On Fri, 2004-12-31 at 15:27 +1100, Dimitre Novatchev wrote:
> One has to realize that error raising/handling in a functional language is 
> essentially nondeterministic and much more challenging as such. XPath 1.0 
> compatibility would also be very problematic, as there's almost no such 
> thing as raising an error in XPath 1.0.

I don't understand.  There are some errors defined for XPath 1.0, e.g.
using a namespace prefix that is not declared in the context.

Side note: the example in Mike Kay's saxon:try extension seems to
intimate that 1 div 0 is an error, which it isn't: it's just Inf.

The spec does not say how implementations should deal with such errors
(correctly so), but there are errors defined.


> More on implementing exceptions in a functional language can be found in the 
> classic work of Simon-Peyton Jones "Tackling the awkward squad: monadic 
> input/output, concurrency, exceptions, and foreign-language calls in 
> Haskell", at 
> http://research.microsoft.com/Users/simonpj/papers/marktoberdorf/
> 
> While I actually made some successful experiments 1 1/2 years ago, it seems 
> too early to expect these in XSLT. My predictions (which are typically 
> optimistic) are for HOF support in XPath/XSLT 3.0 and try/catch-type error 
> handling in XPath/XSLT 4.0.

I appreciate this caution, but I think that providing error handling
declarations, dynamic evaluate and higher-order-functions in XSLT 2.0
would have been much more useful than any of the things that did make it
in.

I find Mike Kay's recounting of the history of the try/catch idea very
interesting as an illustration of how close integration with XQuery
proved detrimental in the development of XSLT and XPath 2.0.


-- 
Uche Ogbuji                                    Fourthought, Inc.
http://uche.ogbuji.net    http://4Suite.org    http://fourthought.com
Use CSS to display XML - http://www.ibm.com/developerworks/edu/x-dw-x-xmlcss-i.html
Full XML Indexes with Gnosis - http://www.xml.com/pub/a/2004/12/08/py-xml.html
Be humble, not imperial (in design) - http://www.adtmag.com/article.asp?id=10286
UBL 1.0 - http://www-106.ibm.com/developerworks/xml/library/x-think28.html
Use Universal Feed Parser to tame RSS - http://www.ibm.com/developerworks/xml/library/x-tipufp.html
Default and error handling in XSLT lookup tables - http://www.ibm.com/developerworks/xml/library/x-tiplook.html
A survey of XML standards - http://www-106.ibm.com/developerworks/xml/library/x-stand4/
The State of Python-XML in 2004 - http://www.xml.com/pub/a/2004/10/13/py-xml.html