class Visitor(object):
	def _visit(self, node, prepend, *args):
		prepend = prepend + "_"
		meth = None
		for cls in node.__class__.__mro__:
			meth_name = prepend + cls.__name__
			meth = getattr(self, meth_name, None)
			if meth:
				break

		if not meth:
			meth = self.generic_visit
		return meth(node, *args)
	
	def visit(self, node, *args):
		self._visit(node, "visit", *args)
	
	def enter(self, node, *args):
		self._visit(node, "enter", *args)
		
	def exit(self, node, *args):
		self._visit(node, "exit", *args)

	def generic_visit(self, node):
		#print 'generic_visit '+node.__class__.__name__
		pass
		
class Visitable(object):
	def accept(self, visitor):
		visitor.visit(self)