* url-future.el: Add general futures facility.

2 files changed, 130 insertions, 0 deletions

diff --git a/lisp/url/ChangeLog b/lisp/url/ChangeLog
index 37a9fb8ffe..910234eca1 100644
--- a/lisp/url/ChangeLog
+++ b/lisp/url/ChangeLog
@@ -1,3 +1,7 @@
+2011-05-31  Teodor Zlatanov  <[email protected]>
+
+	* url-future.el: Add general futures facility.
+
 2011-05-29  Leo Liu  <[email protected]>
 
 	* url-cookie.el (url-cookie): Add option :named so that
diff --git a/lisp/url/url-future.el b/lisp/url/url-future.el
new file mode 100644
index 0000000000..334c4fa912
--- /dev/null
+++ b/lisp/url/url-future.el
@@ -0,0 +1,126 @@
+;;; url-future.el --- general futures facility for url.el
+
+;; Copyright (C) 2011  Free Software Foundation, Inc.
+
+;; Author: Teodor Zlatanov <[email protected]>
+;; 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 <http://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 the ERT tests and the code for futher details.
+
+;;; Code:
+
+(eval-when-compile (require 'cl))
+(eval-when-compile (require 'ert))
+
+(defstruct url-future callback errorback status value)
+
+(defmacro url-future-done-p (url-future)
+  `(url-future-status ,url-future))
+
+(defmacro url-future-completed-p (url-future)
+  `(eq (url-future-status ,url-future) t))
+
+(defmacro url-future-errored-p (url-future)
+  `(eq (url-future-status ,url-future) 'error))
+
+(defmacro url-future-cancelled-p (url-future)
+  `(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)))
+        (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)))
+
+(ert-deftest url-future-test ()
+  (let* ((text "running future")
+         (good (make-url-future :value (lambda () (format text))
+                                :callback (lambda (f) (set 'saver f))))
+         (bad (make-url-future :value (lambda () (/ 1 0))
+                               :errorback (lambda (&rest d) (set 'saver d))))
+         (tocancel (make-url-future :value (lambda () (/ 1 0))
+                                    :callback (lambda (f) (set 'saver f))
+                                    :errorback (lambda (&rest d)
+                                                 (set 'saver d))))
+         saver)
+    (should (equal good (url-future-call good)))
+    (should (equal good saver))
+    (should (equal text (url-future-value good)))
+    (should (url-future-completed-p good))
+    (should-error (url-future-call good))
+    (setq saver nil)
+    (should (equal bad (url-future-call bad)))
+    (should-error (url-future-call bad))
+    (should (equal saver (list bad '(arith-error))))
+    (should (url-future-errored-p bad))
+    (setq saver nil)
+    (should (equal (url-future-cancel tocancel) tocancel))
+    (should-error (url-future-call tocancel))
+    (should (null saver))
+    (should (url-future-cancelled-p tocancel))))
+
+(provide 'url-future)
+;;; url-future.el ends here