An MRE or other hints for this macro / dynamic scoping bug?

An MRE or other hints for this macro / dynamic scoping bug?

[Dave Goel]

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Hey Emacsers,

I'm likely losing my mind. Is this not a bug, below?

I tried discussing on #emacs first, and then reported (a slightly more
complex version). But, it's perhaps not obvious, and it  was suggested I
try to produce a simpler example.

I realize I should have discussed it here first, before reporting it.  A
discussion here would probably produce a much better bug report in any
case.

Do you guys see an obvious bug here? Any simpler versions you can think
of?  Any hints where the bug could lie?

Basically, I define a macro that hardcodes the value of our variable ii
that existed before the macro definition.

And, then try to use it.


(progn
  (setq lexical-binding nil)

  (dotimes (ii 10)
    (defmacro mac ()
      `(message "%S" ,ii)
      )
    (mac)))


That's the code.
Eval it once. Works.
Eval it again. Works.

Eval it the third time. Debugger entered. Tested in emacs -Q in 28 and 29.
[[a]]

In fact, before you eval it the third time, if you change ii to jj, it
still complains about ii. [[b]]

Bugs are the behaviors  (a) and (b) above.

The macro expands to (list 'message "%S" ii). That should have worked,
right? Because ii was already set at the time of definition?

Here's the debugger behavior -
Debugger entered--Lisp error: (void-variable ii)
  (list 'message "%S" ii)

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Re: An MRE or other hints for this macro / dynamic scoping bug?

[Andreas Schwab]

How do you eval it?

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Re: An MRE or other hints for this macro / dynamic scoping bug?

[Stefan Kangas]

Dave Goel <deego3@gmail.com> writes:

> I realize I should have discussed it here first, before reporting it.  A
> discussion here would probably produce a much better bug report in any
> case.

Actually, a bug report is much better so that we can track the progress.

In this case, we already have Bug#66940, so I recommend reporting your
findings there.  A new thread on emacs-devel at this point will just
make the discussion harder to follow.

Re: An MRE or other hints for this macro / dynamic scoping bug?

[Dave Goel]

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C-x C-e at the end of the block of the code.
Also, regarding bug (b) - we changed every instance of ii to jj. Yet it
complained about a ghost ii.


On Sun, Nov 5, 2023 at 3:04 PM Andreas Schwab <schwab@linux-m68k.org> wrote:

> How do you eval it?
>
> --
> Andreas Schwab, schwab@linux-m68k.org
> GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
> "And now for something completely different."
>

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Re: An MRE or other hints for this macro / dynamic scoping bug?

[Andreas Schwab]

Use M-x ielm instead.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."