[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: never use `eval'
From: |
Pascal J. Bourguignon |
Subject: |
Re: never use `eval' |
Date: |
Fri, 17 Jul 2015 10:55:32 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) |
Barry Margolin <barmar@alum.mit.edu> writes:
> In article <87d1zrlfz6.fsf@kuiper.lan.informatimago.com>,
> "Pascal J. Bourguignon" <pjb@informatimago.com> wrote:
>> 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.
Oh! I see…
This is nice, to be able to pass an environment like this, because we
could write macros that would build a "lexical environment" to be passed
to eval…
--
__Pascal Bourguignon__ http://www.informatimago.com/
“The factory of the future will have only two employees, a man and a
dog. The man will be there to feed the dog. The dog will be there to
keep the man from touching the equipment.” -- Carl Bass CEO Autodesk
- Re: never use `eval' (was: Re: How to mapcar or across a list?), (continued)
- Message not available
- Re: never use `eval' (was: Re: How to mapcar or across a list?), Barry Margolin, 2015/07/15
- Message not available
- Re: never use `eval' (was: Re: How to mapcar or across a list?), Barry Margolin, 2015/07/15
- Re: never use `eval' (was: Re: How to mapcar or across a list?), Emanuel Berg, 2015/07/15
- Re: never use `eval' (was: Re: How to mapcar or across a list?), Emanuel Berg, 2015/07/16
- Message not available
- Re: never use `eval', Pascal J. Bourguignon, 2015/07/16
- Re: never use `eval', Emanuel Berg, 2015/07/16
- Re: never use `eval', Barry Margolin, 2015/07/17
- Re: never use `eval',
Pascal J. Bourguignon <=
- Message not available
- Re: never use `eval', Pascal J. Bourguignon, 2015/07/15
- Re: never use `eval', Emanuel Berg, 2015/07/15
Re: How to mapcar or across a list?, Pascal J. Bourguignon, 2015/07/15
Re: How to mapcar or across a list?, Barry Margolin, 2015/07/15