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;;; url-future.el --- general futures facility for url.el -*- lexical-binding: t -*-
;; Copyright (C) 2011-2019 Free Software Foundation, Inc.
;; Author: Teodor Zlatanov <tzz@lifelogs.com>
;; Keywords: data
;; 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:
;; Make a url-future (basically a defstruct):
;; (make-url-future :value (lambda () (calculation goes here))
;; :callback (lambda (future) (use future on success))
;; :errorback (lambda (future &rest error) (error handler)))
;; Then either call it with `url-future-call' or cancel it with
;; `url-future-cancel'. Generally the functions will return the
;; future itself, not the value it holds. Also the functions will
;; throw a url-future-already-done error if you try to call or cancel
;; a future more than once.
;; So, to get the value:
;; (when (url-future-completed-p future) (url-future-value future))
;; See `url-future-tests' and the code below for further details.
;;; Code:
(eval-when-compile (require 'cl-lib))
(cl-defstruct url-future callback errorback status value)
(define-inline url-future-done-p (url-future)
(inline-quote (url-future-status ,url-future)))
(define-inline url-future-completed-p (url-future)
(inline-quote (eq (url-future-status ,url-future) t)))
(define-inline url-future-errored-p (url-future)
(inline-quote (eq (url-future-status ,url-future) 'error)))
(define-inline url-future-cancelled-p (url-future)
(inline-quote (eq (url-future-status ,url-future) 'cancel)))
(defun url-future-finish (url-future &optional status)
(if (url-future-done-p url-future)
(signal 'error 'url-future-already-done)
(setf (url-future-status url-future) (or status t))
;; the status must be such that the future was completed
;; to run the callback
(when (url-future-completed-p url-future)
(funcall (or (url-future-callback url-future) 'ignore)
url-future))
url-future))
(defun url-future-errored (url-future errorcons)
(if (url-future-done-p url-future)
(signal 'error 'url-future-already-done)
(setf (url-future-status url-future) 'error)
(setf (url-future-value url-future) errorcons)
(funcall (or (url-future-errorback url-future) 'ignore)
url-future errorcons)))
(defun url-future-call (url-future)
(if (url-future-done-p url-future)
(signal 'error 'url-future-already-done)
(let ((ff (url-future-value url-future)))
(when (functionp ff)
(condition-case catcher
(setf (url-future-value url-future)
(funcall ff))
(error (url-future-errored url-future catcher)))
;; Unused return value.
;;; (url-future-value url-future)
))
(if (url-future-errored-p url-future)
url-future
(url-future-finish url-future))))
(defun url-future-cancel (url-future)
(if (url-future-done-p url-future)
(signal 'error 'url-future-already-done)
(url-future-finish url-future 'cancel)))
(provide 'url-future)
;;; url-future.el ends here
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