Data::Grove::Visitor

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



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

SYNOPSIS
	use Data::Grove::Visitor;

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

DESCRIPTION
       Data::Grove::Visitor adds visitor methods (callbacks) to Data::Grove
       objects.	 A ‘‘visitor’’ is a class (a package) you write that has
       methods (subs) corresponding to the objects in the classes being vis-
       ited.  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 vis-
       itor 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 con-
       tents 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.

       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.

RESERVED NAMES
       The hash keys ‘"Contents"’ and ‘"Name"’ are used to indicate objects
       with children (for ‘"children_accept"’) and named objects (for
       ‘"accept_name"’).

NOTES
       These are random ideas that haven’t been implemented yet:

       ·   Several objects fall into subclasses, or you may want to be able
	   to subclass a visited object and still be able to tell the differ-
	   ence.  In SGML::Grove I had used the package name in the callback
	   (‘"visit_SGML_Element"’) instead of a generic name (‘"visit_ele-
	   ment"’).  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), Data::Grove

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



perl v5.8.5			  2000-02-22	      Data::Grove::Visitor(3)