Data::Grove::Visitor(3pm)
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:
- 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 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>