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variable binding in XPath was: Comments on XPath (30th April)

From: David Carlisle <davidc@nag.co.uk>
Date: Wed, 22 May 2002 09:50:15 +0100
Message-Id: <200205220850.JAA14045@penguin.nag.co.uk>
To: Michael.Kay@softwareag.com
CC: public-qt-comments@w3.org
me>   The fact that for expressions mean that it possible in XPath to bind
me>   variables to items but not to sequences is a very strange state of
me>   affairs.

mike> You think we should allow "let" in XPath?

On reflection, I think yes.


mike>* provide a simple (context-based) FOR expression only
mike>* provide a full FOR expression with range variables
mike>* provide both

A suggestion.

* Remove the "full" for from Xpath.
* Provide a simpler context based for, either something like

"foreach" Expr "return" Expr
or something more symbolic, Xpath-like  syntax, I'd quite like

 Expr => Expr  

(with => taking the same precedence as /, and doing a similar job but
not restricted to node sequences and not applying doc-order to the
result) I know => is currently being used for something else....

* Provide let (with the current XQuery syntax)


The advantages of this over the current situation are 

a) that simple mappings over sequences (by far the majority case in
Xpath use, I would expect) are simpler, not requiring explicit variables
at all.

b) There is more functionality for more complicated cases as you can
bind any value to a variable, not just non-sequence items. For nested
for constructs where you need variables to save the context you'd do the
equivalent of what you do already for xsl:for-each, something like

foreach $lista return
  let $a . in
     foreach $listb
        return my:f(.,$a)
   

David

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Received on Wednesday, 22 May 2002 04:50:41 GMT

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