From: Barry Margolin <barmar@alum.mit.edu>
To: help-gnu-emacs@gnu.org
Subject: Re: never use `eval'
Date: Fri, 17 Jul 2015 04:36:06 -0400 [thread overview]
Message-ID: <barmar-352758.04360617072015@88-209-239-213.giganet.hu> (raw)
In-Reply-To: 87d1zrlfz6.fsf@kuiper.lan.informatimago.com
In article <87d1zrlfz6.fsf@kuiper.lan.informatimago.com>,
"Pascal J. Bourguignon" <pjb@informatimago.com> wrote:
> Emanuel Berg <embe8573@student.uu.se> writes:
>
> > Remember when I said the byte compiler should be more
> > offensive and offer more elaborate style warnings?
> >
> > And this is a good example of that!
> >
> > Even in the Emacs help
> >
> > (describe-function 'eval)
> >
> > it doesn't say anything about the dangers of the
> > "nil environment":
> >
>
> (eval FORM &optional LEXICAL)
>
> > Evaluate FORM and return its value.
> > If LEXICAL is t, evaluate using lexical scoping.
> > LEXICAL can also be an actual lexical environment,
> > in the form of an alist mapping symbols to
> > their value.
>
> Doesn't seem to work:
>
> (setf lexical-binding t)
>
> (let ((x 42))
> (eval 'x t))
> Debugger entered--Lisp error: (void-variable x)
>
> (let ((x 42))
> (eval 'x nil))
> Debugger entered--Lisp error: (void-variable x)
I don't think that could be expected to work. Since eval is a function,
not a special form, there's no way it can access the lexical environment
outside it. I assume the LEXICAL parameter means that it implements
lexical binding in the code being evaluated, e.g. if you do:
(eval '(let ((x 42)) x) t)
it binds x lexically, not dynamically.
But it also says that LEXICAL can be an alist, so you could do:
(eval 'x '((x . 42)))
and it should return 42.
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
next prev parent reply other threads:[~2015-07-17 8:36 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-15 20:14 How to mapcar or across a list? Marcin Borkowski
2015-07-15 20:42 ` Rasmus
2015-07-15 20:55 ` Marcin Borkowski
2015-07-15 22:21 ` Emanuel Berg
2015-07-15 22:21 ` John Mastro
[not found] ` <mailman.6977.1436998965.904.help-gnu-emacs@gnu.org>
2015-07-15 22:28 ` Pascal J. Bourguignon
2015-07-15 22:36 ` Emanuel Berg
2015-07-15 22:57 ` never use `eval' (was: Re: How to mapcar or across a list?) Emanuel Berg
2015-07-15 23:27 ` John Mastro
2015-07-15 23:57 ` Emanuel Berg
2015-07-16 0:18 ` John Mastro
[not found] ` <mailman.6984.1437004760.904.help-gnu-emacs@gnu.org>
2015-07-16 0:04 ` Barry Margolin
[not found] ` <mailman.6982.1437001117.904.help-gnu-emacs@gnu.org>
2015-07-16 0:01 ` Barry Margolin
2015-07-16 1:13 ` Emanuel Berg
2015-07-17 0:55 ` Emanuel Berg
[not found] ` <mailman.7027.1437094623.904.help-gnu-emacs@gnu.org>
2015-07-17 1:39 ` never use `eval' Pascal J. Bourguignon
2015-07-17 2:16 ` Emanuel Berg
2015-07-17 8:36 ` Barry Margolin [this message]
2015-07-17 8:55 ` Pascal J. Bourguignon
2015-07-16 0:22 ` Pascal J. Bourguignon
2015-07-16 1:11 ` Emanuel Berg
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