Re: Extension candidates

Michael Kay wrote:
>>   That brings the question: what would be the type of a 
>> function?  If I am right, it would be a new specialized kind 
>> of item (as nodes are). 
> 
> John Snelson did a lot of work on this (with some input from me). Yes, we
> had function() as a third kind of item, and then we had a type hierarchy so
> that for example function(int)->NCName was a subtype of
> function(int)->string. Obviously it's very open-ended how far you go down
> this route, and when we're doing it as an extension to the language, rather
> than a proposal to extend its core, we need to be less ambitious.

Sorry for disappearing from the discussion - I came down with the 
stomach bug that seems to be going around the UK.

For people's interest, I've posted the proposal I wrote for higher order 
functions in XQuery here:

http://snelson.org.uk/~jpcs/higher-order-functions.html

As Michael says, it might be appropriate for EXSLT to attempt something 
simpler than this proposal - but it will hopefully give people something 
to think about.

> Extension types in Saxon (like the type of the result of saxon:function()),
> are in fact subtypes of xs:anyAtomic rather than being a third kind of item.
> That's largely a matter of implementation convenience, but it simplifies a
> lot of the rules.

I'm interested in why this make things simpler. I would have thought it 
would bring up hard problems of how and whether to allow casting, 
serialization etc.

John

-- 
John Snelson, Oracle Corporation            http://snelson.org.uk/john
Berkeley DB XML:            http://oracle.com/database/berkeley-db/xml
XQilla:                                  http://xqilla.sourceforge.net