public static void CompareNodes(EditorTree editorTree, IAstNode node1, IAstNode node2)
        {
#if ___DEBUG
            Debug.Assert(node1 is RootNode || editorTree.ParseTree.ContainsElement(node1.Key));

            if (!node1.ChildrenInvalidated)
                Debug.Assert(node1.Children.Count == node2.Children.Count);

            Debug.Assert(TextRange.AreEqual(node1.NameRange, node2.NameRange));
            Debug.Assert(node1.Attributes.Count == node2.Attributes.Count);

            Debug.Assert(TextRange.AreEqual(node1.OuterRange, node2.OuterRange));
            Debug.Assert(TextRange.AreEqual(node1.InnerRange, node2.InnerRange));

            Debug.Assert(node1.Start == node2.Start);
            Debug.Assert(node1.End == node2.End);

            if (!node1.ChildrenInvalidated)
            {
                if (node1.Children.Count == node2.Children.Count)
                {
                    for (int i = 0; i < node1.Children.Count; i++)
                    {
                        CompareNodes(editorTree, node1.Children[i], node2.Children[i]);
                    }
                }
            }
#endif
        }

        public override bool Parse(ParseContext context, IAstNode parent) {
            TokenStream<RToken> tokens = context.Tokens;

            if (tokens.CurrentToken.IsVariableKind()) {
                var v = new Variable();
                v.Parse(context, this);

                // Variables don't set parent since during complex
                // exression parsing parent is determined by the
                // expression parser based on precedence and grouping.
                v.Parent = this; 
                this.Variable = v;

                if (tokens.CurrentToken.IsKeywordText(context.TextProvider, "in")) {
                    this.InOperator = new TokenNode();
                    this.InOperator.Parse(context, this);

                    this.Expression = new Expression(inGroup: true);
                    if (this.Expression.Parse(context, this)) {
                        return base.Parse(context, parent);
                    }
                } else {
                    context.AddError(new MissingItemParseError(ParseErrorType.InKeywordExpected, tokens.CurrentToken));
                }
            } else {
                context.AddError(new MissingItemParseError(ParseErrorType.IndentifierExpected, tokens.PreviousToken));
            }

            return false;
        }

        private void BuildAddIndexNode(IIndexDefinition index, IAstNode parent)
        {
            IAddIndexNode addIndexNode = new AddIndexNode(parent, index.Name);
            parent.ChildNodes.Add(addIndexNode);

            SemanticModelUtil.Copy(index, addIndexNode);
        }

        public override bool Parse(ParseContext context, IAstNode parent) {
            TokenStream<RToken> tokens = context.Tokens;

            Debug.Assert(context.Tokens.CurrentToken.TokenType == RTokenType.Identifier || 
                         context.Tokens.CurrentToken.TokenType == RTokenType.String);

            this.Identifier = RParser.ParseToken(context, this);
            this.EqualsSign = RParser.ParseToken(context, this);

            if (context.Tokens.CurrentToken.TokenType != RTokenType.Comma && context.Tokens.CurrentToken.TokenType != RTokenType.CloseBrace) {
                Expression exp = new Expression(inGroup: true);
                if (exp.Parse(context, this)) {
                    this.DefaultValue = exp;
                }
            } else {
                this.DefaultValue = new NullExpression();
                if (context.Tokens.IsEndOfStream()) {
                    context.AddError(new ParseError(ParseErrorType.ExpressionExpected, ErrorLocation.Token, context.Tokens.CurrentToken));
                } else {
                    context.AddError(new ParseError(ParseErrorType.ExpressionExpected, ErrorLocation.Token, EqualsSign));
                }
            }

            return base.Parse(context, parent);
        }

        protected override CommaSeparatedItem CreateItem(IAstNode parent, ParseContext context) {
            RToken currentToken = context.Tokens.CurrentToken;
            RToken nextToken = context.Tokens.NextToken;

            switch (currentToken.TokenType) {
                case RTokenType.Ellipsis:
                    return new EllipsisArgument();

                case RTokenType.Comma:
                    return new MissingArgument();

                case RTokenType.Identifier:
                case RTokenType.String:
                case RTokenType.Logical:
                case RTokenType.Complex:
                case RTokenType.NaN:
                case RTokenType.Null:
                case RTokenType.Number:
                case RTokenType.Infinity:
                    if (nextToken.TokenType == RTokenType.Operator && context.TextProvider.GetText(nextToken) == "=") {
                        return new NamedArgument();
                    }
                    break;

                case RTokenType.CloseBrace:
                    return null; // no arguments supplied
            }

            return new ExpressionArgument();
        }

        public override bool Parse(ParseContext context, IAstNode parent) {
            if (context.Tokens.CurrentToken.TokenType == RTokenType.Comma) {
                this.Comma = RParser.ParseToken(context, this);
            }

            return base.Parse(context, parent);
        }

        public static TokenNode ParseToken(ParseContext context, IAstNode parent) {
            TokenStream<RToken> tokens = context.Tokens;
            TokenNode node = new TokenNode();

            node.Parse(context, parent);
            return node;
        }

 protected override void DefaultVisit(IAstNode node)
 {
     foreach (var child in node.Children)
     {
         child.Accept(this);
     }
 }

        public override bool Parse(ParseContext context, IAstNode parent) {
            if (context.Tokens.CurrentToken.TokenType == RTokenType.OpenBrace) {
                context.AddError(new ParseError(ParseErrorType.UnexpectedToken, ErrorLocation.Token, context.Tokens.CurrentToken));
            }

            return false;
        }

        public override bool Parse(ParseContext context, IAstNode parent) {
            TokenStream<RToken> tokens = context.Tokens;

            Debug.Assert(tokens.CurrentToken.TokenType == RTokenType.Keyword);
            this.Keyword = RParser.ParseKeyword(context, this);
            this.Text = context.TextProvider.GetText(this.Keyword);

            if (tokens.CurrentToken.TokenType == RTokenType.OpenBrace) {
                this.OpenBrace = RParser.ParseToken(context, this);

                this.Arguments = new ArgumentList(RTokenType.CloseBrace);
                this.Arguments.Parse(context, this);

                if (tokens.CurrentToken.TokenType == RTokenType.CloseBrace) {
                    this.CloseBrace = RParser.ParseToken(context, this);
                    this.Scope = RParser.ParseScope(context, this, allowsSimpleScope: true, terminatingKeyword: null);
                    if (this.Scope != null) {
                        return base.Parse(context, parent);
                    } else {
                        context.AddError(new ParseError(ParseErrorType.FunctionBodyExpected, ErrorLocation.Token, tokens.PreviousToken));
                    }
                } else {
                    context.AddError(new ParseError(ParseErrorType.CloseBraceExpected, ErrorLocation.Token, tokens.CurrentToken));
                }
            } else {
                context.AddError(new ParseError(ParseErrorType.OpenBraceExpected, ErrorLocation.Token, tokens.CurrentToken));
            }

            return false;
        }

        public override bool Parse(ParseContext context, IAstNode parent) {
            if (ParseExpression(context) && this.Children.Count > 0) {
                return base.Parse(context, parent);
            }

            return false;
        }

 public StatementIndent(IAstNode node)
 {
     BeforeNode = node.BeforeNode;
     AfterNode = node;
     node.BeforeNode = this;
     ParentNode = (Statement)node.ParentNode;
 }

 public IAstNode CreateIAstNode(IAstNode beforeNode, string token)
 {
     if ((token[0] == '@' || token[0] == ':') && token.Length > 1)
     {
         // If the variable name is quoted
         if (token[1] == '"' || token[1] == '\'')
         {
             //_regex r2 = new _regex(@"^(((""[^""\\]*(?:\\.[^""\\]*)*(""|$))+)|(('[^'\\]*(?:\\.[^'\\]*)*('|$))+))\s");
             //TODO Valiable Node
             //return new ASTNode(   TokenType.VARIABLE
             //                ,   token[0] + r2.Match(token.Substring(1)).OriginalValue);
         }
         else
         {
             Match match = _regex.Match(token);
             if (match.Success)
             {
                 //TODO ValiableNode
                 //return new ASTNode(   TokenType.VARIABLE
                 //                ,   m3.OriginalValue
                 //                );
             }
         }
     }
     return null;
 }

        /// <summary>
        /// Abstract factory creating statements depending on current
        /// token and the following token sequence
        /// </summary>
        /// <returns></returns>
        public static IStatement Create(ParseContext context, IAstNode parent, string terminatingKeyword) {
            TokenStream<RToken> tokens = context.Tokens;
            RToken currentToken = tokens.CurrentToken;

            IStatement statement = null;

            switch (currentToken.TokenType) {
                case RTokenType.Keyword:
                    // If statement starts with a keyword, it is not an assignment
                    // hence we should always try keyword based statements first.
                    // Some of the statements may be R-values like typeof() but
                    // in case of the statement appearing on its own return value
                    // will be simply ignored. IDE may choose to show a warning.
                    if (currentToken.SubType == RTokenSubType.BuiltinFunction && tokens.NextToken.TokenType != RTokenType.OpenBrace) {
                        // 'return <- x + y' is allowed
                        statement = new ExpressionStatement(terminatingKeyword);
                    } else {
                        statement = KeywordStatement.CreateStatement(context, parent);
                    }
                    break;

                case RTokenType.Semicolon:
                    statement = new EmptyStatement();
                    break;

                default:
                    // Possible L-value in a left-hand assignment, 
                    // a function call or R-value in a right hand assignment.
                    statement = new ExpressionStatement(terminatingKeyword);
                    break;
            }

            return statement;
        }

        public void RemoveChildren(int start, int count) {
            if (count == 0)
                return;

            if (start < 0 || start >= Children.Count)
                throw new ArgumentOutOfRangeException("start");

            if (count < 0 || count > Children.Count || start + count > Children.Count)
                throw new ArgumentOutOfRangeException("count");

            if (Children.Count == count) {
                _children = new TextRangeCollection<IAstNode>();
            } else {
                var newChildren = new IAstNode[Children.Count - count];

                int j = 0;

                for (int i = 0; i < start; i++, j++)
                    newChildren[j] = Children[i];

                for (int i = start; i < start + count; i++)
                    Children[i].Parent = null;

                for (int i = start + count; i < Children.Count; i++, j++)
                    newChildren[j] = Children[i];

                _children = new TextRangeCollection<IAstNode>(newChildren);
            }
        }

        public TableOrColumnName(IAstNode preNode, string originalValue)
            : base(preNode, originalValue)
        {
            // SQLが成立していないとき
            if (ParentNode == null || ParentNode.ParentNode == null)
            {
                Order = OrderType.Unknown;
                throw new Exception("SQLが成立していません");
            }

            // 定義の親がStatementでその親が予約語
            if (ParentNode.ParentNode.GetType() == typeof (ReservedTopLevel))
            {
                string reservedWord = ParentNode.ParentNode.OriginalValue;
                Match m = _regex.Match(reservedWord);
                if (m.Success)
                {
                    // FROMやUPDATEなど、カラム名称が定義されない予約語ならテーブル名
                    Order = OrderType.Table;
                }
                else
                {
                    // SELECT句やWHERE区ででてきたカラム定義
                    Order = OrderType.Column;
                }
            }
            else
            {
                // JOIN句など、予約語とは違うネスト階層により出現する定義
                Order = OrderType.Column;
            }
        }

        public override bool Parse(ParseContext context, IAstNode parent) {
            // Remove comments from the token stream
            this.Comments = new CommentsCollection(context.Comments);

            GlobalScope globalScope = new GlobalScope();
            return globalScope.Parse(context, this);
        }

        public override bool Parse(ParseContext context, IAstNode parent) {
            // First parse base which should pick up keyword, braces, inner
            // expression and either full or simple (single statement) scope
            if (!base.Parse(context, parent)) {
                return false;
            }

            // At this point we should be either at 'else' token or 
            // at the next statement. In the latter case we are done.
            TokenStream<RToken> tokens = context.Tokens;

            if (tokens.CurrentToken.IsKeywordText(context.TextProvider, "else")) {
                bool allowLineBreak = AllowLineBreakBeforeElse(context);
                if (!allowLineBreak) {
                    // Verify that there is no line break before the 'else'
                    if (context.Tokens.IsLineBreakAfter(context.TextProvider, tokens.Position - 1)) {
                        context.AddError(new ParseError(ParseErrorType.UnexpectedToken, ErrorLocation.Token, tokens.CurrentToken));
                        return true;
                    }
                }
                this.Else = new KeywordScopeStatement(allowsSimpleScope: true);
                return this.Else.Parse(context, this);
            }

            // Not at 'else' so we are done here
            return true;
        }

        public override bool Parse(ParseContext context, IAstNode parent) {
            RToken currentToken = context.Tokens.CurrentToken;

            this.Token = currentToken;
            context.Tokens.MoveToNextToken();

            return base.Parse(context, parent);
        }

 public IAstNode CreateIAstNode(IAstNode beforeNode, string token)
 {
     if (token[0] == '(' || token[0] == ')')
     {
         return new Bracket(beforeNode, token[0].ToString());
     }
     return null;
 }