Dynamic let for lexical scope?

Dynamic let for lexical scope?

[Hi-Angel]

I have the following function:

(defun sort-lines-nocase (beg end)
  (let ((sort-fold-case t))
    (sort-lines nil beg end)))

It temporarily changes sort-fold-case. Now, when compiled with

;;; -*- lexical-binding: t -*-

at the top, it causes a warning "Unused lexical variable ‘sort-fold-case’".

I wonder, how do I temporarily change the global sort-fold-case
symbol, and then change it back, aside of surrounding the code with
multiple setq?

Re: Dynamic let for lexical scope?

[Michael Heerdegen]

Hi-Angel <hiangel999@gmail.com> writes:

> I have the following function:
>
> (defun sort-lines-nocase (beg end)
>   (let ((sort-fold-case t))
>     (sort-lines nil beg end)))
>
> It temporarily changes sort-fold-case. Now, when compiled with
>
> ;;; -*- lexical-binding: t -*-
>
> at the top, it causes a warning "Unused lexical variable
> ‘sort-fold-case’".

The canonical answer is: add (defvar sort-fold-case) to get local
dynamical binding:

(defun sort-lines-nocase (beg end)
  (defvar sort-fold-case)
  (let ((sort-fold-case t))
    (sort-lines nil beg end)))

In your case, I guess the problem is that `sort-lines' is autoloaded and
the variable is not yet declared when you compile (or evaluate for the
first time).  So you could also add

  (eval-when-compile (require 'sort))

It's a matter of taste which alternative is better or cleaner.  If you
use more stuff from sort.el, it's probably better to `require' it.


Michael.

Re: Dynamic let for lexical scope?

[Hi-Angel]

Thank you!

On Wed, 13 Feb 2019 at 05:59, Michael Heerdegen
<michael_heerdegen@web.de> wrote:
>
> Hi-Angel <hiangel999@gmail.com> writes:
>
> > I have the following function:
> >
> > (defun sort-lines-nocase (beg end)
> >   (let ((sort-fold-case t))
> >     (sort-lines nil beg end)))
> >
> > It temporarily changes sort-fold-case. Now, when compiled with
> >
> > ;;; -*- lexical-binding: t -*-
> >
> > at the top, it causes a warning "Unused lexical variable
> > ‘sort-fold-case’".
>
> The canonical answer is: add (defvar sort-fold-case) to get local
> dynamical binding:
>
> (defun sort-lines-nocase (beg end)
>   (defvar sort-fold-case)
>   (let ((sort-fold-case t))
>     (sort-lines nil beg end)))
>
> In your case, I guess the problem is that `sort-lines' is autoloaded and
> the variable is not yet declared when you compile (or evaluate for the
> first time).  So you could also add
>
>   (eval-when-compile (require 'sort))
>
> It's a matter of taste which alternative is better or cleaner.  If you
> use more stuff from sort.el, it's probably better to `require' it.
>
>
> Michael.