Re: Real-life examples of lexical binding in Emacs Lisp

[Pascal J. Bourguignon]

"Pascal J. Bourguignon" <pjb@informatimago.com> writes:

> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>
>>>> However, I would argue that for global variables, lexical binding would
>>>> be useful too, even by default.
>>
>> I'm not sure what that means.  But you can set a global value to
>> a variable without declaring it as dynamically scoped:
>>
>>     (setq my-lex-var 3)
>
> Wrong.

Not.

> Having a file lex.el:
> ------------------------------------------------------------------------
> ;; -*- mode:emacs-lisp; lexical-binding:nil -*-
>
> (setq lexical? 33)
> (defun f ()
>   lexical?)
> (defun g ()
>   (let ((lexical? 42))
>     (f)))
>
> (print (g))
> ------------------------------------------------------------------------
>
> Then M-x load-file RET lex.el RET writes 42 in *Message* which shows
> that lexical? IS a dynamic variable!  If it was lexical, we would get
> 33, because the lexical scope of the closure f is the global scope,
> where lexical? as been bound to 33, not the local dynamic scope of the
> function g when the variable lexical? is bound to 42.

Oops, sorry, I intended to run two tests.  With lexical-binding:t
indeed, setq defines the global variable and leaves it lexical.

Reloading the file with lexical-binding:t even suppresses the dynamic
aspect of a previously defined (with defvar) dynamic variable.


-- 
__Pascal Bourguignon__                 http://www.informatimago.com/
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