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blob 0c5d0b709e3d59b261efcfc3589a9af188f38712 2305 bytes (raw)
name: lisp/emacs-lisp/thunk.el 	 # note: path name is non-authoritative(*)

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;;; thunk.el --- Lazy form evaluation  -*- lexical-binding: t -*-

;; Copyright (C) 2015-2017 Free Software Foundation, Inc.

;; Author: Nicolas Petton <nicolas@petton.fr>
;; 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 <https://www.gnu.org/licenses/>.

;;; Commentary:
;;
;; Thunk provides functions and macros to delay the evaluation of
;; forms.
;;
;; Use `thunk-delay' to delay the evaluation of a form (requires
;; lexical-binding), and `thunk-force' to evaluate it. The result of
;; the evaluation is cached, and only happens once.
;;
;; Here is an example of a form which evaluation is delayed:
;;
;;     (setq delayed (thunk-delay (message "this message is delayed")))
;;
;; `delayed' is not evaluated until `thunk-force' is called, like the
;; following:
;;
;;    (thunk-force delayed)

;;; Code:

(eval-when-compile (require 'cl-macs))

;;;###autoload
(defmacro thunk-delay (&rest body)
  "Delay the evaluation of BODY."
  (declare (debug t))
  (cl-assert lexical-binding)
  (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)))))

;;;###autoload
(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

debug log:

solving 0c5d0b709e ...
found 0c5d0b709e in https://yhetil.org/emacs/87o9ocd6s4.fsf@web.de/
found 371d10444b in https://git.savannah.gnu.org/cgit/emacs.git
preparing index
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100644 371d10444b2fb0efaced00a57e0a8a8854596b3f	lisp/emacs-lisp/thunk.el

applying [1/1] https://yhetil.org/emacs/87o9ocd6s4.fsf@web.de/
diff --git a/lisp/emacs-lisp/thunk.el b/lisp/emacs-lisp/thunk.el
index 371d10444b..0c5d0b709e 100644

Checking patch lisp/emacs-lisp/thunk.el...
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skipping https://yhetil.org/emacs/87o9ocd6s4.fsf@web.de/ for 0c5d0b709e
index at:
100644 0c5d0b709e3d59b261efcfc3589a9af188f38712	lisp/emacs-lisp/thunk.el

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