;;; srfi-34.scm --- Exception handling for programs ;; Copyright (C) 2003 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA ;;; Author: Neil Jerram ;;; 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)) (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." (lazy-catch 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 ( ...) ) Each should have the same form as a `cond' clause. Semantics: Evaluating a guard form evaluates with an exception handler that binds the raised object to 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 's 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.