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Re: empty syntax objects

From: Andy Wingo
Subject: Re: empty syntax objects
Date: Tue, 20 Oct 2009 21:22:32 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.92 (gnu/linux)

Hi Daniel,

On Tue 20 Oct 2009 04:44, Julian Graham <address@hidden> writes:

> (syntax-case x ()
>   ((foo . rest)
>    (datum->syntax #'rest 'foo)))
> get an error if `foo' is expanded without anything to bind to
> `rest':

I downloaded Petite Chez Scheme today and tried this out. I also got an
error. I suspect you would get an error with ikarus or other
psyntax-using implementations as well.

> What's the right thing to do here?  Do you just have to be careful
> with what you do with pattern variables that might end up getting
> bound to no arguments?  R6RS isn't totally clear on the topic, but,
> for what it's worth, the same code seems to work in MzScheme.

I think for now the story would just be to be careful, unless you are in
possession of a +12 Cloak of Psyntax Hack :)


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