From: "Pascal J. Bourguignon" <pjb@informatimago.com>
To: help-gnu-emacs@gnu.org
Subject: Re: Declaring a local dynamic variable?
Date: Fri, 27 Sep 2013 22:18:24 +0200 [thread overview]
Message-ID: <87zjqyyq5r.fsf@informatimago.com> (raw)
In-Reply-To: mailman.3016.1380307597.10748.help-gnu-emacs@gnu.org
Andreas Röhler <andreas.roehler@easy-emacs.de> writes:
> Let's memorize Stefan's remark as a starting-point to work-on:
>
> " But if d1 and d2 are in two separate packages that know
> nothing about each other but who happen to call each other through some
> potentially twisted sequence of calls, they will still interfere,
> because there's only (globally) one dynamic variable by that name."
>
> Would like to see such a twisted sequence and what makes it's different from a common bug.
With (setq lexical-binding nil).
Here is a case where it's a common bug:
;; --------
(defun p1-f ()
(let ((print-circle t))
(p2-g (function p1-h) '#1=(1 2 . #1#))))
(defun p1-h (data f)
(print data)
(funcall f))
;; --------
(defun p2-g (p d)
(let ((print-circle nil))
(funcall p '(1 2 3) (function p2-i))))
(defun p2-i (data)
(print data))
;; --------
Here is a case where it's not a common bug:
;; --------
(defun p1-f ()
(let ((be-careful t))
(p2-g (function p1-h) '#1=(1 2 . #1#))))
(defun p1-h (data f)
(if be-careful
(let ((print-circle t)) (print data))
(print data))
(funcall f))
;; --------
(defun p2-g (p d)
(let ((be-careful nil))
(funcall p '(1 2 3) (function p2-i))))
(defun p2-i (data)
(if be-careful
(let ((print-circle t)) (print data))
(print data)))
;; --------
The difference is that in the first case, there's a global definition
for print-circle, while in the second case, the packages expect
be-careful to be local special variables. You could use my macros and
(declare (special be-careful)) in each package, and the bug would
persist.
However, it would NOT occur in Common Lisp, where you'd have (in-package
"P1") and (in-package "P2") forms in front of each bodies of code,
because you'd have actually TWO special symbols: p1::be-careful and
p2::be-careful.
The conclusion is that in emacs lisp you have to prefix ALL the symbols!
Which clearly demonstrates a failure of the language.
--
__Pascal Bourguignon__
http://www.informatimago.com/
next prev parent reply other threads:[~2013-09-27 20:18 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-20 9:52 Declaring a local dynamic variable? Joost Kremers
2013-09-20 12:30 ` Stefan Monnier
2013-09-20 14:54 ` Andreas Röhler
[not found] ` <mailman.2569.1379688787.10748.help-gnu-emacs@gnu.org>
2013-09-20 15:10 ` Barry Margolin
2013-09-20 16:34 ` Andreas Röhler
[not found] ` <mailman.2578.1379694764.10748.help-gnu-emacs@gnu.org>
2013-09-20 20:59 ` Barry Margolin
2013-09-21 5:49 ` Andreas Röhler
2013-09-23 16:19 ` Joost Kremers
[not found] ` <mailman.2622.1379742443.10748.help-gnu-emacs@gnu.org>
2013-09-21 11:31 ` Barry Margolin
2013-09-21 13:32 ` Andreas Röhler
[not found] ` <mailman.2638.1379770251.10748.help-gnu-emacs@gnu.org>
2013-09-22 3:49 ` Barry Margolin
2013-09-23 16:26 ` Joost Kremers
2013-09-23 21:17 ` Barry Margolin
2013-09-23 22:14 ` Joost Kremers
2013-09-24 0:03 ` Barry Margolin
2013-09-25 8:58 ` Joost Kremers
2013-09-22 17:11 ` Pascal J. Bourguignon
2013-09-23 16:17 ` Joost Kremers
2013-09-24 21:40 ` Stefan Monnier
2013-11-02 23:56 ` WJ
2013-11-03 1:42 ` WJ
[not found] ` <mailman.2566.1379680283.10748.help-gnu-emacs@gnu.org>
2013-09-23 16:11 ` Joost Kremers
2013-09-24 21:34 ` Stefan Monnier
2013-09-25 5:52 ` Andreas Röhler
2013-09-25 7:24 ` Stefan Monnier
2013-09-25 8:43 ` Joost Kremers
2013-09-25 12:26 ` Stefan Monnier
2013-10-12 16:54 ` Andreas Röhler
[not found] ` <mailman.3886.1381596756.10748.help-gnu-emacs@gnu.org>
2013-10-12 21:25 ` Kai Grossjohann
2013-10-13 8:12 ` Andreas Röhler
2013-10-13 13:37 ` Stefan Monnier
2013-10-13 17:41 ` Andreas Röhler
2013-10-13 19:56 ` Kai Großjohann
[not found] ` <mailman.2843.1380112007.10748.help-gnu-emacs@gnu.org>
2013-09-25 15:46 ` Barry Margolin
2013-09-25 18:53 ` Stefan Monnier
2013-09-27 9:53 ` Andreas Röhler
2013-09-27 13:15 ` Stefan Monnier
[not found] ` <mailman.2982.1380275511.10748.help-gnu-emacs@gnu.org>
2013-09-27 14:31 ` Barry Margolin
2013-09-27 18:48 ` Andreas Röhler
[not found] ` <mailman.3016.1380307597.10748.help-gnu-emacs@gnu.org>
2013-09-27 20:18 ` Pascal J. Bourguignon [this message]
2013-09-27 23:57 ` Stefan Monnier
2013-09-28 6:20 ` Andreas Röhler
2013-09-28 6:24 ` W. Greenhouse
2013-09-28 6:50 ` Andreas Röhler
2013-09-28 7:21 ` W. Greenhouse
[not found] ` <mailman.2873.1380135245.10748.help-gnu-emacs@gnu.org>
2013-09-26 0:06 ` Barry Margolin
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