6 files changed, 102 insertions, 0 deletions
diff --git a/lib/psych.rb b/lib/psych.rb
index 9d136d5..d39a284 100644
--- a/lib/psych.rb
+++ b/lib/psych.rb
@@ -1,4 +1,9 @@
+require 'psych/nodes/node'
+require 'psych/nodes/stream'
+require 'psych/nodes/document'
+
 require 'psych/handler'
+require 'psych/tree_builder'
 require 'psych/parser'
 require 'psych/psych'
 
diff --git a/lib/psych/nodes/document.rb b/lib/psych/nodes/document.rb
new file mode 100644
index 0000000..8dc0a13
--- /dev/null
+++ b/lib/psych/nodes/document.rb
@@ -0,0 +1,12 @@
+module Psych
+  module Nodes
+    class Document < Psych::Nodes::Node
+      def initialize version, tag_directives, implicit
+        super()
+        @version        = version
+        @tag_directives = tag_directives
+        @implicit       = implicit
+      end
+    end
+  end
+end
diff --git a/lib/psych/nodes/node.rb b/lib/psych/nodes/node.rb
new file mode 100644
index 0000000..cb8f632
--- /dev/null
+++ b/lib/psych/nodes/node.rb
@@ -0,0 +1,14 @@
+module Psych
+  module Nodes
+    ###
+    # The base class for any Node in a YAML parse tree.  This class should
+    # never be instantiated.
+    class Node
+      attr_reader :children
+
+      def initialize
+        @children = []
+      end
+    end
+  end
+end
diff --git a/lib/psych/nodes/stream.rb b/lib/psych/nodes/stream.rb
new file mode 100644
index 0000000..911bea8
--- /dev/null
+++ b/lib/psych/nodes/stream.rb
@@ -0,0 +1,14 @@
+module Psych
+  module Nodes
+    ###
+    # Represents a YAML stream.  This is the root node for any YAML parse
+    # tree.
+    class Stream < Psych::Nodes::Node
+      attr_reader :encoding
+      def initialize encoding
+        super()
+        @encoding = encoding
+      end
+    end
+  end
+end
diff --git a/lib/psych/tree_builder.rb b/lib/psych/tree_builder.rb
new file mode 100644
index 0000000..3f11fd9
--- /dev/null
+++ b/lib/psych/tree_builder.rb
@@ -0,0 +1,29 @@
+require 'psych/handler'
+
+module Psych
+  ###
+  # This class builds an in-memory parse tree tree that represents a YAML
+  # document.
+  #
+  # See Psych::Handler for documentation on the event methods used in this
+  # class.
+  class TreeBuilder < Psych::Handler
+    def initialize
+      @stack = []
+    end
+
+    def root
+      @stack.first
+    end
+
+    def start_stream encoding
+      @stack.push Nodes::Stream.new encoding
+    end
+
+    def start_document version = [], tag_directives = [], implicit = true
+      doc = Nodes::Document.new version, tag_directives, implicit
+      @stack.last.children << doc
+      @stack.push doc
+    end
+  end
+end
diff --git a/test/psych/test_tree_builder.rb b/test/psych/test_tree_builder.rb
new file mode 100644
index 0000000..62998db
--- /dev/null
+++ b/test/psych/test_tree_builder.rb
@@ -0,0 +1,28 @@
+require 'helper'
+
+module Psych
+  class TestTreeBuilder < Test::Unit::TestCase
+    def setup
+      @parser = Psych::Parser.new TreeBuilder.new
+      @parser.parse(<<-eoyml)
+%YAML 1.1
+---
+- foo
+- {
+  bar : &A !!str baz,
+  boo : *A
+}
+      eoyml
+      @tree = @parser.handler.root
+    end
+
+    def test_stream
+      assert_instance_of Nodes::Stream, @tree
+    end
+
+    def test_documents
+      assert_equal 1, @tree.children.length
+      assert_instance_of Nodes::Document, @tree.children.first
+    end
+  end
+end