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

["Andreas Röhler" <andreas.roehler@easy-emacs.de>]

Am 29.05.2015 um 14:28 schrieb Pascal J. Bourguignon:
> Marcin Borkowski <mbork@mbork.pl> writes:
>
>> Hi all,
>>
>> I googled a bit, and could not find /real-world/ examples of using
>> lexical binding and its advantages /in Emacs Lisp/.  I understand that
>> it's a nice thing to be able to create closures, and that lexical
>> binding is in general faster than dynamic binding (which is a bonus in
>> itself), but could anyone show me a real /text editing/ problem that
>> lexical binding solves, like something that is easier done with
>> l.b. than with d.b.?  (Examples of general-purpose programming problems
>> made easier with l.b. are more or less obvious/easy to find, but Emacs
>> is a text editor, after all, and this is its primary area.)
> Lexical binding matters for two things:
>
> - it allows the creation of closures.
> - it prevents the clobbering of variables.
>
>
> Closures:
>
>      A typical example, is visible in the thread "~`symbol-function' to
>      get code as list even when byte-compiled?":
>
>      ;;;; -*- mode:emacs-lisp;lexical-binding:t;coding:utf-8 -*-
>      (defun add-one-shot-meat (hook fun)
>        (let ((name (gensym)))
>          (setf (symbol-function name)
>                (lambda ()
>                  (remove-hook hook name)
>                  (funcall fun)))
>          (add-hook hook name)))
>
>      Without lexical binding, fun and hook would be dynamic, and
>      therefore their bindings would disappear when add-one-shot-meat
>      returns.  Therefore they would be undefined variable when the
>      function is called, or worse, they may be bound at that time by some
>      other function to something different.
>
>      Compare:
>
>          (setf lexical-binding t)
>
>          (defun e (f)
>            (let ((v 42))
>               (funcall f)))
>
>          (let ((v 33))
>            (e (lambda () v)))
>
>          --> 33
>
>
>          (setf lexical-binding nil)
>
>          (defun e (f)
>            (let ((v 42))
>               (funcall f)))
>
>          (let ((v 33))
>            (e (lambda () v)))
>
>          --> 42
>
>

Thanks a lot all! Will take some time to work through the examples given.

Cheers,

Andreas