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Re: questioning let

From: Pascal J. Bourguignon
Subject: Re: questioning let
Date: Thu, 25 Feb 2010 00:41:41 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (darwin)

Andreas Röhler <address@hidden> writes:

> David Kastrup wrote:
>> Andreas Roehler <address@hidden> writes:
>>> Hi,
>>> behaviour of the example code below puzzles me. Would
>>> expect setting of arg by external function, but inside
>>> `let', recognised. But remains `1'.
>>> (defun arg-setting ()
>>>   (interactive)
>>>   (let ((arg 1))
>>>     (message "%s" arg)
>>>     (arg-extern arg)
>>>     (message "%s" arg)))
>>> (defun arg-extern (arg)
>>>   (setq arg (1- arg)))
>>> Any help?
>> The argument binding in arg-extern is the innermost one and consequently
>> the only affected one.  If you make the function argument-less, it will
>> likely work as expected by you, affecting the binding in arg-setting.
> That works, thanks a lot!
> However, stored in some eil.el, get a compiler warning than:
> In arg-extern:
> eil.el:9:9:Warning: reference to free variable `arg'
> eil.el:9:17:Warning: assignment to free variable `arg'
> Would think a useless warning, as the compiler should know being inside a let 
> (?)

Yes, as I said, this is something that you shoudl avoid, and the
compiler is of the same opinion.

__Pascal Bourguignon__

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