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- ;;; srfi-34.scm --- Exception handling for programs
- ;; Copyright (C) 2003, 2006, 2008, 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
- ;;; Author: Neil Jerram <neil@ossau.uklinux.net>
- ;;; Commentary:
- ;; This is an implementation of SRFI-34: Exception Handling for
- ;; Programs. For documentation please see the SRFI-34 document; this
- ;; module is not yet documented at all in the Guile manual.
- ;;; Code:
- (define-module (srfi srfi-34)
- #:re-export (with-exception-handler
- (raise-exception . raise))
- #:export-syntax (guard))
- (cond-expand-provide (current-module) '(srfi-34))
- (define-syntax guard
- (syntax-rules (else)
- "Syntax: (guard (<var> <clause1> <clause2> ...) <body>)
- Each <clause> should have the same form as a `cond' clause.
- Semantics: Evaluating a guard form evaluates <body> with an exception
- handler that binds the raised object to <var> and within the scope of
- that binding evaluates the clauses as if they were the clauses of a
- cond expression. That implicit cond expression is evaluated with the
- continuation and dynamic environment of the guard expression. If
- every <clause>'s <test> evaluates to false and there is no else
- clause, then raise is re-invoked on the raised object within the
- dynamic environment of the original call to raise except that the
- current exception handler is that of the guard expression."
- ((guard (var clause ... (else e e* ...)) body body* ...)
- (with-exception-handler
- (lambda (var)
- (cond clause ...
- (else e e* ...)))
- (lambda () body body* ...)
- #:unwind? #t))
- ((guard (var clause clause* ...) body body* ...)
- (let ((tag (make-prompt-tag)))
- (call-with-prompt
- tag
- (lambda ()
- (with-exception-handler
- (lambda (exn)
- (abort-to-prompt tag exn)
- (raise-exception exn))
- (lambda () body body* ...)))
- (lambda (rewind var)
- (cond clause clause* ...
- (else (rewind)))))))))
- ;;; (srfi srfi-34) ends here.
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