[plt-scheme] XML ease of use

From: Eddie Sullivan (eddieSull at hotmail.com)
Date: Tue Aug 4 12:22:34 EDT 2009

Thanks for the reply, Jay.
I guess your point is that since XML is strict about types, the library must 
be as well. That does make sense.

I think I'll try Robby's suggested approach of converting xml to xexpr, 
processing, then converting back to xml. Is there any potential data loss I 
need to worry about with that approach?

(BTW, I hope the tone of my original email wasn't too grumpy. It's still 
early in the morning here.)

-Eddie Sullivan

----- Original Message ----- 
From: "Jay McCarthy" <jay.mccarthy at gmail.com>
To: "Eddie Sullivan" <eddieSull at hotmail.com>
Cc: <plt-scheme at list.cs.brown.edu>
Sent: Tuesday, August 04, 2009 9:10 AM
Subject: Re: [plt-scheme] XML ease of use

> Hi Eddie,
> On Tue, Aug 4, 2009 at 9:51 AM, Eddie Sullivan<eddieSull at hotmail.com> 
> wrote:
>> Hello.
>> I've lately been having all kinds of frustrations making things work with
>> the XML library. The biggest hurdle seems to be keeping track of all the
>> types. We have "document" and "element" and "content" and "prolog" and
>> "entity" and "pcdata" and so on and so forth. Every function seems to 
>> accept
>> a different type.
> The contracts in the XML library are very strict and specific to
> ensure that only correct XML (modulo the cdata escape valve) is
> generated. Each function accepts a different type because that is what
> they must accept. Perhaps what you'd like is some stratum of
> write/read-xml and xml->xexpr variants that deal with only the
> subtypes of document and element. These are implemented in the collect
> and could conceivably be exposed. Is that what you mean?
>> I think it would be helpful if there were some kind of abstract 
>> super-type
>> for at least some of these things. Something similar to what the 
>> "content/c"
>> contract checks for would be ideal, so that all those items could be 
>> treated
>> the same until we wanted to differentiate them. Except I would think that
>> "pcdata" and the like would be subtypes of "element."
> It sounds like you are saying that you'd like dispatching inside of
> the XML collect rather than selection outside of the XML collect. This
> is an imaginable supplement and I would consider including it in the
> collect, but I don't think the core library should change in that
> error-prone direction. With this approach, when you give the wrong
> type it is an error, in that regime you would get different behavior
> because a different dispatch would be invoked.
>> One other thing that bites me every time is that the "content" field of 
>> the
>> "element" structure is actually specified by the contract (listof
>> content/c). Either the name is wrong or the contract is.
> Unfortunately 'content' can be plural or singular in English. The
> element has content, that content is made up of a list of content
> item. A content item's contract is content/c and the element contains
> a number of these. Perhaps if it were easy to change from content to
> contents and not break too much code, I'd consider a change.
>> I don't know if self-referential contracts are possible, but it would be
>> nice if content/c was really something like (or/c
>> (current-definition-of-content/c) (listof content/c)). That's only one
>> possible solution, though.
> That would be incorrect in other cases, such as write-xml/content and
> xexpr->xml.
>> The reason I don't like getting this (listof content/c) is that there is 
>> not
>> much useful I can do with it. Since it doesn't satisfy content/c, I can't
>> pass it to xml->xexpr or write-xml/content. Since it's not a document, I
>> can't pass it to write-xml. I suppose I could do (apply string-append 
>> (map
>> write-xml thing)), but that seems more involved than it has to be. If I
>> could treat (listof content/c) the same as content/c that would go a long
>> way towards making things easier.
> You could write:
> (define (write-xml/contents cs)
> (for-each write-xml/content cs))
> and use the same with-output-to-string that you would normally.
> This is the sort of thing that a patch might be reasonable.
>> A form like "xml-match" would be very helpful, too, to avoid having to 
>> delve
>> into the internals of the different xml structures.
> What would this do? Would it be an XQuery?
>> I think PLT Scheme's XML capabilities are very close to being the best 
>> thing
>> out there, so I hope you take these as constructive suggestions.
>> Thanks!
>> -Eddie Sullivan
> Thank _you_.
> Jay
> -- 
> Jay McCarthy <jay at cs.byu.edu>
> Assistant Professor / Brigham Young University
> http://teammccarthy.org/jay
> "The glory of God is Intelligence" - D&C 93

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