From: "Basil L. Contovounesios" <contovob@tcd.ie>
To: akater <nuclearspace@gmail.com>
Cc: emacs-devel@gnu.org
Subject: Re: defmacro with built-in gensym declaration and initialization
Date: Wed, 20 Jan 2021 20:55:46 +0000 [thread overview]
Message-ID: <87o8hj9vl9.fsf@tcd.ie> (raw)
In-Reply-To: <878s8n76ih.fsf@gmail.com> (akater's message of "Wed, 20 Jan 2021 19:28:06 +0000")
akater <nuclearspace@gmail.com> writes:
> "Basil L. Contovounesios" <contovob@tcd.ie> writes:
>
>> IMO, this minor convenience is insufficient motivation for
>> conflating/complicating a macro's global arglist, i.e. its arity,
>> calling convention, etc., with utilities for its local body. Is there
>> some other motivation? Am I missing something?
>
> My motivation mostly comes from CL where complicated lambda lists are
> not considered an issue, and it didn't come to my mind it could be an
> issue for Emacs Lisp users. In particular, &gensym does indeed follow
> the design of &aux, described below as “hideous” (another surprise).
I'd seen &aux before but didn't look up what it does until now, and I
must say I share Stefan's sentiment :).
> I use &aux regularly, and I find it a nice addition as it reduces the
> nesting depth of defun and defmacro forms. &gensym does that and saves
> some boilerplate on top of it, I tried it in real life macros, found it
> useful, and that's pretty much it.
Let's just say I would sooner see native arglists gain support for
keyword arguments ;).
For non-native arglists, we could always extend cl-defmacro or some
other definition definer.
>> conflating/complicating a macro's global arglist, i.e. its arity,
>
> What's the arity of defmacro? This form already allows any number of
> arguments so as far as I can see adding another keyword does not change
> arity. Calling convention is backwards compatible.
I was referring to the arity of the macro being defined, not that of
defmacro.
> Again, Common Lisp
> implementations are allowed to introduce their own lambda list keywords
> so I didn't (and still don't) think extending lambda-list keywords set
> is a big deal.
I can't imagine it being as little a deal in Elisp, but that's just my
impression.
>> Why not provide handy gensym/once-only local conveniences for macro
>> authors instead (some of which already exist in one form or another,
>> e.g. macroexp-let2, inline-letevals, and org-with-gensyms)?
>
> I don't have much experience with macroexp-let2 which on the first
> glance looks like an overcomplicated once-only that is mostly relevant
> for functions that are meant to be byte-compiled.
It and its variant macroexp-let2* are relevant wherever the macro author
wants to avoid evaluating an argument more than once, but improvements
are always welcome.
> Since we're moving to
> natively compiled Elisp, I was thinking it's going to become less
> relevant in near future, and &gensym covers most use cases of once-only.
I don't see how native compilation changes how existing and new Elisp
macros ought to be written.
> Again, org-with-gensyms is precisely something that's being replaced
> here with an alternative that is less verbose and has a decreased
> nesting depth.
Just my 2 cents,
--
Basil
next prev parent reply other threads:[~2021-01-20 20:55 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-20 8:15 defmacro with built-in gensym declaration and initialization akater
2021-01-20 13:46 ` Basil L. Contovounesios
2021-01-20 15:09 ` Stefan Monnier
2021-01-20 16:47 ` Robin Tarsiger
2021-01-20 19:28 ` akater
2021-01-20 20:55 ` Basil L. Contovounesios [this message]
2021-01-21 19:34 ` akater
2021-01-21 20:50 ` Stefan Monnier
2021-01-21 20:50 ` Basil L. Contovounesios
2021-01-21 21:05 ` Stefan Monnier
2021-01-21 21:23 ` Basil L. Contovounesios
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