[plexippus-xpath-devel] do-node-set woes

[Peter Stiernström]

Thank you Ivan and David,

You are of course both correct that the error was in my xpath-fu and
not plexippus. I am thouroughly ashamed of this newbie question and
will make sure to inspect my expressions more vigirously before
posting again!

/Peter

On Tue, May 26, 2009 at 03:12:28PM +0400, Ivan Shvedunov wrote:
> Hello,
> 
> 2009/5/26 Peter Stiernström <peter at stiernstrom.se>:
> > Hello xpath developers,
> >
> > I am trying to use plexippus-xpath and have hit a wall concerning the
> > use of evaluate together with do-node-set. I am under the impression
> > that the the second argument given to evaluate should be a document or
> > a node. What I am trying to accomplish is to write a function that
> > runs various xpath expressions on a subset of the document like so:
> >
> > (let ((doc (cxml:parse "<a><b><c><d>1</d></c><c><d>2</d></c><c><d>3</d></c></b></a>"
> >                       (cxml-dom:make-dom-builder))))
> >  (xpath:do-node-set (n (xpath:evaluate "//c" doc))
> >    (format t "~d~%" (xpath:number-value (xpath:evaluate "//d" n)))))
> >
> > I would like to have this print:
> > 1
> > 2
> > 3
> >
> > But instead it always prints:
> > 1
> > 1
> > 1
> 
> It should be noted that //c in the last expression (same as
> /descendant-or-self::node()/c) works
> relative to the root node of the document and not the context node,
> thus you get 1 every time.
> Perhaps what you want is descendant::d as the last expression (.//d
> will also work in this
> concrete case though).
> 
> (let ((doc (cxml:parse
> "<a><b><c><d>1</d></c><c><d>2</d></c><c><d>3</d></c></b></a>"
>                        (cxml-dom:make-dom-builder))))
>   (xpath:do-node-set (n (xpath:evaluate "//c" doc))
>                      (format t "~d~%" (xpath:number-value
> (xpath:evaluate "descendant::d" n)))))
> 
> (I'd write the FORMAT form as (format t "~d~%" (xpath:evaluate
> "number(descendant::d)" n)) though).
> 
> > If I instead change my code to this:
> >
> > (let ((doc (cxml:parse "<a><b><c><d>1</d></c><c><d>2</d></c><c><d>3</d></c></b></a>"
> >                       (cxml-dom:make-dom-builder))))
> >  (xpath:do-node-set (n (xpath:evaluate "//c" doc))
> >    (format t "~a~%" (dom:map-document (cxml:make-string-sink) n))))
> >
> > It prints (as expected):
> >
> > <?xml version="1.0" encoding="UTF-8"?>
> > <d>1</d>
> > <?xml version="1.0" encoding="UTF-8"?>
> > <d>2</d>
> > <?xml version="1.0" encoding="UTF-8"?>
> > <d>3</d>
> >
> > So my conclusion is that somehow my use of evaluate does not work
> > according to my expectations, if those are valid or not is something I
> > leave up to you to decide :)
> >
> > Now please strike me with your clue sticks!
> >
> 
> Well, in this case the second expression is absent, so there's no problem :)
> 
> Ivan.
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