1#!/usr/bin/ruby
2# encoding: utf-8
3
4=begin LICENSE
5
6[The "BSD licence"]
7Copyright (c) 2009-2010 Kyle Yetter
8All rights reserved.
9
10Redistribution and use in source and binary forms, with or without
11modification, are permitted provided that the following conditions
12are met:
13
14 1. Redistributions of source code must retain the above copyright
15    notice, this list of conditions and the following disclaimer.
16 2. Redistributions in binary form must reproduce the above copyright
17    notice, this list of conditions and the following disclaimer in the
18    documentation and/or other materials provided with the distribution.
19 3. The name of the author may not be used to endorse or promote products
20    derived from this software without specific prior written permission.
21
22THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
23IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
24OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
25IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
26INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
27NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
28DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
29THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
30(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
31THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
32
33=end
34
35module ANTLR3
36module AST
37
38=begin rdoc ANTLR3::AST::Visitor
39
40AST::Visitor is an extra utility class for working with tree objects. Visitor
41objects are similar to plain vanilla iterators, but provide two action hooks,
42instead a standard single iteration block. The <tt>visit(tree)</tt> method walks
43through each node of the tree (top-down left-to-right). If +pre_action+ is
44defined, a node is yielded to the block when it has been initially entered. If
45+post_action+ is defined, a node is yielded to the block after all of its
46children have been visited.
47
48=end
49
50class Visitor
51  def initialize( adaptor = nil )
52    @adaptor = adaptor || CommonTreeAdaptor.new()
53    @pre_action = nil
54    @post_action = nil
55    block_given? and yield( self )
56  end
57  
58  def pre_action( &block )
59    block_given? and @pre_action = block
60    return @pre_action
61  end
62  
63  def post_action( &block )
64    block_given? and @post_action = block
65    return @post_action
66  end
67  
68  def visit( tree, pre_action = nil, post_action = nil )
69    flat = @adaptor.flat_list?( tree )
70    before = pre_action || @pre_action
71    after = post_action || @post_action
72    
73    tree = before.call( tree ) unless before.nil? or flat
74    @adaptor.child_count( tree ).times do |index|
75      child = @adaptor.child_of( tree, index )
76      visit( child, pre_action, post_action )
77    end
78    tree = after.call( tree ) unless after.nil? or flat
79    
80    return tree
81  end
82end
83end
84end
85