From 0f443a12368d02e256c7e94c3de574c6ceaed86e Mon Sep 17 00:00:00 2001 From: Nicolas Petton Date: Fri, 23 Oct 2015 13:20:45 +0200 Subject: New library thunk.el thunk.el is extracted from stream.el in ELPA, with additional tests. * lisp/emacs-lisp/thunk.el: New file. * test/automated/thunk-tests.el: New file. * etc/NEWS: Add information about thunk.el --- lisp/emacs-lisp/thunk.el | 63 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 63 insertions(+) create mode 100644 lisp/emacs-lisp/thunk.el (limited to 'lisp/emacs-lisp') diff --git a/lisp/emacs-lisp/thunk.el b/lisp/emacs-lisp/thunk.el new file mode 100644 index 00000000000..ab366d295f5 --- /dev/null +++ b/lisp/emacs-lisp/thunk.el @@ -0,0 +1,63 @@ +;;; thunk.el --- Lazy form evaluation -*- lexical-binding: t -*- + +;; Copyright (C) 2015 Free Software Foundation, Inc. + +;; Author: Nicolas Petton +;; Keywords: sequences +;; Version: 1.0 +;; Package: thunk + +;; Maintainer: emacs-devel@gnu.org + +;; This file is part of GNU Emacs. + +;; GNU Emacs is free software: you can redistribute it and/or modify +;; it under the terms of the GNU General Public License as published by +;; the Free Software Foundation, either version 3 of the License, or +;; (at your option) any later version. + +;; GNU Emacs 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 General Public License for more details. + +;; You should have received a copy of the GNU General Public License +;; along with GNU Emacs. If not, see . + +;;; Commentary: +;; +;; Thunk provides functions and macros to control the evaluation of +;; forms. Use `thunk-delay' to delay the evaluation of a form, and +;; `thunk-force' to evaluate it. Evaluation is cached, and only +;; happens once. + +;; Tests are located at test/automated/thunk-tests.el + +;;; Code: + +(defmacro thunk-delay (&rest body) + "Delay the evaluation of BODY." + (declare (debug t)) + (let ((forced (make-symbol "forced")) + (val (make-symbol "val"))) + `(let (,forced ,val) + (lambda (&optional check) + (if check + ,forced + (unless ,forced + (setf ,val (progn ,@body)) + (setf ,forced t))) + ,val)))) + +(defun thunk-force (delayed) + "Force the evaluation of DELAYED. +The result is cached and will be returned on subsequent calls +with the same DELAYED argument." + (funcall delayed)) + +(defun thunk-evaluated-p (delayed) + "Return non-nil if DELAYED has been evaluated." + (funcall delayed t)) + +(provide 'thunk) +;;; thunk.el ends here -- cgit v1.2.3