From: "Andreas Röhler" <andreas.roehler@easy-emacs.de>
To: help-gnu-emacs@gnu.org
Subject: Re: Surrounding Lexical Variable Reference in the Body of defun
Date: Wed, 22 Aug 2012 08:42:24 +0200 [thread overview]
Message-ID: <50347F50.4000506@easy-emacs.de> (raw)
In-Reply-To: <8b43586d-2ad4-4cf6-ae15-446e909bf496@googlegroups.com>
Am 21.08.2012 08:07, schrieb Deokhwan Kim:
> Hi there,
>
> I'm having trouble understanding lexical binding in Emacs 24. I came across the following sentence in the Emacs Lisp manual <http://www.gnu.org/software/emacs/manual/html_node/elisp/Lexical-Binding.html>:
>
>> the code in the body of a defun or defmacro cannot refer to surrounding lexical variables.
>
> It was a great shock to me because it sounded quite awkward and Common Lisp does not have such restriction AFAIK. Rather, I suspected that I might misunderstand what the sentence really meant. So I decided to make some experiments with the following code stored in foo.el:
>
> ;;; -*- lexical-binding: t -*-
> (let ((x 0))
> (defun counter ()
> (setq x (1+ x))))
>
> (message "%d" (counter))
> (message "%d" (counter))
>
> Surprisingly, when I ran it in the form of source code, it worked:
>
> $ emacs -Q -batch -l foo.el
> 1
> 2
>
> On the other hand, when I tried to byte-compile it, I got the following warning messages:
>
> $ emacs -Q -batch -f batch-byte-compile foo.el
> In toplevel form:
> foo.el:2:1:Warning: Function counter will ignore its context (x)
> foo.el:2:1:Warning: Unused lexical variable `x'
> foo.el:4:11:Warning: reference to free variable `x'
> foo.el:4:17:Warning: assignment to free variable `x'
>
> In end of data:
> foo.el:8:1:Warning: the function `counter' is not known to be defined.
> Wrote foo.elc
>
> When I ran the resulting byte-compiled code, I got an error as the manual claims:
>
> $ emacs -Q -batch -l foo.elc
> Symbol's value as variable is void: x
>
> Now I'm so confused. Here are my two questions:
>
> 1. Why does this restriction exists? Is it inevitable because of some design decision of Emacs? Or is it temporary and removed in a (near) future release?
> 2. Why does the original source code behave differently from its compiled code?
>
> Best regards,
> Deokhwan Kim
>
as this question isn't raised first time, maybe Emacs developers consider to revert that change?
next prev parent reply other threads:[~2012-08-22 6:42 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-21 6:07 Surrounding Lexical Variable Reference in the Body of defun Deokhwan Kim
2012-08-22 6:42 ` Andreas Röhler [this message]
2012-08-22 15:11 ` Stefan Monnier
2012-08-23 2:56 ` justinhj
2012-08-23 12:52 ` Deokhwan Kim
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