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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) | |
| #:export (with-exception-handler) | |
| #:replace (raise) | |
| #:export-syntax (guard)) | |
| (cond-expand-provide (current-module) '(srfi-34)) | |
| (define throw-key 'srfi-34) | |
| (define (with-exception-handler handler thunk) | |
| "Returns the result(s) of invoking THUNK. HANDLER must be a | |
| procedure that accepts one argument. It is installed as the current | |
| exception handler for the dynamic extent (as determined by | |
| dynamic-wind) of the invocation of THUNK." | |
| (with-throw-handler throw-key | |
| thunk | |
| (lambda (key obj) | |
| (handler obj)))) | |
| (define (raise obj) | |
| "Invokes the current exception handler on OBJ. The handler is | |
| called in the dynamic environment of the call to raise, except that | |
| the current exception handler is that in place for the call to | |
| with-exception-handler that installed the handler being called. The | |
| handler's continuation is otherwise unspecified." | |
| (throw throw-key obj)) | |
| (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* ...) | |
| (catch throw-key | |
| (lambda () body body* ...) | |
| (lambda (key var) | |
| (cond clause ... | |
| (else e e* ...))))) | |
| ((guard (var clause clause* ...) body body* ...) | |
| (catch throw-key | |
| (lambda () body body* ...) | |
| (lambda (key var) | |
| (cond clause clause* ... | |
| (else (throw key var)))))))) | |
| ;;; (srfi srfi-34) ends here. | |