| 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081 |
- ;;; srfi-34.scm --- Exception handling for programs
- ;; Copyright (C) 2003, 2006, 2008 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 2.1 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
- 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-macro (guard var+clauses . body)
- "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."
- (let ((var (car var+clauses))
- (clauses (cdr var+clauses)))
- `(catch ',throw-key
- (lambda ()
- ,@body)
- (lambda (key ,var)
- (cond ,@(if (eq? (caar (last-pair clauses)) 'else)
- clauses
- (append clauses
- `((else (throw key ,var))))))))))
- ;;; (srfi srfi-34) ends here.
|
