From peter at stiernstrom.se  Tue May 26 11:01:00 2009
From: peter at stiernstrom.se (Peter =?iso-8859-1?Q?Stiernstr=F6m?=)
Date: Tue, 26 May 2009 13:01:00 +0200
Subject: [plexippus-xpath-devel] do-node-set woes
Message-ID: <20090526110100.GA27718@peter.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

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!

/ Peter
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From david at lichteblau.com  Tue May 26 11:05:08 2009
From: david at lichteblau.com (David Lichteblau)
Date: Tue, 26 May 2009 13:05:08 +0200
Subject: [plexippus-xpath-devel] do-node-set woes
In-Reply-To: <20090526110100.GA27718@peter.stiernstrom.se>
References: <20090526110100.GA27718@peter.stiernstrom.se>
Message-ID: <20090526110508.GB4563@radon>

Quoting Peter Stiernstr?m (peter at stiernstrom.se):
>   (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

Use ".//d" rather than "//d".  The latter doesn't start at N, it starts
at the root of the document, ignoring the context node N.


d.



From ivan4th at gmail.com  Tue May 26 11:12:28 2009
From: ivan4th at gmail.com (Ivan Shvedunov)
Date: Tue, 26 May 2009 15:12:28 +0400
Subject: [plexippus-xpath-devel] do-node-set woes
In-Reply-To: <20090526110100.GA27718@peter.stiernstrom.se>
References: <20090526110100.GA27718@peter.stiernstrom.se>
Message-ID: <4d93c5bf0905260412w49a5d86cracef6dcc67b775bc@mail.gmail.com>

Hello,

2009/5/26 Peter Stiernstr?m <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.



From peter at stiernstrom.se  Tue May 26 11:42:00 2009
From: peter at stiernstrom.se (Peter =?iso-8859-1?Q?Stiernstr=F6m?=)
Date: Tue, 26 May 2009 13:42:00 +0200
Subject: [plexippus-xpath-devel] do-node-set woes
In-Reply-To: <4d93c5bf0905260412w49a5d86cracef6dcc67b775bc@mail.gmail.com>
References: <20090526110100.GA27718@peter.stiernstrom.se>
	<4d93c5bf0905260412w49a5d86cracef6dcc67b775bc@mail.gmail.com>
Message-ID: <20090526114200.GA29283@peter.stiernstrom.se>

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 Stiernstr?m <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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