1# Copyright (c) 2012 The Chromium Authors. All rights reserved.
2# Use of this source code is governed by a BSD-style license that can be
3# found in the LICENSE file.
4
5""" Visitor Object for traversing AST """
6
7#
8# IDLVisitor
9#
10# The IDLVisitor class will traverse an AST truncating portions of the tree
11# when 'VisitFilter' returns false.  After the filter returns true, for each
12# node, the visitor will call the 'Arrive' member passing in the node and
13# and generic data object from the parent call.  The returned value is then
14# passed to all children who's results are aggregated into a list.  The child
15# results along with the original Arrive result are passed to the Depart
16# function which returns the final result of the Visit.  By default this is
17# the exact value that was return from the original arrive.
18#
19
20class IDLVisitor(object):
21  def __init__(self):
22    pass
23
24  # Return TRUE if the node should be visited
25  def VisitFilter(self, node, data):
26    return True
27
28  def Visit(self, node, data):
29    if not self.VisitFilter(node, data): return None
30
31    childdata = []
32    newdata = self.Arrive(node, data)
33    for child in node.GetChildren():
34      ret = self.Visit(child, newdata)
35      if ret is not None:
36        childdata.append(ret)
37    return self.Depart(node, newdata, childdata)
38
39  def Arrive(self, node, data):
40    __pychecker__ = 'unusednames=node'
41    return data
42
43  def Depart(self, node, data, childdata):
44    __pychecker__ = 'unusednames=node,childdata'
45    return data
46