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Re: Double unquote/unquote-splicing
From: |
Stefan Monnier |
Subject: |
Re: Double unquote/unquote-splicing |
Date: |
Mon, 04 Nov 2013 12:27:00 -0500 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux) |
> (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
- Double unquote/unquote-splicing, Nathan Trapuzzano, 2013/11/04
- Re: Double unquote/unquote-splicing,
Stefan Monnier <=
- Re: Double unquote/unquote-splicing, Nathan Trapuzzano, 2013/11/04
- Re: Double unquote/unquote-splicing, Nathan Trapuzzano, 2013/11/04
- Re: Double unquote/unquote-splicing, Stefan Monnier, 2013/11/04
- RE: Double unquote/unquote-splicing, Drew Adams, 2013/11/04
- Re: Double unquote/unquote-splicing, Nathan Trapuzzano, 2013/11/04
- Re: Double unquote/unquote-splicing, Stefan Monnier, 2013/11/04
- Re: Double unquote/unquote-splicing, Nathan Trapuzzano, 2013/11/05
- Re: Double unquote/unquote-splicing, Stefan Monnier, 2013/11/05
- Re: Double unquote/unquote-splicing, Stephen J. Turnbull, 2013/11/04
- Re: Double unquote/unquote-splicing, Nathan Trapuzzano, 2013/11/05