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 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.

       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 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), Data::Grove

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