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Re: emacs-lisp/cl.el (pushnew): void-variable x

From: Stefan Monnier
Subject: Re: emacs-lisp/cl.el (pushnew): void-variable x
Date: Mon, 11 Sep 2006 23:25:47 -0400
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.0.50 (gnu/linux)

>>> But what's the wisdom behind pushnew-internal [we already know that
>>> PLACE is a symbol]?
>>> This is in case we someday switch to lexical binding.
>>> add-to-list won't work properly on lexical varables.
>> Ok, but why does it need a defvar ?

> That tells the compiler that pushnew-internal is a special (non-lexical)
> variable.

Honestly, I think using `add-to-list' here makes no sense.
Since we have the variable as a symbol and we're macro-expanding, we can
just use `(unless (member ,element ,var) (setq ,var (cons ,element ,var)))
That'll be a lot more efficient than going through a function call to
add-to-list, using an aux-var accessed via symbol-value and set and checking
`append' arg etc...

`add-to-list' is convenient for ~/.emacs and things like that, but I don't
think this use is appropriate.


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