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From: Andreas Rottmann <a.rottmann@gmx.at>
To: Daniel Kraft <d@domob.eu>
Cc: Andy Wingo <wingo@pobox.com>, guile-devel <guile-devel@gnu.org>,
	Neil Jerram <neil@ossau.uklinux.net>
Subject: Re: %nil once again
Date: Fri, 17 Jul 2009 16:20:21 +0200	[thread overview]
Message-ID: <87k527v1ay.fsf@delenn.lan> (raw)
In-Reply-To: <4A603E36.7080100@domob.eu> (Daniel Kraft's message of "Fri, 17 Jul 2009 11:02:46 +0200")

Daniel Kraft <d@domob.eu> writes:

> Hi Neil,
>
> Neil Jerram wrote:
>> Daniel Kraft <d@domob.eu> writes:
>>> I think I got the test-suite as well as a basic macro implementation
>>> (the compiler framework is really cool, that was fairly easy to do);
>>> recursive macros do not yet work, but otherwise it looks fine.
>>>
>>> However, I want to tackle quasi-quotes (besides others) now; and in
>>> Elisp %nil is not only #f of Scheme but also the end-of-list marker (I
>>> guess that's why simply using Scheme's #f for %nil does not work).
>>>
>>> I did some experiments, and it seems that Scheme respects it partially:
>>>
>>> scheme@(guile-user)> `(1 2 3 . ,%nil)
>>> (1 2 3)
>>>
>>> (is %nil in Scheme a variable because it needs the unquote?)
>
Yes (although I'd say you need the unquote because you want to access
the variable, not the other way around </nitpick>).

>>
>> Do you mean why don't we just use the symbol nil?  If so, the answer
>> is because in Scheme, (cons 'a 'nil) should be (a . nil), not (a).
>
> No, I mean why '(1 2 3 . %nil) does yield (1 2 3 . %nil) while `(1 2 3
> . ,%nil) gives the expected (1 2 3).  But that does not matter much
> besides astonishing me, as this is only something related to the
> Scheme implementation of %nil, I guess.
>
The *symbol* '%nil has absolutely no special status in Scheme. It just
happens that Guile provides (in the default environment) a value bound
as %nil that has special properties.

Regards, Rotty
-- 
Andreas Rottmann -- <http://rotty.yi.org/>




  reply	other threads:[~2009-07-17 14:20 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-07-16 13:47 %nil once again Daniel Kraft
2009-07-17  7:59 ` Neil Jerram
2009-07-17  9:02   ` Daniel Kraft
2009-07-17 14:20     ` Andreas Rottmann [this message]
2009-07-19 18:28     ` Neil Jerram
2009-07-19 19:44       ` Daniel Kraft
2009-07-19 20:10         ` Neil Jerram
2009-07-20  3:33           ` Ken Raeburn
2009-07-20  8:12             ` Daniel Kraft
2009-07-20  9:15               ` Ken Raeburn
2009-07-23 22:18             ` Andy Wingo
2009-07-20 18:17 ` Clinton Ebadi
2009-07-30 21:38   ` Neil Jerram
2009-07-31  5:03     ` Daniel Kraft
2009-07-23 20:35 ` Andy Wingo
2009-07-24  6:20   ` Daniel Kraft
2009-07-30 21:50   ` Neil Jerram
2009-07-31  5:05     ` Daniel Kraft

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