Content-Type: multipart/signed; boundary=Apple-Mail-4-657483046; micalg=sha1; protocol="application/pkcs7-signature"
Mime-Version: 1.0 (Apple Message framework v935.3)
References: <4A7921CF.5020803@morningstar2.co.uk>                              
            <4A7A1505.4040604@residenset.net>                      
            <DB76B425-0A88-43B4-9CF0-B92FAF159E37@gmail.com>           
            <4A7A726F.3080006@morningstar2.co.uk>           
            <4A7A857F.4010400@morningstar2.co.uk>
            <D4298EE7-4070-4D91-B364-A69CEF48428F@gmail.com>
            <4A7A906B.6080709@morningstar2.co.uk>
Message-ID:  <913BFFC3-4041-4426-9FCB-49E95C7C2541@gmail.com>
Date:         Thu, 6 Aug 2009 18:03:42 +0930
Reply-To: Mailing list for the LaTeX3 project
              <LATEX-L@LISTSERV.UNI-HEIDELBERG.DE>
Sender: Mailing list for the LaTeX3 project <LATEX-L@LISTSERV.UNI-HEIDELBERG.DE>
From: Will Robertson <wspr81@GMAIL.COM>
Subject: Re: xparse
To: LATEX-L@LISTSERV.UNI-HEIDELBERG.DE
In-Reply-To:  <4A7A906B.6080709@morningstar2.co.uk>
Precedence: list
Status: R

--Apple-Mail-4-657483046
Content-Type: text/plain;
	charset=US-ASCII;
	format=flowed;
	delsp=yes
Content-Transfer-Encoding: 7bit

On 06/08/2009, at 5:42 PM, Joseph Wright wrote:

>> I like this way of doing coordinates. Could 'd{}{-default-}' be
>> shoe-horned into this syntax as well? I suppose that would mean
>> completely re-writing the parser. But then we wouldn't need another
>> letter for my feature of limited value.
>
> I thought about this.  There is an issue, though.  For a standard
> delimited argument, the two "ends" are arbitrary: [) will work as well
> as [].  You can easily pick up:
>
> d{ ...
>
> for the opening-group token, but in this case you have to have a  
> closing
> group token as the closing token (both for d{} and for gathering the
> argument).  So d[]{default} and d{}{default} are subtly but  
> importantly
> different.  I'm not opposed, though:
>
> "d{}{<default>} can be used to include an optional argument surrounded
> by braces.  Note that in this case the closing token *must* be a
> close-group token (usually `}')."

Yep, sounds good.
So, to perhaps summarise:

m M - mandatory braced argument
d D <x><y> - optional delimited argument; picks up material between  
<x> and <y>. Can be used for {}, (), etc. Can be followed by a default  
value to use.
o O - shorthand for d[]
t <x> - lookahead for optional <x>
s   - shorthand for t*
l L - everything before the next brace (not often used, but sometimes  
useful)

No longer:

c<x><y> - as d() but mandatory; can perform the check manually (only a  
small processing overhead?).
p - shorthand for d(); drop this to keep things simple.

* * *

Open issues:

  - Do we want to support something like 'd{[[}{]]}{default}' to allow  
\foo[[bar]] ? (I'd say no.)
  - Do we want to support something analogous to
        \def\foo #1\endfoo{...#1...}
    Consider active quotes, and macros like '\<...>'
    Maybe this is as important to support as 'l'.
    Could use the letter 'u{<token>}' for "until".

Any thoughts?

Will


--Apple-Mail-4-657483046
Content-Disposition: attachment;
	filename=smime.p7s
Content-Type: application/pkcs7-signature;
	name=smime.p7s
Content-Transfer-Encoding: base64
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--Apple-Mail-4-657483046--