[plt-scheme] Unifying xexpr, SXML, and SHTML

From: Matthias Felleisen (matthias at ccs.neu.edu)
Date: Tue Mar 10 08:13:40 EDT 2009

1. Consider using Typed Scheme to formulate the type of XEXPRs you  
want to use.

2. Anything that unifies the various XML things is good.

-- Matthias

On Mar 10, 2009, at 4:19 AM, Neil Van Dyke wrote:

> Any thoughts on this?
> My Scheme libraries for HTML and XML right now use a variation on  
> I'm thinking of moving all my tools to a variation on "xexpr" that  
> is also (or can be) a valid subset of SXML.
> This would let my libraries work better with PLT libraries that use  
> "xexpr" and "xml", while retaining compatibility with the various  
> SXML tools by Oleg Kiselyov and Kirill Lisovsky.
> It would also officially excuse me from having to support the  
> arbitrary list nesting of SXML, which I've found hides programming  
> errors by library users.  (The drawback to eliminating this  
> arbitrary nesting is that some construction of "xexpr" can require  
> large list splicing that would not be necessary in SXML.)
> For portability and human readability, this variation on "xexpr"  
> would be expressed entirely in pairs, symbols, strings, and  
> numbers, *not*
> Just for the sake of discussion, let's call this variation "xepxr2".
> Here are the proposed differences "xexpr2" has relative to "xexpr":
> * An "@" symbol as the first element of an attributes list is  
> permitted but not required.  This is for SXML compatibility.
> * CDATA is represented as a list with the symbol "*CDATA*" as the  
> first element, followed by one of more strings, which,  
> concatenated, are the exact CDATA content, *not* including the XML  
> bracketing syntax.  Some tools may support an "xexpr" "struct"-like  
> "cdata" representation as an alternative, but must accept this list  
> form.
> * Comments are represented as CDATA, except the symbol is "*COMMENT*".
> * XML processing instructions has a specialized form, with the  
> first element being the symbol "*PI*".
> * DOCTYPE has a specialized list form, with the first element being  
> the symbol "*DOCTYPE*".
> There would also be a variation on "xexpr2", which would permit  
> other object types to appear in content and attribute values.  The  
> main purpose of this is to permit absolute URI objects to be  
> embedded in "xexpr2" for last-minute reverse-resolution by HTML  
> writers, for robustness in complicated apps:
> http://www.neilvandyke.org/weblog/2005/01/#2005-01-31
> Source location information might be embedded too, as "struct"-like  
> objects that can be dropped into the list syntax as markers and  
> normally ignored by processing.  I haven't decided on this, but  
> it's something that will be needed sometimes, and we might want to  
> have it in "xexpr2" rather than having a separate representation  
> like PLT's "xml".
> Any thoughts on this appreciated.
> Thanks,
> Neil
> -- 
> http://www.neilvandyke.org/
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