From: Deokhwan Kim <deokhwankim@gmail.com>
To: help-gnu-emacs@gnu.org
Subject: Surrounding Lexical Variable Reference in the Body of defun
Date: Mon, 20 Aug 2012 23:07:00 -0700 (PDT) [thread overview]
Message-ID: <8b43586d-2ad4-4cf6-ae15-446e909bf496@googlegroups.com> (raw)
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
next reply other threads:[~2012-08-21 6:07 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-21 6:07 Deokhwan Kim [this message]
2012-08-22 6:42 ` Surrounding Lexical Variable Reference in the Body of defun Andreas Röhler
2012-08-22 15:11 ` Stefan Monnier
2012-08-23 2:56 ` justinhj
2012-08-23 12:52 ` Deokhwan Kim
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