From mboxrd@z Thu Jan  1 00:00:00 1970
Path: news.gmane.org!not-for-mail
From: Thien-Thi Nguyen <ttn@gnu.org>
Newsgroups: gmane.emacs.devel
Subject: Re: Sweeter Emacs Lisp
Date: Tue, 23 Jul 2013 06:37:50 +0200
Message-ID: <8738r5zyap.fsf@zigzag.favinet>
References: <8738rh6ftk.fsf@gnu.org> <jwvli4yy6rv.fsf-monnier+emacs@gnu.org>
	<87a9lezh9w.fsf@zigzag.favinet>
	<jwv4nbmwbur.fsf-monnier+emacs@gnu.org>
NNTP-Posting-Host: plane.gmane.org
Mime-Version: 1.0
Content-Type: multipart/signed; boundary="=-=-=";
	micalg=pgp-sha1; protocol="application/pgp-signature"
X-Trace: ger.gmane.org 1374554116 10127 80.91.229.3 (23 Jul 2013 04:35:16 GMT)
X-Complaints-To: usenet@ger.gmane.org
NNTP-Posting-Date: Tue, 23 Jul 2013 04:35:16 +0000 (UTC)
To: emacs-devel <emacs-devel@gnu.org>
Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Tue Jul 23 06:35:17 2013
Return-path: <emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org>
Envelope-to: ged-emacs-devel@m.gmane.org
Original-Received: from lists.gnu.org ([208.118.235.17])
	by plane.gmane.org with esmtp (Exim 4.69)
	(envelope-from <emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org>)
	id 1V1UJh-0001vT-GG
	for ged-emacs-devel@m.gmane.org; Tue, 23 Jul 2013 06:35:17 +0200
Original-Received: from localhost ([::1]:54647 helo=lists.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org>)
	id 1V1UJh-0004uD-0U
	for ged-emacs-devel@m.gmane.org; Tue, 23 Jul 2013 00:35:17 -0400
Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:41325)
	by lists.gnu.org with esmtp (Exim 4.71) (envelope-from <ttn@gnu.org>)
	id 1V1UJc-0004tf-St
	for emacs-devel@gnu.org; Tue, 23 Jul 2013 00:35:14 -0400
Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <ttn@gnu.org>) id 1V1UJb-0005ZR-HL
	for emacs-devel@gnu.org; Tue, 23 Jul 2013 00:35:12 -0400
Original-Received: from smtp207.alice.it ([82.57.200.103]:47723)
	by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from <ttn@gnu.org>)
	id 1V1UJb-0005W5-5r
	for emacs-devel@gnu.org; Tue, 23 Jul 2013 00:35:11 -0400
Original-Received: from zigzag.favinet (95.236.25.26) by smtp207.alice.it (8.6.060.26)
	id 51DA965502C3CEFE for emacs-devel@gnu.org;
	Tue, 23 Jul 2013 06:35:09 +0200
Original-Received: from ttn by zigzag.favinet with local (Exim 4.72)
	(envelope-from <ttn@gnu.org>) id 1V1UMK-0006Kh-Tk
	for emacs-devel@gnu.org; Tue, 23 Jul 2013 06:38:01 +0200
Mail-Followup-To: emacs-devel@gnu.org
In-Reply-To: <jwv4nbmwbur.fsf-monnier+emacs@gnu.org> (Stefan Monnier's message
	of "Mon, 22 Jul 2013 17:04:04 -0400")
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)
X-detected-operating-system: by eggs.gnu.org: Genre and OS details not
	recognized.
X-Received-From: 82.57.200.103
X-BeenThere: emacs-devel@gnu.org
X-Mailman-Version: 2.1.14
Precedence: list
List-Id: "Emacs development discussions." <emacs-devel.gnu.org>
List-Unsubscribe: <https://lists.gnu.org/mailman/options/emacs-devel>,
	<mailto:emacs-devel-request@gnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/archive/html/emacs-devel>
List-Post: <mailto:emacs-devel@gnu.org>
List-Help: <mailto:emacs-devel-request@gnu.org?subject=help>
List-Subscribe: <https://lists.gnu.org/mailman/listinfo/emacs-devel>,
	<mailto:emacs-devel-request@gnu.org?subject=subscribe>
Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org
Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org
Xref: news.gmane.org gmane.emacs.devel:162083
Archived-At: <http://permalink.gmane.org/gmane.emacs.devel/162083>

--=-=-=
Content-Type: text/plain
Content-Transfer-Encoding: quoted-printable

() Stefan Monnier <monnier@iro.umontreal.ca>
() Mon, 22 Jul 2013 17:04:04 -0400

   > RMS suggested instead:
   >  (cond VAR (CONDITION [BODY...])
   >            ...)

   As I pointed out back then, a more general solution is a way to
   let-bind new variables in between cond clauses, as in

      (cond
       (<test1> <body1>)
       (let x <foo>)
       (<test2> <body2>))

   which would be used in cases where we currently use

      (let (x)
        (cond
         (<test1> <body1>)
         ((progn (setq x <foo>) <test2>) <body2>))

Yes, i see this can be used as the basis of the other forms.  Cool.
Has anyone done a C implementation?  Here's a sketch (in *scratch*):

 (defmacro cool-cond (&rest clauses)
   (let ((rev (reverse clauses))
         one elab)
     (while (setq one (pop rev))
       (setq elab (pcase one
                    (`(let ,var ,exp)
                     `((t (let ((,var ,exp))
                            (cond ,@elab)))))
                    (`(let ,var)
                     `((t (let (,var)
                            (cond ,@elab)))))
                    (_ (cons one elab)))))
     `(cond ,@elab)))
=20
 (macroexpand '(cool-cond
                (nil t)=20
                (t nil)))
 (cond
  (nil t)
  (t nil))
=20
 (macroexpand '(cool-cond
                (let bar 'none)
                (nil t)=20
                (let foo (list bar 42))
                (foo)
                (t nil)))
 (cond
  (t
   (let
       ((bar 'none))
     (cond
      (nil t)
      (t
       (let
           ((foo
             (list bar 42)))
         (cond
          (foo)
          (t nil))))))))

=2D-=20
Thien-Thi Nguyen
   GPG key: 4C807502
   (if you're human and you know it)
      read my lisp: (responsep (questions 'technical)
                               (not (via 'mailing-list)))
                     =3D> nil

--=-=-=
Content-Type: application/pgp-signature

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.10 (GNU/Linux)

iEYEARECAAYFAlHuCKEACgkQZwMiJEyAdQLG4wCeMC6w6yGhHg+iuM0+ZL5lUGMy
njoAoMzwFy06uUgyEZo+FjdJ+lKA/TV8
=4hRj
-----END PGP SIGNATURE-----
--=-=-=--