bug#66940: closed (Dynamic scoping is all weird now?)

[GNU bug Tracking System]

Your message dated Wed, 08 Nov 2023 04:08:10 +0100
with message-id <87fs1h7xid.fsf@web.de>
and subject line Re: bug#66940: Dynamic scoping is all weird now?
has caused the debbugs.gnu.org bug report #66940,
regarding Dynamic scoping is all weird now?
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs@gnu.org.)


-- 
66940: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=66940
GNU Bug Tracking System
Contact help-debbugs@gnu.org with problems

--- Begin Message --- Subject: Dynamic scoping is all weird now? Date: Sun, 5 Nov 2023 00:06:49 -0400

I was playing around, checking my sanity re : dynamic scoping.  I'm probably rusty, but I could swear that on older emacsen, this sort of code would print 33 ten times. 

On emacs -Q with debian stable (28.2).
I try this

(progn
  (setq lexical-binding nil)

  (dotimes (ii 10)
    (defmacro mac ()
      `(message "%S" ,ii)
      (sit-for 0.1))
    (let ((old_ii ii))
      (setq ii 33)
      (mac)
      (setq ii old_ii)
      )))

Exits without error the first two times, although, strangely, i don't see any messages the second time. (I expected to see ten 33's).

(a) As in, the second time, it doesn't print 33 ten times, as we would expect.

(b) The third time is stranger. 
Let's evaluate it a third time! The third time is even weirder.

The third time, it complains
Debugger entered--Lisp error: (void-variable ii)
  (list 'message "%S" ii)
  (lambda nil (list 'message "%S" ii) (list 'print ii) (sit-for 0.1))()
  macroexpand((mac) nil)
  macroexp-macroexpand((mac) nil)
  macroexp--expand-all((mac))
  macroexp--all-forms(((setq ii 33) (mac) (setq ii old_ii)))
  macroexp--expand-all((let ((old_ii ii)) (setq ii 33) (mac) (setq ii old_ii)))

and so on.

The bug(?) was reproduced on 29.1 as well - by e1f on #emacs

(c) It gets even funnier. e1f changed ii to var, but the third time, it still complained about ii, with the above error message, and not about var.  I reproduced that as well.

Dave

--- End Message ---

> --- Begin Message ---
>
>
>
> Subject: 
>
> Re: bug#66940: Dynamic scoping is all weird now?
>
>
>
>
> Date: 
>
> Wed, 08 Nov 2023 04:08:10 +0100
>
>
>
>
> User-agent: 
>
> Gnus/5.13 (Gnus v5.13)
>
>
>
>
> Dave Goel <deego3@gmail.com> writes:
>
> > Thank you
>
> Then let's close this one.
>
> What I still wanted to say (to you): no need to complicate things using
> macros here in your example.  Use functions, then variable references
> are simple and clear.
>
> If a macro (expansion) needs to refer to run-time values, use macro
> arguments to pass an appropriate expression (like a variable).
>
> But this is overkill in your case, no macros needed.  The purpose of
> Lisp macros is to extend the language and/or rewrite code (at compile
> time).  More or less, only that.  Always think twice if you really need
> macros, try to avoid using macros when possible.  This will make the
> code easier to understand and maintain.  Only if a macro introduces an
> abstraction that makes the code actually easier to understand justifies
> using one.
>
> Michael.
>
>
> --- End Message ---