[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: questioning let
From: |
David Kastrup |
Subject: |
Re: questioning let |
Date: |
Wed, 24 Feb 2010 19:10:38 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.1.92 (gnu/linux) |
Andreas Röhler <andreas.roehler@easy-emacs.de> writes:
> David Kastrup wrote:
>> Andreas Roehler <andreas.roehler@online.de> writes:
>>
>>> 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
> (?)
The warning is completely accurate since arg-extern can be called from
outside arg-setting, in which case it will assign to a global variable
called "arg".
Whether or not some let-binding might be effective at the point of
calling arg-extern is unknown to the compiler.
In a Lisp variant with lexical binding (like Common Lisp or Scheme),
arg-extern has no way to fiddle with the let-binding of arg-setting: it
is completely inaccessible by name outside of arg-setting itself.
--
David Kastrup
Re: questioning let, Pascal J. Bourguignon, 2010/02/24
Re: questioning let, Tim X, 2010/02/24