From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Nathan Trapuzzano <nbtrap@nbtrap.com>
Cc: emacs-devel@gnu.org
Subject: Re: Double unquote/unquote-splicing
Date: Mon, 04 Nov 2013 12:27:00 -0500 [thread overview]
Message-ID: <jwv1u2wks69.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <87wqko6z8g.fsf@nbtrap.com> (Nathan Trapuzzano's message of "Mon, 04 Nov 2013 09:03:11 -0500")
> (defmacro once-only (names &rest body)
> (let ((gensyms (loop for n in names collect (gensym))))
> `(let (,@(loop for g in gensyms collect `(,g (gensym))))
> `(let (,,@(loop for g in gensyms for n in names collect ``(,,g ,,n)))
> ,(let (,@(loop for n in names for g in gensyms collect `(,n ,g)))
> ,@body)))))
There are two reasons why I'm resisting it:
1- the above code looks clean, but I can't understand it at all.
Your alternative code is less clean and not easy to understand, but
I *can* understand it.
2- Since we don't allow (\` (a (\, 1 2 3))), it's weird to allow
``(a ,,@x) since one possible expansion for it when x=(1 2 3) is
(\` (a (\, 1 2 3))).
Another way to say it is that we should allow (\, 1 2 3) and (\,@
1 2 3), but that can't be used with the ,e and ,@e syntax, so it'll
stay as a second-rate citizen.
Isn't the above the same as
(defmacro once-only (names &rest body)
(let ((gensyms (loop for n in names collect (gensym))))
`(let (,@(loop for g in gensyms collect `(,g (gensym))))
`(let (,@(list ,@(loop for g in gensyms for n in names collect ``(,,g ,,n))))
,(let (,@(loop for n in names for g in gensyms collect `(,n ,g)))
,@body)))))
-- Stefan
next prev parent reply other threads:[~2013-11-04 17:27 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-04 14:03 Double unquote/unquote-splicing Nathan Trapuzzano
2013-11-04 17:27 ` Stefan Monnier [this message]
2013-11-04 17:59 ` Nathan Trapuzzano
2013-11-04 18:11 ` Nathan Trapuzzano
2013-11-04 18:33 ` Stefan Monnier
2013-11-04 19:01 ` Drew Adams
2013-11-04 19:09 ` Nathan Trapuzzano
2013-11-04 20:41 ` Stefan Monnier
2013-11-05 15:03 ` Nathan Trapuzzano
2013-11-05 19:14 ` Stefan Monnier
2013-11-05 4:01 ` Stephen J. Turnbull
2013-11-05 15:22 ` Nathan Trapuzzano
2013-11-05 21:48 ` Stephen J. Turnbull
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