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Re: Transitive closure for XPath
- From: Joe English <email@example.com>
- To: firstname.lastname@example.org
- Date: Thu, 19 Apr 2001 10:06:48 -0700
Christian Nentwich wrote:
> something I really lose sleep over is the lack of a transitive closure
> function in XPath. [...]
> Would you please comment on a little proposal I have written - includes
> an implementation of the operator for Xalan as a freebie:
This is indeed a very useful feature.
The proposal as described slightly breaks the XPath evaluation
model though: the second argument to 'closure(node-set,node-set)'
has Algol-style call-by-name semantics. That is, it's not really
a node-set but rather an XPath expression or "thunk" which
is re-evaluated with a different context multiple times.
I think this calls for new syntax, either a new keyword or operator.
Postfix '*' might be suitable -
in your example would be written:
On the other hand this plays merry hell with the XPath grammar,
so maybe not...
> Just imagine what this operator could do for *your* family tree XSLT
Not to mention Schematron! A closure operator is all that's
missing to give XPath the full power of ("caterpilar-") regular