From: Sebastian Wiesner <swiesner@lunaryorn.com>
To: help-gnu-emacs@gnu.org
Cc: Emanuel Berg <embe8573@student.uu.se>
Subject: Re: run-with-timer does not display message
Date: Sun, 20 Jul 2014 14:15:19 +0200 [thread overview]
Message-ID: <2499282.TBjfJc2tWs@lunaryorn-fedora> (raw)
In-Reply-To: <878unputvv.fsf@debian.uxu>
Am Samstag, 19. Juli 2014, 19:43:16 schrieb Emanuel Berg:
> 2. Interestingly, what I can see, my method, with
> backticks and commas, isn't that "lexical" - because
> then, there, the actual values are inserted?
Note quite. The backquote is “static” in that it captures the *value* of the
variable at the time the backquote is evaluated. “Lexical” binding captures
the *variable itself*.
This makes a difference if the variable is changed after capturing.
Considering the following example:
ELISP> (let ((i 10))
(setq f-lexical (lambda () i))
(setq f-backquote `(lambda () ,i))
(setq i 20))
20 (#o24, #x14, ?\C-t)
ELISP> (funcall f-lexical)
20 (#o24, #x14, ?\C-t)
ELISP> (funcall f-backquote)
10 (#o12, #xa, ?\C-j)
As you can see, changing "i" *after* creating the functions only affects the
closure created by lexical binding. The function created by the backquote is
left untouched.
This specific behaviour is what makes lexical binding special: Capturing
*lexical variables* in closures, as opposed to capturing values (by
backquotes) or just using dynamic variables. You cannot easily and
efficiently emulated this behaviour with macros and backquotes.
next prev parent reply other threads:[~2014-07-20 12:15 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-15 13:47 run-with-timer does not display message Matthias Pfeifer
2014-07-15 13:53 ` Thorsten Jolitz
2014-07-18 16:26 ` Stefan Monnier
[not found] ` <mailman.5631.1405701027.1147.help-gnu-emacs@gnu.org>
2014-07-18 21:34 ` Emanuel Berg
2014-07-19 15:09 ` Sebastian Wiesner
2014-07-19 15:27 ` Eli Zaretskii
2014-07-19 17:08 ` Stefan Monnier
2014-07-19 18:04 ` Drew Adams
[not found] ` <mailman.5702.1405789759.1147.help-gnu-emacs@gnu.org>
2014-07-19 17:43 ` Emanuel Berg
2014-07-19 18:12 ` Stefan Monnier
2014-07-19 20:06 ` Lexical and Dynamic Scope Robert Thorpe
2014-07-20 12:15 ` Sebastian Wiesner [this message]
2014-07-21 13:26 ` run-with-timer does not display message Stefan Monnier
[not found] ` <mailman.5708.1405793578.1147.help-gnu-emacs@gnu.org>
2014-07-20 19:27 ` Emanuel Berg
2014-07-21 13:29 ` Stefan Monnier
[not found] ` <mailman.5813.1405950328.1147.help-gnu-emacs@gnu.org>
2014-07-21 22:17 ` Emanuel Berg
2014-07-24 8:25 ` Stefan Monnier
[not found] ` <mailman.5754.1405858540.1147.help-gnu-emacs@gnu.org>
2014-07-20 19:37 ` Emanuel Berg
2014-07-20 20:11 ` Drew Adams
2014-07-20 21:28 ` dynamic and lexical scope, attempted summary with example (was: Re: run-with-timer does not display message) Emanuel Berg
2014-07-21 4:44 ` dynamic and lexical scope, attempted summary with example Thien-Thi Nguyen
2014-07-21 6:36 ` Thorsten Jolitz
[not found] ` <mailman.5796.1405924598.1147.help-gnu-emacs@gnu.org>
2014-07-21 14:08 ` Emanuel Berg
2014-07-21 9:23 ` Michael Heerdegen
[not found] ` <mailman.5792.1405917701.1147.help-gnu-emacs@gnu.org>
2014-07-21 13:36 ` Emanuel Berg
2014-07-21 17:07 ` Thien-Thi Nguyen
[not found] ` <mailman.5826.1405962249.1147.help-gnu-emacs@gnu.org>
2014-07-21 22:11 ` Emanuel Berg
[not found] ` <mailman.5805.1405934637.1147.help-gnu-emacs@gnu.org>
2014-07-21 14:02 ` Emanuel Berg
[not found] ` <mailman.5686.1405782584.1147.help-gnu-emacs@gnu.org>
2014-07-19 17:49 ` run-with-timer does not display message Emanuel Berg
[not found] ` <mailman.5455.1405432451.1147.help-gnu-emacs@gnu.org>
2014-07-15 15:35 ` Emanuel Berg
[not found] <mailman.5454.1405432029.1147.help-gnu-emacs@gnu.org>
2014-07-15 14:34 ` Joost Kremers
2014-07-15 15:18 ` jduthen
2014-07-15 15:20 ` Joost Kremers
2014-07-15 15:40 ` Drew Adams
[not found] ` <mailman.5461.1405438875.1147.help-gnu-emacs@gnu.org>
2014-07-15 15:52 ` Joost Kremers
2014-07-15 15:57 ` Emanuel Berg
[not found] ` <mailman.5463.1405440423.1147.help-gnu-emacs@gnu.org>
2014-07-15 16:07 ` Emanuel Berg
2014-07-15 16:12 ` Joost Kremers
[not found] ` <mailman.5466.1405442248.1147.help-gnu-emacs@gnu.org>
2014-07-16 1:12 ` Joost Kremers
2014-07-17 10:03 ` Matthias Pfeifer
[not found] ` <<slrnlsakmh.a5k.joost.m.kremers@j.kremers4.news.arnhem.chello.nl>
2014-07-15 16:37 ` Drew Adams
[not found] ` <<slrnlsaji8.a5k.joost.m.kremers@j.kremers4.news.arnhem.chello.nl>
2014-07-15 16:06 ` Drew Adams
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