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From: Thien-Thi Nguyen <ttn@gnu.org>
To: emacs-devel <emacs-devel@gnu.org>
Subject: Re: Sweeter Emacs Lisp
Date: Tue, 23 Jul 2013 06:37:50 +0200	[thread overview]
Message-ID: <8738r5zyap.fsf@zigzag.favinet> (raw)
In-Reply-To: <jwv4nbmwbur.fsf-monnier+emacs@gnu.org> (Stefan Monnier's message of "Mon, 22 Jul 2013 17:04:04 -0400")

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() 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)))
 
 (macroexpand '(cool-cond
                (nil t) 
                (t nil)))
 (cond
  (nil t)
  (t nil))
 
 (macroexpand '(cool-cond
                (let bar 'none)
                (nil t) 
                (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))))))))

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

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  reply	other threads:[~2013-07-23  4:37 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-07-14  2:22 Sweeter Emacs Lisp fgallina
2013-07-14 11:36 ` Dmitry Gutov
2013-07-14 11:53   ` Vitalie Spinu
2013-07-14 12:38     ` Aurélien Aptel
2013-07-14 13:25     ` Xue Fuqiao
2013-07-14 14:16     ` Pascal J. Bourguignon
2013-07-14 14:22 ` Lars Magne Ingebrigtsen
2013-07-14 16:27   ` Juanma Barranquero
2013-07-14 19:43     ` Lars Magne Ingebrigtsen
2013-07-15  3:20   ` Dmitry Gutov
2013-07-15  5:03     ` Stephen J. Turnbull
2013-07-16 20:23       ` Dmitry Gutov
2013-07-17 14:04         ` Lars Magne Ingebrigtsen
2013-07-17 15:07           ` Dmitry Gutov
2013-07-16  2:15   ` Miles Bader
2013-07-16  9:12     ` Stefan Monnier
2013-07-14 16:18 ` Josh
2013-07-14 16:30   ` Juanma Barranquero
2013-07-14 17:14     ` Josh
2013-07-14 17:18       ` Juanma Barranquero
2013-07-15  6:05         ` Lars Brinkhoff
2013-07-15  7:04   ` Stefan Monnier
2013-07-15 13:30     ` Bozhidar Batsov
2013-07-16  2:26       ` Miles Bader
2013-07-16  6:08         ` Thien-Thi Nguyen
2013-07-16 14:07           ` Drew Adams
2013-07-16  9:11       ` Stefan Monnier
2013-07-14 17:24 ` Andreas Schwab
2013-07-16  2:13 ` Miles Bader
2013-07-16  6:14   ` Stephen J. Turnbull
2013-07-16  9:07   ` Stefan Monnier
2013-07-16 11:09     ` Juanma Barranquero
2013-07-16 12:25       ` Andreas Schwab
2013-07-16 13:04         ` Thierry Volpiatto
2013-07-16 13:42         ` Juanma Barranquero
2013-07-16 14:38           ` Andreas Schwab
2013-07-16 14:42             ` Juanma Barranquero
2013-07-16 20:57       ` Stefan Monnier
2013-07-22 15:24 ` Stefan Monnier
2013-07-22 16:33   ` Thien-Thi Nguyen
2013-07-22 21:04     ` Stefan Monnier
2013-07-23  4:37       ` Thien-Thi Nguyen [this message]
2013-08-10  2:52         ` Stefan Monnier
2013-08-10 10:08         ` Pascal J. Bourguignon
2013-08-10 16:27           ` Drew Adams

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