From: Barry Margolin <barmar@alum.mit.edu>
To: help-gnu-emacs@gnu.org
Subject: Re: DynamicBindingVsLexicalBinding
Date: Wed, 16 Oct 2013 10:26:54 -0400 [thread overview]
Message-ID: <barmar-AF232A.10265416102013@news.eternal-september.org> (raw)
In-Reply-To: mailman.4127.1381928277.10748.help-gnu-emacs@gnu.org
In article <mailman.4127.1381928277.10748.help-gnu-emacs@gnu.org>,
phillip.lord@newcastle.ac.uk (Phillip Lord) wrote:
> Perhaps my understanding is not complete, but I always thought that
> dynamic and static binding was about variables that are unbound. If we
> have global variables with mutable state, then as far as I can see, you
> could do something equivalent with either.
>
> So, this...
>
> (defun perldoc ()
> (interactive)
> (require 'man)
> (let ((manual-program "perldoc"))
> (call-interactively 'man)))
>
> is nearly equivalent to
>
> (defun perldoc()
> (interactive)
> (require 'man)
> (let ((old manual-program))
> (setq manual-program "perldoc")
> (call-interactively 'man)
> (setq manual-program old))
>
>
> If we were multi-threaded, then AFAICT, the let version would be
> cleaner -- as the altered manual-program is *only* in the dynamic
> environment of the call to the perldoc command. So another call to the
> man function would be unaffected. While the second changes global state,
> and then changes it back. But, we aren't.
You also need unwind-protect to ensure that the value is reverted if the
code aborts.
With that fix, it's essentially how most implementations of dynamic
binding worked in single-threaded Lisps. But multi-threaded Lisps need
to add hooks into thread switching.
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
next prev parent reply other threads:[~2013-10-16 14:26 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-12 17:56 DynamicBindingVsLexicalBinding Andreas Röhler
2013-10-12 18:35 ` DynamicBindingVsLexicalBinding Dmitry Gutov
2013-10-12 20:53 ` DynamicBindingVsLexicalBinding Drew Adams
2013-10-13 5:09 ` DynamicBindingVsLexicalBinding Thien-Thi Nguyen
2013-10-13 7:54 ` DynamicBindingVsLexicalBinding Andreas Röhler
2013-10-13 13:46 ` DynamicBindingVsLexicalBinding Kai Großjohann
2013-10-13 16:21 ` DynamicBindingVsLexicalBinding Drew Adams
2013-10-14 11:21 ` DynamicBindingVsLexicalBinding Phillip Lord
2013-10-14 13:45 ` DynamicBindingVsLexicalBinding Drew Adams
2013-10-14 16:05 ` DynamicBindingVsLexicalBinding Phillip Lord
2013-10-14 21:32 ` DynamicBindingVsLexicalBinding Kai Großjohann
2013-10-15 11:27 ` DynamicBindingVsLexicalBinding Phillip Lord
2013-10-15 20:43 ` DynamicBindingVsLexicalBinding Kai Großjohann
2013-10-16 12:57 ` DynamicBindingVsLexicalBinding Phillip Lord
[not found] ` <mailman.4127.1381928277.10748.help-gnu-emacs@gnu.org>
2013-10-16 14:26 ` Barry Margolin [this message]
[not found] ` <mailman.3929.1381681317.10748.help-gnu-emacs@gnu.org>
2013-10-14 11:27 ` DynamicBindingVsLexicalBinding Rustom Mody
2013-10-14 11:15 ` DynamicBindingVsLexicalBinding Phillip Lord
[not found] <mailman.3891.1381600459.10748.help-gnu-emacs@gnu.org>
2013-10-13 3:34 ` DynamicBindingVsLexicalBinding Barry Margolin
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