An improved ?? construct is part of the public API now. It can be used to
attach predicates to node tests:
xmlNode / 'foo' / ('bar' ?? 10).
or to filter result node sets like this:
(xmlNode / 'foo' / 'bar') ?? 10.
xmlNode / 'foo' / 'bar' ?? 10. "same because of precedence"
The first is equivalent to this:
'foo/bar[10]' asXPath in: xmlNode.
The others are equivalent to this:
'(foo/bar)[10]' asXPath in: xmlNode.
Block predicates take the context node, position, and size as optional (cull:)
arguments. Multiple predicates are done by giving ?? an Array argument or
chaining ?? sends like this:
xmlNode / 'foo' / ('bar' ?? [:each | each includesAttribute: 'name'] ??
1).
Number predicates are faster than blocks and an initial number predicate
attached to a node test (like in the first example) optimizes the node test by
limiting the number of matching nodes it enumerates.
> Sent: Saturday, September 03, 2016 at 11:08 AM
> From: PBKResearch <pe...@pbkresearch.co.uk>
> To: "'Any question about pharo is welcome'" <pharo-users@lists.pharo.org>
> Subject: Re: [Pharo-users] Coding XPath as Smalltalk
>
> Hi Monty
>
> Just to say that I have obtained the Moose 6.0 image (Pharo5.0 Latest update:
> #50761) and installed the XMLHTMLParser, and I seem able to reproduce the
> nucleus of the results I had from my old image. Some of my old XPath strings
> do not work (e.g. it did not recognise [1]), but I have worked my way round
> that, and I should soon have worked out the new syntax. Thanks for your
> suggestions for the variable case; I can now see the way ahead for that.
> Thanks for all the help.
>
> @stef
>
> I have loaded the same version of TextLint as I had in the previous image. It
> was accepted with no problems. I have tested it for the limited uses I make
> of it (just the parsers, not the rules) and everything seems OK. So now I am
> upgraded to Pharo 5, so far with no problems!
>
> Peter Kenny
>
> -----Original Message-----
> From: Pharo-users [mailto:pharo-users-boun...@lists.pharo.org] On Behalf Of
> monty
> Sent: 03 September 2016 13:00
> To: pharo-users@lists.pharo.org
> Subject: Re: [Pharo-users] Coding XPath as Smalltalk
>
>
>
> > Sent: Saturday, September 03, 2016 at 5:30 AM
> > From: PBKResearch <pe...@pbkresearch.co.uk>
> > To: "'Any question about pharo is welcome'" <pharo-users@lists.pharo.org>
> > Subject: Re: [Pharo-users] Coding XPath as Smalltalk
> >
> > Hi Monty
> >
> > Many thanks. I have picked up a project that I had not worked on for a
> > while, which explains why I am using an old image. I shall try the latest
> > Moose image, as you suggest. My only anxiety is that I need to be able to
> > use a rather ancient package called TextLint, and I do not know whether it
> > will load OK in a new Pharo. If not, I shall try to update my existing
> > image.
>
> If you'd looked at CI job, you'd see that XPath builds on Pharo 5 through 3
> (but should work back to 1.4). You can always start fresh with a clean, old
> image from http://files.pharo.org/image/ or the Moose website if TextLint
> doesn't work anymore.
>
> > With the latest XPath, will it be clear how to use the binary syntax to
> > carry out node tests like the example of '//div[@id=''catlinks'']//' that I
> > cited below? The case I am interested in is where the actual identifier
> > ('catlinks' in this case) is a variable rather than a constant. It would be
> > possible to do it in standard XPath by assembling the XPath string with a
> > variable component, but it might be more convenient in the binary syntax.
> >
>
> You could do this:
> ((doc // 'div') select: [:each | (each attributeAt: 'id') = catlinks]) //
> 'li' // 'text()'
>
> where "catlinks" is a var. Or you could use xPath:context: with an XPath var
> that you dynamically bind using custom contexts:
> doc
> xPath: '//div[@id=$catlinks]//li//text()'
> context: (XPathContext variables: {'catlinks' -> catlinks})
>
> The advantage over this:
> doc xPath: '//div[@id=''', catlinks, ''']//li//text()'
>
> is that the xPath: expression string is the same each time, so it's only
> compiled once, the first time, and cached for later uses (inspect 'XPath
> compiledXPathCache') instead of being compiled each time the xPath:
> expression string arg changes.
>
> > Many thanks for your help.
> >
> > Peter Kenny
> >
> > -----Original Message-----
> > From: Pharo-users [mailto:pharo-users-boun...@lists.pharo.org] On Behalf Of
> > monty
> > Sent: 03 September 2016 06:54
> > To: pharo-users@lists.pharo.org
> > Subject: Re: [Pharo-users] Coding XPath as Smalltalk
> >
> > Peter, you're using an ancient version with bugs that were fixed last fall.
> > The newest version has more tests and correct behavior (checked against a
> > reference implementation). Just download a new Moose image and you'll get
> > it, along with an up to date XMLParser. (But if you insist on upgrading in
> > your old image, run "XPath initialize" after)
> >
> > The binary syntax (there are keyword equivalents now) officially only
> > supports XPath axis selectors like #/ and #// that take node test arguments
> > where the node tests can be name tests like 'name,' '*', 'prefix:*' or type
> > tests like 'text()', 'comment()', 'element(name)'.
> >
> > Filters aren't officially supported with that syntax, but you can always
> > use select: on the result. ?? was removed, but I might add it back as
> > shorthand. Filters are implemented differently now.
> >
> > > From: PBKResearch <pe...@pbkresearch.co.uk>
> > > To: pharo-users@lists.pharo.org
> > > Subject: [Pharo-users] Coding XPath as Smalltalk
> > >
> > > Hello
> > >
> > > I am using XPath as a way of dissecting web pages, especially from
> > > Wiktionary. Generally I get good results, but I could get useful extra
> > > flexibility by using the binary Smalltalk operators to represent XPath,
> > > as mentioned at the end of the class comment for XPath. However, the
> > > description there is very terse, and I am having difficulty seeing how to
> > > include more complex expressions, especially attribute tests. I have put
> > > some of my XPath expressions through the XPath compiler and looked at the
> > > output, and out of that I have found expressions which work but look very
> > > clumsy. As an example, I have used the fragment:
> > >
> > > document xPath: '//div[@id=''catlinks'']//li//text()'
> > >
> > > and found that an equivalent is:
> > >
> > > document //'div' ?? [:node :x :y|(node attributeAt: 'id') =
> > > 'catlinks']//'li'//[:n| n isStringNode]].
> > > (I had to put two dummy arguments in the three-argument block to get it
> > > to work.)
> > >
> > > Is there a more extensive explanation of the use of these binary
> > > operators? If not, could some kind person show me the most concise
> > > translation of the sample XPath above, to give me a start in working out
> > > more complex cases?
> > >
> > > Many thanks for any help.
> > >
> > > Peter Kenny
> >
> >
> >
>
>
>
