System.Data.BinaryNode.Optimize C# (CSharp) Method

        internal override ExpressionNode Optimize()
        {
            _left = _left.Optimize();

            if (_op == Operators.Is)
            {
                // only 'Is Null' or 'Is Not Null' are valid
                if (_right is UnaryNode)
                {
                    UnaryNode un = (UnaryNode)_right;
                    if (un._op != Operators.Not)
                    {
                        throw ExprException.InvalidIsSyntax();
                    }
                    _op = Operators.IsNot;
                    _right = un._right;
                }
                if (_right is ZeroOpNode)
                {
                    if (((ZeroOpNode)_right)._op != Operators.Null)
                    {
                        throw ExprException.InvalidIsSyntax();
                    }
                }
                else
                {
                    throw ExprException.InvalidIsSyntax();
                }
            }
            else
            {
                _right = _right.Optimize();
            }


            if (IsConstant())
            {
                object val = Eval();

                if (val == DBNull.Value)
                {
                    return new ZeroOpNode(Operators.Null);
                }

                if (val is bool)
                {
                    if ((bool)val)
                        return new ZeroOpNode(Operators.True);
                    else
                        return new ZeroOpNode(Operators.False);
                }
                return new ConstNode(table, ValueType.Object, val, false);
            }
            else
                return this;
        }