29     (@@ (rnrs records procedural) r6rs-raise-continuable))
  30   (define raise-object-wrapper?
  31     (@@ (rnrs records procedural) raise-object-wrapper?))
  32   (define raise-object-wrapper-obj
  33     (@@ (rnrs records procedural) raise-object-wrapper-obj))
  34   (define raise-object-wrapper-continuation
  35     (@@ (rnrs records procedural) raise-object-wrapper-continuation))
  36
  37   (define (with-exception-handler handler thunk)
  38     (with-throw-handler 'r6rs:exception
  39      thunk
  40      (lambda (key . args)
  41        (if (and (not (null? args))
  42                 (raise-object-wrapper? (car args)))
  43            (let* ((cargs (car args))
  44                   (obj (raise-object-wrapper-obj cargs))
  45                   (continuation (raise-object-wrapper-continuation cargs))
  46                   (handler-return (handler obj)))
  47              (if continuation
  48                  (continuation handler-return)
  49                  (raise (make-non-continuable-violation))))
  50            *unspecified*))))
  51
  52   (define-syntax guard0
  53     (syntax-rules ()
  54       ((_ (variable cond-clause ...) . body)
  55        (call/cc (lambda (continuation)
  56                   (with-exception-handler
  57                    (lambda (variable)
  58                      (continuation (cond cond-clause ...)))
  59                    (lambda () . body)))))))
  60
  61   (define-syntax guard
  62     (syntax-rules (else)
  63       ((_ (variable cond-clause ... . ((else else-clause ...))) . body)
  64        (guard0 (variable cond-clause ... (else else-clause ...)) . body))
  65       ((_ (variable cond-clause ...) . body)
  66        (guard0 (variable cond-clause ... (else (raise variable))) . body))))
  67 )