X-Git-Url: https://git.donarmstrong.com/?a=blobdiff_plain;f=guile18%2Fsrfi%2Fsrfi-34.scm;fp=guile18%2Fsrfi%2Fsrfi-34.scm;h=18a2fda1c545601f2fc043d11fde10a44b84c5ba;hb=139c38d9204dd07f6b235f83bae644faedbc63fd;hp=0000000000000000000000000000000000000000;hpb=652ed35a2013489d0a14fede6307cd2595abb2c4;p=lilypond.git diff --git a/guile18/srfi/srfi-34.scm b/guile18/srfi/srfi-34.scm new file mode 100644 index 0000000000..18a2fda1c5 --- /dev/null +++ b/guile18/srfi/srfi-34.scm @@ -0,0 +1,80 @@ +;;; 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 + +;;; 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 (...) ) +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.