/ 
XML-Grove-0.05
River stage zero No dependents
/ XML::Grove::Visitor

NAME

XML::Grove::Visitor - add visitor/callback methods to XML objects

SYNOPSIS

use XML::Grove::Visitor;

@results = $xml_object->accept ($visitor, ...);
@results = $xml_object->accept_name ($visitor, ...);
@results = $xml_object->children_accept ($visitor, ...);
@results = $xml_object->children_accept_name ($visitor, ...);
@results = $element->attr_accept ($attr, $visitor, ...);

DESCRIPTION

XML::Grove::Visitor adds visitor methods (callbacks) to XML objects and their iterators. A ``visitor'' is a class (a package) that has methods (subs) corresponding to the objects in the classes being visited. You use the visitor methods by creating an instance of your visitor class, and then calling `accept($my_visitor)' on the top-most object you want to visit, that object will in turn call your visitor back with `visit_OBJECT', where OBJECT is the type of object.

There are several forms of `accept'. Simply calling `accept' calls your package back using the object type of the object you are visiting. Calling `accept_name' on an element object calls you back with `visit_name_NAME' where NAME is the tag name of the element, on all other objects it's as if you called `accept'.

All of the forms of `accept' return a concatenated list of the result of all `visit' methods.

`children_accept' calls `accept' on each of the children of the element. This is generally used in element callbacks to recurse down into the element's children, you don't need to get the element's contents and call `accept' on each item. `children_accept_name' does the same but calling `accept_name' on each of the children. `attr_accept' calls `accept' on each of the objects in the named attribute.

If the child object you are visiting is a Perl scalar, you will be called back with `visit_scalar'. The complete list of callbacks defined by XML::Grove::Visitor are:

visit_grove
visit_element
visit_entity
visit_pi
visit_comment
visit_scalar

When using `accept' methods with an iterator, the child objects you get called back with will also be iterators, including `visit_scalar'.

See also the examples `visitor.pl' and `my-html.pl'.

HMM

These are random ideas that haven't been implemented yet:

  • Some people like their subs a little simpler, i.e. drop the `visit_'. In SGML::Grove, tag names were called back with the SGML equivalent, `visit_gi_NAME' (generic identifier). Both of these could possibly be made into options.

  • Several objects fall into subclasses, or you may want to be able to subclass a visited object and still be able to tell the difference. In SGML::Grove I had used the package name in the callback (`visit_SGML_Element') instead of a generic name (`visit_element'). The idea here would be to try calling `visit_PACKAGE' with the most specific class first, then try superclasses, and lastly to try the generic.

AUTHOR

Ken MacLeod, ken@bitsko.slc.ut.us

SEE ALSO

perl(1), XML::Parser(3), XML::Parser::Grove(3).

Extensible Markup Language (XML) <http://www.w3c.org/XML>