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Re: Building Emacs overflowed pure space

From: Stefan Monnier
Subject: Re: Building Emacs overflowed pure space
Date: Thu, 20 Jul 2006 00:07:42 -0400
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.0.50 (gnu/linux)

>     The setq can be placed after, but the cdr can't, in case the `body' does
>     a setcdr on it.

> It is (cdr ,temp), referring to the uninterned symbol.

(cdr ,temp) contains two operations: one is to look up the var to get its
content, and the other is to extract the cdr part of that content.  Only the
first part is protected by the fact that the symbol is uninterned.

> The body cannot refer to that uninterned symbol (that's the whole
> point of using one).

Indeed, but it may refer to the cons cell.

> So it is safe to take the cdr at the end.

Maybe it is, but it will subtly change the semantics in case the loop body
modifies the list it's loooping over.


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