lisp/url/url-future.el

   1 ;;; url-future.el --- general futures facility for url.el
   2
   3 ;; Copyright (C) 2011-2012  Free Software Foundation, Inc.
   4
   5 ;; Author: Teodor Zlatanov <tzz@lifelogs.com>
   6 ;; Keywords: data
   7
   8 ;; This file is part of GNU Emacs.
   9 ;;
  10 ;; GNU Emacs is free software: you can redistribute it and/or modify
  11 ;; it under the terms of the GNU General Public License as published by
  12 ;; the Free Software Foundation, either version 3 of the License, or
  13 ;; (at your option) any later version.
  14
  15 ;; GNU Emacs is distributed in the hope that it will be useful,
  16 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 ;; GNU General Public License for more details.
  19
  20 ;; You should have received a copy of the GNU General Public License
  21 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  22
  23 ;;; Commentary:
  24
  25 ;; Make a url-future (basically a defstruct):
  26 ;; (make-url-future :value (lambda () (calculation goes here))
  27 ;;   :callback (lambda (future) (use future on success))
  28 ;;   :errorback (lambda (future &rest error) (error handler)))
  29
  30 ;; Then either call it with `url-future-call' or cancel it with
  31 ;; `url-future-cancel'.  Generally the functions will return the
  32 ;; future itself, not the value it holds.  Also the functions will
  33 ;; throw a url-future-already-done error if you try to call or cancel
  34 ;; a future more than once.
  35
  36 ;; So, to get the value:
  37 ;; (when (url-future-completed-p future) (url-future-value future))
  38
  39 ;; See `url-future-tests' and the code below for further details.
  40
  41 ;;; Code:
  42
  43 (eval-when-compile (require 'cl))
  44
  45 (defstruct url-future callback errorback status value)
  46
  47 (defmacro url-future-done-p (url-future)
  48   `(url-future-status ,url-future))
  49
  50 (defmacro url-future-completed-p (url-future)
  51   `(eq (url-future-status ,url-future) t))
  52
  53 (defmacro url-future-errored-p (url-future)
  54   `(eq (url-future-status ,url-future) 'error))
  55
  56 (defmacro url-future-cancelled-p (url-future)
  57   `(eq (url-future-status ,url-future) 'cancel))
  58
  59 (defun url-future-finish (url-future &optional status)
  60   (if (url-future-done-p url-future)
  61       (signal 'error 'url-future-already-done)
  62     (setf (url-future-status url-future) (or status t))
  63     ;; the status must be such that the future was completed
  64     ;; to run the callback
  65     (when (url-future-completed-p url-future)
  66       (funcall (or (url-future-callback url-future) 'ignore)
  67                url-future))
  68     url-future))
  69
  70 (defun url-future-errored (url-future errorcons)
  71   (if (url-future-done-p url-future)
  72       (signal 'error 'url-future-already-done)
  73     (setf (url-future-status url-future) 'error)
  74     (setf (url-future-value url-future) errorcons)
  75     (funcall (or (url-future-errorback url-future) 'ignore)
  76              url-future errorcons)))
  77
  78 (defun url-future-call (url-future)
  79   (if (url-future-done-p url-future)
  80       (signal 'error 'url-future-already-done)
  81     (let ((ff (url-future-value url-future)))
  82       (when (functionp ff)
  83         (condition-case catcher
  84             (setf (url-future-value url-future)
  85                   (funcall ff))
  86           (error (url-future-errored url-future catcher)))
  87         (url-future-value url-future)))
  88     (if (url-future-errored-p url-future)
  89         url-future
  90       (url-future-finish url-future))))
  91
  92 (defun url-future-cancel (url-future)
  93   (if (url-future-done-p url-future)
  94       (signal 'error 'url-future-already-done)
  95     (url-future-finish url-future 'cancel)))
  96
  97 (provide 'url-future)
  98 ;;; url-future.el ends here