use Perl

• Tree Matching? (Score:2, Informative)

  by chromatic (983)

  I just wrote B::SAX yesterday (yes, it fires SAX events based on traversing a compiled Perl optree). Is it possible to run XPath over SAX events?

  Otherwise, I'll have to write a little state machine to find the subtree I'm seeking. That doesn't sound too awful, but the less work, the better.
  • Re:Tree Matching? (Score:2)

    by Matts (1087)

    Yes, see Barrie Slaymaker's XML::Filter::Dispatcher.
    
    Either that or build a DOM (using something like XML::LibXML::SAX::Builder) and go from there.
• yup (Score:3, Informative)

  by wickline (135) on 2003.02.27 7:12 (#17558) Journal

  > Would you use such a module?
  
  I'd love to :)
  
  I can also imagine that it would also be handy to have the module work without having Some::Node's author build in support. This could allow your code to work with modules which were written before your release, and modules that didn't feel like adding yet another feature.

  #!/usr/bin/perl
  use HTML::TreeBuilder;
  use HTML::Element;
  use Class::XPath (
       install_in => 'HTML::Element',
       %the_get_foo_mappings,
  );

  or maybe

  #!/usr/bin/perl
  use HTML::TreeBuilder;
  use Class::XPath;
  my $tree = HTML::TreeBuilder->new();
  my $xp_tree = Class::XPath (
       use_object => $tree,
       %the_get_foo_mappings,
  );

  If get_attr is supposed to return a list of attributes, then you'll probably need a get_attr_value or something too.
  
  On the other hand, if get_attr is expected to take an attribute name and return a value (or undefined if the attribute does not exist) then there may be a problem in situations where the underlying object may allow for undef to be a reasonable value for an attribute. For example, if someone wanted to use Class::XPath to traverse a messy perl data structure, some of the values might well be undef. ...or maybe get_attr could work like CGI::param in the sense of returning a list of attributes when called without any args, and returning the value for a given attribute when passed that attribute.
  
  I'm curious: how does XPATH handle meta-character escapes? I'm imagining the case of applying it to some representation of a CSS document. A selector's value may well contain a whole host of XPATH-looking syntax. You may want to expose an escape method, or alternate versions of each method (one which escapes the path/attr, one which does not).
  
  In any case, I think the module is a great idea. It seems like a very sensible abstraction that lets XPATH work happen in one place and allows everyone the option of bolting XPATH support onto their project.
  
  -matt

  Reply to This

  • Re:yup (Score:1)

    by dlc (50)

    How about maybe:

      package Foo;
      use base qw(Class::XPath);

    Class::XPath can be designed to be mixed-in to any arbitrary class, and simply provide a match method. Seems much simpler.

    --
    (darren)
    • Re:yup (Score:2)

      by samtregar (2699)

      How does Class::XPath magically know how to operate on the nodes of your tree unless you tell it? Sure, inheritence is an option but I doubt the end result would require any less configuration.

      -sam
      • Re:yup (Score:1)

        by dlc (50)

        I wasn't disgreeing with the need for configuration, just the need usage examples. I was suggesting something more like:

          use base qw(Class::XPath);
        
          sub new {
              my $class = shift;
              my $self = bless { } => $class;
        
              $self->create_matcher(%xpath_stuff);
        
              return $self;
          }

        Though I would suggest that a good default match method would be one that could automatically walk a data structure (i.e., didn't use metho

        --
        (darren)