Re: never use `eval'

["Pascal J. Bourguignon" <pjb@informatimago.com>]

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/
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