bug#52147: Eager macro-expansion is not performed in `eval-and-compile' functions

bug#52147: Eager macro-expansion is not performed in `eval-and-compile' functions

[Paul Pogonyshev]

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Simple code to demonstrate this:

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

(defmacro my-macro (x)
  `,x)

(eval-and-compile
  (defun my-func-eac (what)
    (my-macro what)))

(defun my-func-normal (what)
  (my-macro what))

(print (symbol-function 'my-func-eac))
(print (symbol-function 'my-func-normal))

`eval-and-compile' is advertised in Elisp manual to make byte-compilation
of certain macros without prior loading possible. Looks strange that at the
same time it can worsen performance of non-byte-compiled code.

Paul

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bug#52147: Eager macro-expansion is not performed in `eval-and-compile' functions

[Michael Heerdegen]

Hello Paul,

> (eval-and-compile
>   (defun my-func-eac (what)
>     (my-macro what)))
>
> (defun my-func-normal (what)
>   (my-macro what))
>
> (print (symbol-function 'my-func-eac))
> (print (symbol-function 'my-func-normal))
>
> `eval-and-compile' is advertised in Elisp manual to make
> byte-compilation of certain macros without prior loading
> possible. Looks strange that at the same time it can worsen
> performance of non-byte-compiled code.

Is the issue you want to draw attention to that an interpreted
`eval-and-compile' form doesn't macroexpand its body?

Michael.

bug#52147: Eager macro-expansion is not performed in `eval-and-compile' functions

[Paul Pogonyshev]

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That's what the subject says. I know that it works regardless, but the
performance suffers, especially if the used macros are complex.

Paul

On Sun, 28 Nov 2021 at 11:30, Michael Heerdegen <michael_heerdegen@web.de>
wrote:

> Hello Paul,
>
> > (eval-and-compile
> >   (defun my-func-eac (what)
> >     (my-macro what)))
> >
> > (defun my-func-normal (what)
> >   (my-macro what))
> >
> > (print (symbol-function 'my-func-eac))
> > (print (symbol-function 'my-func-normal))
> >
> > `eval-and-compile' is advertised in Elisp manual to make
> > byte-compilation of certain macros without prior loading
> > possible. Looks strange that at the same time it can worsen
> > performance of non-byte-compiled code.
>
> Is the issue you want to draw attention to that an interpreted
> `eval-and-compile' form doesn't macroexpand its body?
>
> Michael.
>

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bug#52147: Eager macro-expansion is not performed in `eval-and-compile' functions

[Lars Ingebrigtsen]

Paul Pogonyshev <pogonyshev@gmail.com> writes:

 > Is the issue you want to draw attention to that an interpreted
 > `eval-and-compile' form doesn't macroexpand its body?

> That's what the subject says.

Well, not exactly -- it doesn't say anything about the code being
interpreted.

> I know that it works regardless, but the
> performance suffers, especially if the used macros are complex.

We usually don't stress a lot about the performance of interpreted
(i.e., uncompiled) code.  Does this have a performance impact on
byte-compiled code?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#52147: Eager macro-expansion is not performed in `eval-and-compile' functions

[Michael Heerdegen]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> We usually don't stress a lot about the performance of interpreted
> (i.e., uncompiled) code.

Well we do, a bit,

  (info "(elisp) How Programs Do Loading")

says that loading a file performs eager macro expansion and that does
speed up the resulting code.  `eval', `eval-when-compile' and
`eval-and-compile' don't perform eager macro expansion.  I don't know to
what degree this is on purpose.  But if a macro is defined later in the
file or in another file that has not yet been loaded this may not be
possible anyway.

Michael.

bug#52147: Eager macro-expansion is not performed in `eval-and-compile' functions

[Lars Ingebrigtsen]

Michael Heerdegen <michael_heerdegen@web.de> writes:

> Well we do, a bit,
>
>   (info "(elisp) How Programs Do Loading")
>
> says that loading a file performs eager macro expansion and that does
> speed up the resulting code.  `eval', `eval-when-compile' and
> `eval-and-compile' don't perform eager macro expansion.  I don't know to
> what degree this is on purpose.  But if a macro is defined later in the
> file or in another file that has not yet been loaded this may not be
> possible anyway.

It sounds to me like things are basically working as designed.

Perhaps Stefan has some comments; added to the CCs.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#52147: Eager macro-expansion is not performed in `eval-and-compile' functions

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

>>> We usually don't stress a lot about the performance of interpreted
>>> (i.e., uncompiled) code.

Indeed.

>> Well we do, a bit,
>>
>>   (info "(elisp) How Programs Do Loading")
>>
>> says that loading a file performs eager macro expansion and that does
>> speed up the resulting code.  `eval', `eval-when-compile' and
>> `eval-and-compile' don't perform eager macro expansion.  I don't know to
>> what degree this is on purpose.  But if a macro is defined later in the
>> file or in another file that has not yet been loaded this may not be
>> possible anyway.
>
> It sounds to me like things are basically working as designed.
>
> Perhaps Stefan has some comments; added to the CCs.

AFAIK the exact time of macro expansion is left underspecified
on purpose.  Whether eager-macroexpansion is used or not should be an
implementation detail.  A piece of code which relies on macro-expansion
being done lazily is a bug, AFAIC.  Usually those bugs become apparent
when byte-compiling the file (where macro-expansion is necessarily
eager), except for those cases that occur during bootstrap.

Both `eval-when-compile` and `eval-and-compile` currently defer to
`eval`, but they should arguably do the macro-expansion eagerly, indeed.

`eval` currently doesn't use eager macro-expansion because I haven't
done the work needed to check/ensure that the resulting potential
slowdown is negligible.  But I think `eval` should also eagerly
macro-expand its argument.


        Stefan

bug#52147: Eager macro-expansion is not performed in `eval-and-compile' functions

[Lars Ingebrigtsen]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> Both `eval-when-compile` and `eval-and-compile` currently defer to
> `eval`, but they should arguably do the macro-expansion eagerly, indeed.

OK; I'll leave this bug report open as a wishlist item.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no