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Data::Grove::Visitor(3)        User Contributed Perl Documentation	  Data::Grove::Visitor(3)

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

	use Data::Grove::Visitor;

	@results = $object->accept ($visitor, ...);
	@results = $object->accept_name ($visitor, ...);
	@results = $object->children_accept ($visitor, ...);
	@results = $object->children_accept_name ($visitor, ...);

       Data::Grove::Visitor adds visitor methods (callbacks) to Data::Grove objects.  A ``visi-
       tor'' is a class (a package) you write 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 ele-
       ment object calls you back with `"visit_name_NAME"' where NAME is the tag name of the ele-
       ment, 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"'

       `"children_accept"' calls `"accept"' on each of the children of the element.  This is gen-
       erally 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.  `"chil-
       dren_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.

       Refer to the documentation of the classes you are visiting (XML::Grove, etc.) for the type
       names (`"element"', `"document"', etc.) of the objects it implements.

       The hash keys `"Contents"' and `"Name"' are used to indicate objects with children (for
       `"children_accept"') and named objects (for `"accept_name"').

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

       o   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 pack-
	   age 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.

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

       perl(1), Data::Grove

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

perl v5.8.0				    2000-02-22			  Data::Grove::Visitor(3)
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