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