Re: Surrounding Lexical Variable Reference in the Body of defun

["Andreas Röhler" <andreas.roehler@easy-emacs.de>]

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?