RequestQueryParser.cs source code in C# .NET

Source code for the .NET framework in C#

                        

Code:

/ 4.0 / 4.0 / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / DataWeb / Server / System / Data / Services / Parsing / RequestQueryParser.cs / 1607349 / RequestQueryParser.cs

                            //---------------------------------------------------------------------- 
// 
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//  
//      Provides a type to parse expressions in request queries.
//  
// 
// @owner  [....]
//--------------------------------------------------------------------- 

namespace System.Data.Services.Parsing
{
    #region Namespaces. 

    using System; 
    using System.Collections.Generic; 
    using System.Data.Services.Providers;
    using System.Diagnostics; 
    using System.Linq;
    using System.Linq.Expressions;
    using System.Reflection;
 
    #endregion Namespaces.
 
    ///  
    /// This class provides static methods to parse query options and compose
    /// them on an existing query. 
    /// 
    internal static class RequestQueryParser
    {
        #region Internal methods. 

        /// Sorts a query like a SQL ORDER BY clause does. 
        /// Service with data and configuration. 
        /// Original source for query.
        /// Ordering definition to compose. 
        /// The composed query.
        internal static IQueryable OrderBy(IDataService service, IQueryable source, OrderingInfo orderingInfo)
        {
            Debug.Assert(service != null, "service != null"); 
            Debug.Assert(source != null, "source != null");
            Debug.Assert(orderingInfo != null, "orderingInfo != null"); 
 
            Expression queryExpr = source.Expression;
            string methodAsc = "OrderBy"; 
            string methodDesc = "OrderByDescending";
            foreach (OrderingExpression o in orderingInfo.OrderingExpressions)
            {
                LambdaExpression selectorLambda = (LambdaExpression)o.Expression; 
                Type selectorType = selectorLambda.Body.Type;
                service.Provider.CheckIfOrderedType(selectorType); 
 
                queryExpr = Expression.Call(
                    typeof(Queryable), 
                    o.IsAscending ? methodAsc : methodDesc,
                    new Type[] { source.ElementType, selectorType },
                    queryExpr,
                    Expression.Quote(selectorLambda)); 

                methodAsc = "ThenBy"; 
                methodDesc = "ThenByDescending"; 
            }
 
            return source.Provider.CreateQuery(queryExpr);
        }

        /// Filters a query like a SQL WHERE clause does. 
        /// Service with data and configuration.
        /// Set for each item in the query if they are entities 
        /// Type for each item in the query in Astoria metadata terms 
        /// Original source for query.
        /// Predicate to compose. 
        /// The composed query.
        internal static IQueryable Where(IDataService service, ResourceSetWrapper setForIt, ResourceType typeForIt, IQueryable source, string predicate)
        {
            Debug.Assert(service != null, "service != null"); 
            Debug.Assert(typeForIt != null, "typeForIt != null");
            Debug.Assert(typeForIt.ResourceTypeKind != ResourceTypeKind.EntityType || setForIt != null, "setForIt cannot be null if typeForIt is an entity type."); 
            Debug.Assert(source != null, "source != null"); 
            Debug.Assert(predicate != null, "predicate != null");
 
            LambdaExpression lambda = ParseLambdaForWhere(service, setForIt, typeForIt, source.ElementType, predicate);
            return source.Provider.CreateQuery(
                Expression.Call(typeof(Queryable), "Where", new Type[] { source.ElementType }, source.Expression, Expression.Quote(lambda)));
        } 

        #endregion Internal methods. 
 
        #region Private methods.
 
        /// Parses a lambda expression.
        /// Service with data and configuration.
        /// Resource set for "it" contextual variable.
        /// Type for "it" contextual variable. 
        /// Actual (clr) element type for the sequence
        /// Expression to parse. 
        /// The parsed expression. 
        private static LambdaExpression ParseLambdaForWhere(IDataService service, ResourceSetWrapper setForIt, ResourceType typeForIt, Type queryElementType, string expression)
        { 
            Debug.Assert(service != null, "service != null");
            Debug.Assert(typeForIt != null, "typeForIt != null");
            Debug.Assert(typeForIt.ResourceTypeKind != ResourceTypeKind.EntityType || setForIt != null, "setForIt cannot be null if typeForIt is an entity type.");
            Debug.Assert(queryElementType != null, "queryElementType != null"); 
            Debug.Assert(expression != null, "expression != null");
            Debug.Assert(typeForIt.InstanceType == queryElementType, "typeForIt.InstanceType == queryElementType"); 
 
            ParameterExpression parameterForIt = Expression.Parameter(queryElementType, "it");
            ExpressionParser parser = new ExpressionParser(service, setForIt, typeForIt, parameterForIt, expression); 
            return Expression.Lambda(parser.ParseWhere(), parameterForIt);
        }

        #endregion Private methods. 

        /// Use this class to parse an expression in the Astoria URI format. 
        [DebuggerDisplay("ExpressionParser ({lexer.text})")] 
        internal class ExpressionParser
        { 
            #region Fields.

            /// Maximum recursion limit on deserializer.
            private const int RecursionLimit = 100; 

            /// A type that is not numeric. 
            private const int NumericTypeNotNumeric = 0; 

            /// A type that is a char, single, double or decimal. 
            private const int NumericTypeNotIntegral = 1;

            /// A type that is a signed integral.
            private const int NumericTypeSignedIntegral = 2; 

            /// A type that is an unsigned integral. 
            private const int NumericTypeUnsignedIntegral = 3; 

            /// Empty Expressions array. 
            private static readonly Expression[] emptyExpressions = new Expression[0];

            /// Constant for "true" literal.
            private static readonly ConstantExpression trueLiteral = Expression.Constant(true); 

            /// Constant for "false" literal. 
            private static readonly ConstantExpression falseLiteral = Expression.Constant(false); 

            /// Dictionary of system functions. 
            private static readonly Dictionary functions = FunctionDescription.CreateFunctions();

            /// Method info for string comparison
            private static readonly MethodInfo StringCompareMethodInfo = typeof(DataServiceProviderMethods) 
                                                                  .GetMethods(BindingFlags.Public | BindingFlags.Static)
                                                                  .Single(m => m.Name == "Compare" && m.GetParameters()[0].ParameterType == typeof(string)); 
 
            /// Method info for Bool comparison
            private static readonly MethodInfo BoolCompareMethodInfo = typeof(DataServiceProviderMethods) 
                                                                  .GetMethods(BindingFlags.Public | BindingFlags.Static)
                                                                  .Single(m => m.Name == "Compare" && m.GetParameters()[0].ParameterType == typeof(bool));

            /// Method info for Bool? comparison 
            private static readonly MethodInfo BoolCompareMethodInfoNullable = typeof(DataServiceProviderMethods)
                                                                  .GetMethods(BindingFlags.Public | BindingFlags.Static) 
                                                                  .Single(m => m.Name == "Compare" && m.GetParameters()[0].ParameterType == typeof(bool?)); 

            /// Method info for Guid comparison 
            private static readonly MethodInfo GuidCompareMethodInfo = typeof(DataServiceProviderMethods)
                                                                  .GetMethods(BindingFlags.Public | BindingFlags.Static)
                                                                  .Single(m => m.Name == "Compare" && m.GetParameters()[0].ParameterType == typeof(Guid));
 
            /// Method info for Guid? comparison
            private static readonly MethodInfo GuidCompareMethodInfoNullable = typeof(DataServiceProviderMethods) 
                                                                  .GetMethods(BindingFlags.Public | BindingFlags.Static) 
                                                                  .Single(m => m.Name == "Compare" && m.GetParameters()[0].ParameterType == typeof(Guid?));
 
            /// Method info for byte array comparison.
            private static readonly MethodInfo ByteArrayEqualMethod = typeof(ExpressionParser)
                                                                  .GetMethod("ByteArraysEqual", BindingFlags.NonPublic | BindingFlags.Static);
 
            /// Method info for byte array comparison.
            private static readonly MethodInfo ByteArrayNotEqualMethod = typeof(ExpressionParser) 
                                                                  .GetMethod("ByteArraysNotEqual", BindingFlags.NonPublic | BindingFlags.Static); 

            /// Provider of data and metadata. 
            private readonly DataServiceProviderWrapper provider;

            /// Service with data and configuration.
            private readonly IDataService service; 

            /// Resource set for "it" 
            private readonly ResourceSetWrapper setForIt; 

            /// Metadata type for "it" 
            private readonly ResourceType typeForIt;

            /// Literals.
            private Dictionary literals; 

            /// "it" contextual parameter. 
            private ParameterExpression it; 

            /// Expression lexer. 
            private ExpressionLexer lexer;

            /// Whether the expression tree should propagate nulls explicitly.
            private bool nullPropagationRequired; 

            /// Depth of recursion. 
            private int recursionDepth; 

            /// ResourceType and ResourceSet information for current segment. 
            private SegmentTypeInfo currentSegmentInfo;

            #endregion Fields.
 
            #region Constructors.
 
            /// Initializes a new . 
            /// Service with data and configuration.
            /// Resource set for "it" contextual variable 
            /// Type for "it" contextual variable
            /// Parameters for the current "it" context.
            /// Expression to parse.
            internal ExpressionParser(IDataService service, ResourceSetWrapper setForIt, ResourceType typeForIt, ParameterExpression parameterForIt, string expression) 
            {
                Debug.Assert(service != null, "service != null"); 
 
                // For Open types, we could potentially have typeForIt parameter set to null value,
                // However, we have decided not support ordering on Open properties which also implies 
                // that we can not have entity typed properties on Open types
                Debug.Assert(typeForIt != null, "typeForIt != null");

                Debug.Assert(expression != null, "expression != null"); 
                Debug.Assert(parameterForIt != null, "parameterForIt != null");
 
                this.service = service; 
                this.provider = service.Provider;
                this.nullPropagationRequired = this.provider.NullPropagationRequired; 
                this.literals = new Dictionary(ReferenceEqualityComparer.Instance);
                this.setForIt = setForIt;
                this.typeForIt = typeForIt;
                this.it = parameterForIt; 
                this.lexer = new ExpressionLexer(expression);
            } 
 
            #endregion Constructors.
 
            /// Current token being processed.
            private Token CurrentToken
            {
                get { return this.lexer.CurrentToken; } 
                set { this.lexer.CurrentToken = value; }
            } 
 
            /// Parses the text expression for a .Where method invocation.
            /// The parsed expression. 
            internal Expression ParseWhere()
            {
                int exprPos = this.lexer.Position;
                Expression expr = this.ParseExpression(); 

                expr = PrepareExpressionForWhere(expr); 
                if (expr.Type != typeof(bool)) 
                {
                    throw ParseError(Strings.RequestQueryParser_ExpressionTypeMismatch(WebUtil.GetTypeName(typeof(bool)), exprPos)); 
                }

                this.lexer.ValidateToken(TokenId.End);
                return expr; 
            }
 
            /// Makes the expression that is used as a filter corresponding to skip token. 
            /// Ordering expression.
            /// The provided skip token. 
            /// LambdaExpression corresponding to the skip token filter.
            internal LambdaExpression BuildSkipTokenFilter(OrderingInfo topLevelOrderingInfo, KeyInstance k)
            {
                ParameterExpression element = Expression.Parameter(this.typeForIt.InstanceType, "element"); 
                Expression lastCondition = Expression.Constant(true, typeof(bool));
                Expression lastMatch = Expression.Constant(false, typeof(bool)); 
 
                foreach (var v in WebUtil.Zip(topLevelOrderingInfo.OrderingExpressions, k.PositionalValues, (x, y) => new { Order = x, Value = y }))
                { 
                    Token comparisonExp = v.Order.IsAscending ? Token.GreaterThan : Token.LessThan;

                    Expression fixedLambda = System.Data.Services.Client.ParameterReplacerVisitor.Replace(
                                                    ((LambdaExpression)v.Order.Expression).Body, 
                                                    ((LambdaExpression)v.Order.Expression).Parameters[0],
                                                    element); 
 
                    Expression comparison = GenerateLogicalAnd(
                                                lastCondition, 
                                                this.GenerateNullAwareComparison(fixedLambda, (String)v.Value, comparisonExp));

                    lastMatch = GenerateLogicalOr(lastMatch, comparison);
 
                    lastCondition = GenerateLogicalAnd(
                                        lastCondition, 
                                        this.GenerateComparison(fixedLambda, (String)v.Value, Token.EqualsTo)); 
                }
 
                lastMatch = PrepareExpressionForWhere(lastMatch);

                Debug.Assert(lastMatch.Type == typeof(bool), "Skip token should generate boolean expression.");
 
                return Expression.Lambda(lastMatch, element);
            } 
 
            /// Parses the text expression for ordering.
            /// An enumeration of orderings. 
            internal IEnumerable ParseOrdering()
            {
                List orderings = new List();
                while (true) 
                {
                    Expression expr = this.ParseExpression(); 
                    bool ascending = true; 
                    if (this.TokenIdentifierIs(ExpressionConstants.KeywordAscending))
                    { 
                        this.lexer.NextToken();
                    }
                    else if (this.TokenIdentifierIs(ExpressionConstants.KeywordDescending))
                    { 
                        this.lexer.NextToken();
                        ascending = false; 
                    } 

                    orderings.Add(new OrderingExpression(expr, ascending)); 
                    if (this.CurrentToken.Id != TokenId.Comma)
                    {
                        break;
                    } 

                    this.lexer.NextToken(); 
                } 

                this.ValidateToken(TokenId.End); 
                return orderings;
            }

            /// Parse one of the literals of skip token. 
            /// Input literal.
            /// Object resulting from conversion of literal. 
            internal object ParseSkipTokenLiteral(String literal) 
            {
                ExpressionLexer l = new ExpressionLexer(literal); 
                Expression e = this.ParsePrimaryStart(l);
                if (e.NodeType != ExpressionType.Constant)
                {
                    throw new InvalidOperationException(Strings.RequsetQueryParser_ExpectingLiteralInSkipToken(literal)); 
                }
 
                return ((ConstantExpression)e).Value; 
            }
 
            /// Prepare the given expression for passing as a filter to Queryable.Where.
            /// Input expression.
            /// Expression converted to boolean expression.
            private static Expression PrepareExpressionForWhere(Expression expr) 
            {
                if (IsOpenPropertyExpression(expr)) 
                { 
                    expr = OpenTypeMethods.EqualExpression(expr, Expression.Constant(true, typeof(object)));
                    expr = Expression.Convert(expr, typeof(bool)); 
                }
                else if (WebUtil.IsNullConstant(expr))
                {
                    expr = falseLiteral; 
                }
                else if (expr.Type == typeof(bool?)) 
                { 
                    Expression test = Expression.Equal(expr, Expression.Constant(null, typeof(bool?)));
                    expr = Expression.Condition(test, falseLiteral, Expression.Property(expr, "Value")); 
                }

                return expr;
            } 

            /// Compares two byte arrays for equality. 
            /// First byte array.Second byte array. 
            /// true if the arrays are equal; false otherwise.
            private static bool ByteArraysEqual(byte[] b0, byte[] b1) 
            {
                if (b0 == b1)
                {
                    return true; 
                }
 
                if (b0 == null || b1 == null) 
                {
                    return false; 
                }

                if (b0.Length != b1.Length)
                { 
                    return false;
                } 
 
                for (int i = 0; i < b0.Length; i++)
                { 
                    if (b0[i] != b1[i])
                    {
                        return false;
                    } 
                }
 
                return true; 
            }
 
            /// Compares two byte arrays for equality.
            /// First byte array.Second byte array.
            /// true if the arrays are not equal; false otherwise.
            private static bool ByteArraysNotEqual(byte[] b0, byte[] b1) 
            {
                return !ByteArraysEqual(b0, b1); 
            } 

            /// Gets a non-nullable version of the specified type. 
            /// Type to get non-nullable version for.
            /// 
            ///  if type is a reference type or a
            /// non-nullable type; otherwise, the underlying value type. 
            /// 
            private static Type GetNonNullableType(Type type) 
            { 
                return Nullable.GetUnderlyingType(type) ?? type;
            } 

            /// Checks whether the specified type is a signed integral type.
            /// Type to check.
            /// true if  is a signed integral type; false otherwise. 
            private static bool IsSignedIntegralType(Type type)
            { 
                return GetNumericTypeKind(type) == NumericTypeSignedIntegral; 
            }
 
            /// Checks whether the specified type is an unsigned integral type.
            /// Type to check.
            /// true if  is an unsigned integral type; false otherwise.
            private static bool IsUnsignedIntegralType(Type type) 
            {
                return GetNumericTypeKind(type) == NumericTypeUnsignedIntegral; 
            } 

            /// Gets a flag for the numeric kind of type. 
            /// Type to get numeric kind for.
            /// 
            /// One of NumericTypeNotNumeric; NumericTypeNotIntegral if it's char,
            /// single, double or decimal; NumericTypeSignedIntegral, or NumericTypeUnsignedIntegral. 
            /// 
            private static int GetNumericTypeKind(Type type) 
            { 
                type = GetNonNullableType(type);
                Debug.Assert(!type.IsEnum, "!type.IsEnum"); 
                switch (Type.GetTypeCode(type))
                {
                    case TypeCode.Char:
                    case TypeCode.Single: 
                    case TypeCode.Double:
                    case TypeCode.Decimal: 
                        return NumericTypeNotIntegral; 
                    case TypeCode.SByte:
                    case TypeCode.Int16: 
                    case TypeCode.Int32:
                    case TypeCode.Int64:
                        return NumericTypeSignedIntegral;
                    case TypeCode.Byte: 
                        return NumericTypeUnsignedIntegral;
                    default: 
                        return NumericTypeNotNumeric; 
                }
            } 

            /// Checks whether type is a (possibly nullable) enumeration type.
            /// Type to check.
            /// true if type is an enumeration or a nullable enumeration; false otherwise. 
            private static bool IsEnumType(Type type)
            { 
                return GetNonNullableType(type).IsEnum; 
            }
 
            /// Returns an object that can enumerate the specified type and its supertypes.
            /// Type to based enumeration on.
            /// An object that can enumerate the specified type and its supertypes.
            private static IEnumerable SelfAndBaseTypes(Type type) 
            {
                if (type.IsInterface) 
                { 
                    List types = new List();
                    AddInterface(types, type); 
                    return types;
                }

                return SelfAndBaseClasses(type); 
            }
 
            /// Returns an object that can enumerate the specified type and its supertypes. 
            /// Type to based enumeration on.
            /// An object that can enumerate the specified type and its supertypes. 
            private static IEnumerable SelfAndBaseClasses(Type type)
            {
                while (type != null)
                { 
                    yield return type;
                    type = type.BaseType; 
                } 
            }
 
            /// Adds an interface type to a list of types, including inherited interfaces.
            /// Types list ot add to.
            /// Interface type to add.
            private static void AddInterface(List types, Type type) 
            {
                if (!types.Contains(type)) 
                { 
                    types.Add(type);
                    foreach (Type t in type.GetInterfaces()) 
                    {
                        AddInterface(types, t);
                    }
                } 
            }
 
            /// Finds the best applicable methods from the specified array that match the arguments. 
            /// Candidate methods.
            /// Argument expressions. 
            /// Best applicable methods.
            private static MethodData[] FindBestApplicableMethods(MethodData[] applicable, Expression[] args)
            {
                Debug.Assert(applicable != null, "applicable != null"); 

                List result = new List(); 
                foreach (MethodData method in applicable) 
                {
                    bool betterThanAllOthers = true; 
                    foreach (MethodData otherMethod in applicable)
                    {
                        if (otherMethod != method && IsBetterThan(args, otherMethod, method))
                        { 
                            betterThanAllOthers = false;
                            break; 
                        } 
                    }
 
                    if (betterThanAllOthers)
                    {
                        result.Add(method);
                    } 
                }
 
                return result.ToArray(); 
            }
 
            /// Parses the specified text into a number.
            /// Text to parse.
            /// Type to parse into.
            /// The parsed number. 
            private static object ParseNumber(string text, Type type)
            { 
                TypeCode tc = Type.GetTypeCode(GetNonNullableType(type)); 
                switch (tc)
                { 
                    case TypeCode.SByte:
                        sbyte sb;
                        if (sbyte.TryParse(text, out sb))
                        { 
                            return sb;
                        } 
 
                        break;
                    case TypeCode.Byte: 
                        byte b;
                        if (byte.TryParse(text, out b))
                        {
                            return b; 
                        }
 
                        break; 
                    case TypeCode.Int16:
                        short s; 
                        if (short.TryParse(text, out s))
                        {
                            return s;
                        } 

                        break; 
                    case TypeCode.Int32: 
                        int i;
                        if (int.TryParse(text, out i)) 
                        {
                            return i;
                        }
 
                        break;
                    case TypeCode.Int64: 
                        long l; 
                        if (long.TryParse(text, out l))
                        { 
                            return l;
                        }

                        break; 
                    case TypeCode.Single:
                        float f; 
                        if (float.TryParse(text, out f)) 
                        {
                            return f; 
                        }

                        break;
                    case TypeCode.Double: 
                        double d;
                        if (double.TryParse(text, out d)) 
                        { 
                            return d;
                        } 

                        break;
                    case TypeCode.Decimal:
                        decimal e; 
                        if (decimal.TryParse(text, out e))
                        { 
                            return e; 
                        }
 
                        break;
                }

                return null; 
            }
 
            /// Checks whether the source type is compatible with the value type. 
            /// Source type.
            /// Target type. 
            /// true if source can be used in place of target; false otherwise.
            private static bool IsCompatibleWith(Type source, Type target)
            {
                if (source == target) 
                {
                    return true; 
                } 

                if (!target.IsValueType) 
                {
                    return target.IsAssignableFrom(source);
                }
 
                Type sourceType = GetNonNullableType(source);
                Type targetType = GetNonNullableType(target); 
 
                //// This rule stops the parser from considering nullable types as incompatible
                //// with non-nullable types. We have however implemented this rule because we just 
                //// access underlying rules. C# requires an explicit .Value access, and EDM has no
                //// nullablity on types and (at the model level) implements null propagation.
                ////
                //// if (sourceType != source && targetType == target) 
                //// {
                ////     return false; 
                //// } 

                TypeCode sourceCode = sourceType.IsEnum ? TypeCode.Object : Type.GetTypeCode(sourceType); 
                TypeCode targetCode = targetType.IsEnum ? TypeCode.Object : Type.GetTypeCode(targetType);
                switch (sourceCode)
                {
                    case TypeCode.SByte: 
                        switch (targetCode)
                        { 
                            case TypeCode.SByte: 
                            case TypeCode.Int16:
                            case TypeCode.Int32: 
                            case TypeCode.Int64:
                            case TypeCode.Single:
                            case TypeCode.Double:
                            case TypeCode.Decimal: 
                                return true;
                        } 
 
                        break;
                    case TypeCode.Byte: 
                        switch (targetCode)
                        {
                            case TypeCode.Byte:
                            case TypeCode.Int16: 
                            case TypeCode.Int32:
                            case TypeCode.Int64: 
                            case TypeCode.Single: 
                            case TypeCode.Double:
                            case TypeCode.Decimal: 
                                return true;
                        }

                        break; 
                    case TypeCode.Int16:
                        switch (targetCode) 
                        { 
                            case TypeCode.Int16:
                            case TypeCode.Int32: 
                            case TypeCode.Int64:
                            case TypeCode.Single:
                            case TypeCode.Double:
                            case TypeCode.Decimal: 
                                return true;
                        } 
 
                        break;
                    case TypeCode.Int32: 
                        switch (targetCode)
                        {
                            case TypeCode.Int32:
                            case TypeCode.Int64: 
                            case TypeCode.Single:
                            case TypeCode.Double: 
                            case TypeCode.Decimal: 
                                return true;
                        } 

                        break;
                    case TypeCode.Int64:
                        switch (targetCode) 
                        {
                            case TypeCode.Int64: 
                            case TypeCode.Single: 
                            case TypeCode.Double:
                            case TypeCode.Decimal: 
                                return true;
                        }

                        break; 
                    case TypeCode.Single:
                        switch (targetCode) 
                        { 
                            case TypeCode.Single:
                            case TypeCode.Double: 
                                return true;
                        }

                        break; 
                    default:
                        if (sourceType == targetType) 
                        { 
                            return true;
                        } 

                        break;
                }
 
                // Anything can be converted to something that's *exactly* an object.
                if (target == typeof(object)) 
                { 
                    return true;
                } 

                return false;
            }
 
            /// 
            /// Checks whether one type list is a better fit than other for the 
            /// specified expressions. 
            /// 
            /// Expressions for arguments. 
            /// First type list to check.
            /// Second type list to check.
            /// 
            /// true if  has better parameter matching than . 
            /// 
            private static bool IsBetterThan(Expression[] args, IEnumerable firstCandidate, IEnumerable secondCandidate) 
            { 
                bool better = false;
 
                using (IEnumerator first = firstCandidate.GetEnumerator())
                using (IEnumerator second = secondCandidate.GetEnumerator())
                {
                    for (int i = 0; i < args.Length; i++) 
                    {
                        first.MoveNext(); 
                        second.MoveNext(); 
                        int c = CompareConversions(args[i].Type, first.Current, second.Current);
                        if (c < 0) 
                        {
                            return false;
                        }
                        else if (c > 0) 
                        {
                            better = true; 
                        } 
                    }
                } 

                return better;
            }
 
            /// 
            /// Checks whether one method is a better fit than other for the 
            /// specified expressions. 
            /// 
            /// Expressions for arguments. 
            /// First method to check.
            /// Second method to check.
            /// 
            /// true if  has better parameter matching than . 
            /// 
            private static bool IsBetterThan(Expression[] args, MethodData m1, MethodData m2) 
            { 
                Debug.Assert(args != null, "args != null");
                Debug.Assert(m1 != null, "m1 != null"); 
                Debug.Assert(m2 != null, "m2 != null");
                return IsBetterThan(args, m1.ParameterTypes, m2.ParameterTypes);
            }
 
            /// Checks which conversion is better.
            /// Source type. 
            /// First candidate type to convert to. 
            /// Second candidate type to convert to.
            ///  
            /// Return 1 if s -> t1 is a better conversion than s -> t2
            /// Return -1 if s -> t2 is a better conversion than s -> t1
            /// Return 0 if neither conversion is better
            ///  
            private static int CompareConversions(Type source, Type targetA, Type targetB)
            { 
                // If both types are exactly the same, there is no preference. 
                if (targetA == targetB)
                { 
                    return 0;
                }

                // Look for exact matches. 
                if (source == targetA)
                { 
                    return 1; 
                }
                else if (source == targetB) 
                {
                    return -1;
                }
 
                // If one is compatible and the other is not, choose the compatible type.
                bool compatibleT1AndT2 = IsCompatibleWith(targetA, targetB); 
                bool compatibleT2AndT1 = IsCompatibleWith(targetB, targetA); 
                if (compatibleT1AndT2 && !compatibleT2AndT1)
                { 
                    return 1;
                }
                else if (compatibleT2AndT1 && !compatibleT1AndT2)
                { 
                    return -1;
                } 
 
                // Prefer to keep the original nullability.
                bool sourceNullable = WebUtil.IsNullableType(source); 
                bool typeNullableA = WebUtil.IsNullableType(targetA);
                bool typeNullableB = WebUtil.IsNullableType(targetB);
                if (sourceNullable == typeNullableA && sourceNullable != typeNullableB)
                { 
                    return 1;
                } 
                else if (sourceNullable != typeNullableA && sourceNullable == typeNullableB) 
                {
                    return -1; 
                }

                // Prefer signed to unsigned.
                if (IsSignedIntegralType(targetA) && IsUnsignedIntegralType(targetB)) 
                {
                    return 1; 
                } 
                else if (IsSignedIntegralType(targetB) && IsUnsignedIntegralType(targetA))
                { 
                    return -1;
                }

                // Prefer non-object to object. 
                if (targetA != typeof(object) && targetB == typeof(object))
                { 
                    return 1; 
                }
                else if (targetB != typeof(object) && targetA == typeof(object)) 
                {
                    return -1;
                }
 
                return 0;
            } 
 
            /// Generates an Equal expression.
            /// Left expression. 
            /// Right expression.
            /// The generated expression.
            private static Expression GenerateEqual(Expression left, Expression right)
            { 
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.EqualExpression(left, right); 
                }
 
                if (left.Type == typeof(byte[]))
                {
                    return Expression.Equal(left, right, false, ExpressionParser.ByteArrayEqualMethod);
                } 

                return Expression.Equal(left, right); 
            } 

            /// Generates a NotEqual expression. 
            /// Left expression.
            /// Right expression.
            /// The generated expression.
            private static Expression GenerateNotEqual(Expression left, Expression right) 
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right)) 
                { 
                    return OpenTypeMethods.NotEqualExpression(left, right);
                } 

                if (left.Type == typeof(byte[]))
                {
                    return Expression.NotEqual(left, right, false, ExpressionParser.ByteArrayNotEqualMethod); 
                }
 
                return Expression.NotEqual(left, right); 
            }
 
            /// Generates a GreaterThan comparison expression.
            /// Left expression.
            /// Right expression.
            /// MethodInfo for comparison method used for string, bool, guid types 
            /// The generated expression.
            private static Expression GenerateGreaterThan(Expression left, Expression right, MethodInfo comparisonMethodInfo) 
            { 
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.GreaterThanExpression(left, right);
                }

                if (comparisonMethodInfo != null) 
                {
                    left = Expression.Call(null, comparisonMethodInfo, left, right); 
                    right = Expression.Constant(0, typeof(int)); 
                }
 
                return Expression.GreaterThan(left, right);
            }

            /// Generates a GreaterThanOrEqual comparsion expression. 
            /// Left expression.
            /// Right expression. 
            /// MethodInfo for comparison method used for string, bool, guid types 
            /// The generated expression.
            private static Expression GenerateGreaterThanEqual(Expression left, Expression right, MethodInfo comparisonMethodInfo) 
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                {
                    return OpenTypeMethods.GreaterThanOrEqualExpression(left, right); 
                }
 
                if (comparisonMethodInfo != null) 
                {
                    left = Expression.Call(null, comparisonMethodInfo, left, right); 
                    right = Expression.Constant(0, typeof(int));
                }

                return Expression.GreaterThanOrEqual(left, right); 
            }
 
            /// Generates a LessThan comparsion expression. 
            /// Left expression.
            /// Right expression. 
            /// MethodInfo for comparison method used for string, bool, guid types
            /// The generated expression.
            private static Expression GenerateLessThan(Expression left, Expression right, MethodInfo comparisonMethodInfo)
            { 
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.LessThanExpression(left, right); 
                }
 
                if (comparisonMethodInfo != null)
                {
                    left = Expression.Call(null, comparisonMethodInfo, left, right);
                    right = Expression.Constant(0, typeof(int)); 
                }
 
                return Expression.LessThan(left, right); 
            }
 
            /// Generates a LessThanOrEqual comparsion expression.
            /// Left expression.
            /// Right expression.
            /// MethodInfo for comparison method used for string, bool, guid types 
            /// The generated expression.
            private static Expression GenerateLessThanEqual(Expression left, Expression right, MethodInfo comparisonMethodInfo) 
            { 
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.LessThanOrEqualExpression(left, right);
                }

                if (comparisonMethodInfo != null) 
                {
                    left = Expression.Call(null, comparisonMethodInfo, left, right); 
                    right = Expression.Constant(0, typeof(int)); 
                }
 
                return Expression.LessThanOrEqual(left, right);
            }

            ///  
            /// Compares 2 strings by ordinal, used to obtain MethodInfo for comparison operator expression parameter
            ///  
            /// Left Parameter 
            /// Right Parameter
            /// 0 for equality, -1 for left less than right, 1 for left greater than right 
            /// 
            /// Do not change the name of this function because LINQ to SQL is sensitive about the
            /// method name, so is EF probably.
            ///  
            private static int Compare(String left, String right)
            { 
                return Comparer.Default.Compare(left, right); 
            }
 
            /// 
            /// Compares 2 booleans with true greater than false, used to obtain MethodInfo for comparison operator expression parameter
            /// 
            /// Left Parameter 
            /// Right Parameter
            /// 0 for equality, -1 for left less than right, 1 for left greater than right 
            ///  
            /// Do not change the name of this function because LINQ to SQL is sensitive about the
            /// method name, so is EF probably. 
            /// 
            [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.MSInternal", "CA908:AvoidTypesThatRequireJitCompilationInPrecompiledAssemblies", Justification = "Need implementation")]
            private static int Compare(bool left, bool right)
            { 
                return Comparer.Default.Compare(left, right);
            } 
 
            /// 
            /// Compares 2 nullable booleans with true greater than false, used to obtain MethodInfo for comparison operator expression parameter 
            /// 
            /// Left Parameter
            /// Right Parameter
            /// 0 for equality, -1 for left less than right, 1 for left greater than right 
            /// 
            /// Do not change the name of this function because LINQ to SQL is sensitive about the 
            /// method name, so is EF probably. 
            /// 
            [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.MSInternal", "CA908:AvoidTypesThatRequireJitCompilationInPrecompiledAssemblies", Justification = "Need implementation")] 
            private static int Compare(bool? left, bool? right)
            {
                return Comparer.Default.Compare(left, right);
            } 

            ///  
            /// Compares 2 guids by byte order, used to obtain MethodInfo for comparison operator expression parameter 
            /// 
            /// Left Parameter 
            /// Right Parameter
            /// 0 for equality, -1 for left less than right, 1 for left greater than right
            /// 
            /// Do not change the name of this function because LINQ to SQL is sensitive about the 
            /// method name, so is EF probably.
            ///  
            [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.MSInternal", "CA908:AvoidTypesThatRequireJitCompilationInPrecompiledAssemblies", Justification = "Need implementation")] 
            private static int Compare(Guid left, Guid right)
            { 
                return Comparer.Default.Compare(left, right);
            }

            ///  
            /// Compares 2 nullable guids by byte order, used to obtain MethodInfo for comparison operator expression parameter
            ///  
            /// Left Parameter 
            /// Right Parameter
            /// 0 for equality, -1 for left less than right, 1 for left greater than right 
            /// 
            /// Do not change the name of this function because LINQ to SQL is sensitive about the
            /// method name, so is EF probably.
            ///  
            [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.MSInternal", "CA908:AvoidTypesThatRequireJitCompilationInPrecompiledAssemblies", Justification = "Need implementation")]
            private static int Compare(Guid? left, Guid? right) 
            { 
                return Comparer.Default.Compare(left, right);
            } 

            /// Generates an addition expression.
            /// Left expression.
            /// Right expression. 
            /// The generated expression.
            private static Expression GenerateAdd(Expression left, Expression right) 
            { 
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.AddExpression(left, right);
                }

                return Expression.Add(left, right); 
            }
 
            /// Generates a subtract expression. 
            /// Left expression.
            /// Right expression. 
            /// The generated expression.
            private static Expression GenerateSubtract(Expression left, Expression right)
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right)) 
                {
                    return OpenTypeMethods.SubtractExpression(left, right); 
                } 

                return Expression.Subtract(left, right); 
            }

            /// Generates a multiplication expression.
            /// Left expression. 
            /// Right expression.
            /// The generated expression. 
            private static Expression GenerateMultiply(Expression left, Expression right) 
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right)) 
                {
                    return OpenTypeMethods.MultiplyExpression(left, right);
                }
 
                return Expression.Multiply(left, right);
            } 
 
            /// Generates a negative of expression.
            /// Input expression. 
            /// The generated expression.
            private static Expression GenerateNegate(Expression expr)
            {
                if (IsOpenPropertyExpression(expr)) 
                {
                    return OpenTypeMethods.NegateExpression(expr); 
                } 

                return Expression.Negate(expr); 
            }

            /// Generates a not of expression.
            /// Input expression. 
            /// The generated expression.
            private static Expression GenerateNot(Expression expr) 
            { 
                if (IsOpenPropertyExpression(expr))
                { 
                    return OpenTypeMethods.NotExpression(expr);
                }

                if (expr.Type == typeof(bool) || expr.Type == typeof(Nullable)) 
                {
                    // Expression.Not will take numerics and apply '~' to them, thus the extra check here. 
                    return Expression.Not(expr); 
                }
                else 
                {
                    throw ParseError(Strings.RequestQueryParser_NotDoesNotSupportType(expr.Type));
                }
            } 

            /// Generates a divide expression. 
            /// Left expression. 
            /// Right expression.
            /// The generated expression. 
            private static Expression GenerateDivide(Expression left, Expression right)
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.DivideExpression(left, right);
                } 
 
                return Expression.Divide(left, right);
            } 

            /// Generates a modulo expression.
            /// Left expression.
            /// Right expression. 
            /// The generated expression.
            private static Expression GenerateModulo(Expression left, Expression right) 
            { 
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.ModuloExpression(left, right);
                }

                return Expression.Modulo(left, right); 
            }
 
            /// Generates a logical And expression. 
            /// Left expression.
            /// Right expression. 
            /// The generated expression.
            private static Expression GenerateLogicalAnd(Expression left, Expression right)
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right)) 
                {
                    return OpenTypeMethods.AndAlsoExpression(left, right); 
                } 

                return Expression.AndAlso(left, right); 
            }

            /// Generates a Logical Or expression.
            /// Left expression. 
            /// Right expression.
            /// The generated expression. 
            private static Expression GenerateLogicalOr(Expression left, Expression right) 
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right)) 
                {
                    return OpenTypeMethods.OrElseExpression(left, right);
                }
 
                return Expression.OrElse(left, right);
            } 
 
            /// 
            /// Checks whether the specified  is part of an open property expression. 
            /// 
            /// Non-null  to check.
            /// true if  is based on an open property; false otherwise.
            private static bool IsOpenPropertyExpression(Expression expression) 
            {
                Debug.Assert(expression != null, "expression != null"); 
                return expression != WebUtil.NullLiteral && expression.Type == typeof(object) && IsOpenExpression(expression); 
            }
 
            /// Checks if the given input expression refers to open types.
            /// Input expression.
            /// true if the input is an open expression, false otherwise.
            private static bool IsOpenExpression(Expression input) 
            {
                Debug.Assert(input != null, "input != null"); 
                input = StripObjectConvert(input); 

                switch (input.NodeType) 
                {
                    case ExpressionType.Call:
                        return ((MethodCallExpression)input).Method.DeclaringType == typeof(OpenTypeMethods);
 
                    case ExpressionType.Negate:
                    case ExpressionType.Not: 
                        return ((UnaryExpression)input).Method != null && ((UnaryExpression)input).Method.DeclaringType == typeof(OpenTypeMethods); 

                    case ExpressionType.Add: 
                    case ExpressionType.AndAlso:
                    case ExpressionType.Divide:
                    case ExpressionType.Equal:
                    case ExpressionType.GreaterThan: 
                    case ExpressionType.GreaterThanOrEqual:
                    case ExpressionType.LessThan: 
                    case ExpressionType.LessThanOrEqual: 
                    case ExpressionType.Modulo:
                    case ExpressionType.Multiply: 
                    case ExpressionType.NotEqual:
                    case ExpressionType.OrElse:
                    case ExpressionType.Subtract:
                        return ((BinaryExpression)input).Method != null && ((BinaryExpression)input).Method.DeclaringType == typeof(OpenTypeMethods); 

                    case ExpressionType.Conditional: 
                        // This handles that null propagation scenario. 
                        return IsOpenExpression(((ConditionalExpression)input).IfFalse);
 
                    case ExpressionType.Convert:
                    case ExpressionType.Constant:
                    case ExpressionType.MemberAccess:
                    case ExpressionType.TypeIs: 
                        return false;
 
                    default: 
                        Debug.Assert(false, "Unexpected expression type found.");
                        break; 
                }

                return false;
            } 

            /// Strips all Expression.Convert(object) calls from the input expression. 
            /// Input expression. 
            /// First non-Convert expression inside Converts that converts to non-object type.
            private static Expression StripObjectConvert(Expression input) 
            {
                Debug.Assert(input != null, "input != null");
                while (input.NodeType == ExpressionType.Convert && input.Type == typeof(object))
                { 
                    UnaryExpression inner = (UnaryExpression)input;
                    input = inner.Operand; 
                } 

                return input; 
            }

            /// Gets a static method by name.
            /// Name of method to get. 
            /// Left expression to resolve method from and to use as argument.
            /// Right expression. 
            /// The method. 
            private static MethodInfo GetStaticMethod(string methodName, Expression left, Expression right)
            { 
                return left.Type.GetMethod(methodName, new Type[] { left.Type, right.Type });
            }

            /// Generates a static method call. 
            /// Method name.
            /// Left expression. 
            /// Right expression. 
            /// The generated expression.
            private static Expression GenerateStaticMethodCall(string methodName, Expression left, Expression right) 
            {
                return Expression.Call(null, GetStaticMethod(methodName, left, right), new Expression[] { left, right });
            }
 
            /// Creates an exception for a parse error.
            /// Message text. 
            /// A new Exception. 
            private static Exception ParseError(string message)
            { 
                return DataServiceException.CreateSyntaxError(message);
            }

            /// Checks that the given token has the specified identifier. 
            /// Token to check
            /// Identifier to check. 
            /// true if  is an identifier with the specified text. 
            private static bool TokenIdentifierIs(Token token, string id)
            { 
                return token.Id == TokenId.Identifier && String.Equals(id, token.Text, StringComparison.OrdinalIgnoreCase);
            }

            /// Creates an exception indicated that two operands are incompatible. 
            /// Name of operation for operands.
            /// Expression for left-hand operand. 
            /// Expression for right-hand operand. 
            /// Position for error.
            /// A new . 
            private static Exception IncompatibleOperandsError(string operationName, Expression left, Expression right, int pos)
            {
                string message = Strings.RequestQueryParser_IncompatibleOperands(
                    operationName, 
                    WebUtil.GetTypeName(left.Type),
                    WebUtil.GetTypeName(right.Type), 
                    pos); 
                return ParseError(message);
            } 

            #region Parsing.

            /// Handles 'null' literals. 
            /// Lexer to use for reading tokens
            /// The parsed expression. 
            private static Expression ParseNullLiteral(ExpressionLexer l) 
            {
                Debug.Assert(l.CurrentToken.Id == TokenId.NullLiteral, "l.CurrentToken.Id == TokenId.NullLiteral"); 
                l.NextToken();
                return WebUtil.NullLiteral;
            }
 
            /// Handles a ?: operator - not supported.
            /// The parsed expression. 
            private Expression ParseExpression() 
            {
                this.RecurseEnter(); 
                Expression expr = this.ParseLogicalOr();
                this.RecurseLeave();
                return expr;
            } 

            /// Handles or operator. 
            /// The parsed expression. 
            private Expression ParseLogicalOr()
            { 
                this.RecurseEnter();
                Expression left = this.ParseLogicalAnd();
                while (this.TokenIdentifierIs(ExpressionConstants.KeywordOr))
                { 
                    Token op = this.CurrentToken;
                    this.lexer.NextToken(); 
                    Expression right = this.ParseLogicalAnd(); 
                    this.CheckAndPromoteOperands(typeof(OperationSignatures.ILogicalSignatures), op.Text, ref left, ref right, op.Position);
                    left = GenerateLogicalOr(left, right); 
                }

                this.RecurseLeave();
                return left; 
            }
 
            /// Handles and operator. 
            /// The parsed expression.
            private Expression ParseLogicalAnd() 
            {
                this.RecurseEnter();
                Expression left = this.ParseComparison();
                while (this.TokenIdentifierIs(ExpressionConstants.KeywordAnd)) 
                {
                    Token op = this.CurrentToken; 
                    this.lexer.NextToken(); 
                    Expression right = this.ParseComparison();
                    this.CheckAndPromoteOperands(typeof(OperationSignatures.ILogicalSignatures), op.Text, ref left, ref right, op.Position); 
                    left = GenerateLogicalAnd(left, right);
                }

                this.RecurseLeave(); 
                return left;
            } 
 
            /// Handles eq, ne, lt, gt, le, ge operators.
            /// The parsed expression. 
            private Expression ParseComparison()
            {
                this.RecurseEnter();
                Expression left = this.ParseAdditive(); 
                while (this.CurrentToken.IsComparisonOperator)
                { 
                    Token op = this.CurrentToken; 
                    this.lexer.NextToken();
                    Expression right = this.ParseAdditive(); 
                    left = this.GenerateComparisonExpression(left, right, op);
                }

                this.RecurseLeave(); 
                return left;
            } 
 
            /// 
            /// Generates a comparison expression given a left hand side expression and literal for right hand side 
            /// 
            /// Left hand side experssions
            /// Literal for right hand side
            /// gt, eq or lt operator token 
            /// Resulting comparison expression
            private Expression GenerateComparison(Expression left, String rightLiteral, Token op) 
            { 
                ExpressionLexer l = new ExpressionLexer(rightLiteral);
                return this.GenerateComparisonExpression(left, this.ParsePrimaryStart(l), op); 
            }

            /// 
            /// Generates a comparison expression which can handle NULL values for any type. 
            /// NULL is always treated as the smallest possible value.
            /// So for example for strings NULL is smaller than any non-NULL string. 
            /// For now only GreaterThan and LessThan operators are supported by this method. 
            /// 
            /// Left hand side expression 
            /// Literal for the right hand side
            /// gt or lt operator token
            /// Resulting comparison expression (has a Boolean value)
            private Expression GenerateNullAwareComparison(Expression left, String rightLiteral, Token op) 
            {
                Debug.Assert( 
                    op.Text == ExpressionConstants.KeywordGreaterThan || op.Text == ExpressionConstants.KeywordLessThan, 
                    "Only GreaterThan or LessThan operators are supported by the GenerateNullAwateComparison method for now.");
 
                ExpressionLexer l = new ExpressionLexer(rightLiteral);
                Expression right = this.ParsePrimaryStart(l);

                if (WebUtil.TypeAllowsNull(left.Type)) 
                {
                    if (!WebUtil.TypeAllowsNull(right.Type)) 
                    { 
                        right = Expression.Convert(right, typeof(Nullable<>).MakeGenericType(right.Type));
                    } 
                }
                else if (WebUtil.TypeAllowsNull(right.Type))
                {
                    left = Expression.Convert(left, typeof(Nullable<>).MakeGenericType(left.Type)); 
                }
                else 
                { 
                    // Can't perform NULL aware comparison on this type. Just let the normal
                    // comparison deal with it. Since the type doesn't allow NULL one should 
                    // never appear, so normal comparison is just fine.
                    return this.GenerateComparisonExpression(left, right, op);
                }
 
                switch (op.Text)
                { 
                    case ExpressionConstants.KeywordGreaterThan: 
                        // (left != null) && ((right == null) || Compare(left, right) > 0)
                        if (left == WebUtil.NullLiteral) 
                        {
                            return Expression.Constant(false, typeof(bool));
                        }
                        else if (right == WebUtil.NullLiteral) 
                        {
                            return GenerateNotEqual(left, Expression.Constant(null, left.Type)); 
                        } 
                        else
                        { 
                            return GenerateLogicalAnd(
                                        GenerateNotEqual(left, Expression.Constant(null, left.Type)),
                                        GenerateLogicalOr(
                                            GenerateEqual(right, Expression.Constant(null, right.Type)), 
                                            this.GenerateComparisonExpression(left, right, op)));
                        } 
 
                    case ExpressionConstants.KeywordLessThan:
                        // (right != null) && ((left == null) || Compare(left, right) < 0) 
                        if (right == WebUtil.NullLiteral)
                        {
                            return Expression.Constant(false, typeof(bool));
                        } 
                        else if (left == WebUtil.NullLiteral)
                        { 
                            return GenerateNotEqual(right, Expression.Constant(null, right.Type)); 
                        }
                        else 
                        {
                            return GenerateLogicalAnd(
                                        GenerateNotEqual(right, Expression.Constant(null, left.Type)),
                                        GenerateLogicalOr( 
                                            GenerateEqual(left, Expression.Constant(null, right.Type)),
                                            this.GenerateComparisonExpression(left, right, op))); 
                        } 

                    default: 
                        // For now only < and > are supported as we use this only from $skiptoken
                        throw ParseError(
                            Strings.RequestQueryParser_NullOperatorUnsupported(op.Text, op.Position, this.lexer.ExpressionText));
                } 
            }
 
            ///  
            /// Given left and right hand side expressions, generates a comparison expression based
            /// on the given comparison token 
            /// 
            /// Left hand side expression
            /// Right hand side expression
            /// Comparison operator 
            /// Resulting comparison expression
            private Expression GenerateComparisonExpression(Expression left, Expression right, Token op) 
            { 
                bool equality = op.IsEqualityOperator;
                if (equality && !left.Type.IsValueType && !right.Type.IsValueType) 
                {
                    if (left.Type != right.Type)
                    {
                        if (WebUtil.IsNullConstant(left)) 
                        {
                            left = Expression.Constant(null, right.Type); 
                        } 
                        else if (WebUtil.IsNullConstant(right))
                        { 
                            right = Expression.Constant(null, left.Type);
                        }
                        else if (left.Type.IsAssignableFrom(right.Type))
                        { 
                            right = Expression.Convert(right, left.Type);
                        } 
                        else if (right.Type.IsAssignableFrom(left.Type)) 
                        {
                            left = Expression.Convert(left, right.Type); 
                        }
                        else
                        {
                            throw ExpressionParser.IncompatibleOperandsError(op.Text, left, right, op.Position); 
                        }
                    } 
                } 
                else if (left == WebUtil.NullLiteral || right == WebUtil.NullLiteral)
                { 
                    if (!equality)
                    {
                        throw ParseError(
                            Strings.RequestQueryParser_NullOperatorUnsupported(op.Text, op.Position, this.lexer.ExpressionText)); 
                    }
 
                    // Because we don't have an explicit "is null" check, literal comparisons 
                    // to null are special.
                    if (!WebUtil.TypeAllowsNull(left.Type)) 
                    {
                        left = Expression.Convert(left, typeof(Nullable<>).MakeGenericType(left.Type));
                    }
                    else if (!WebUtil.TypeAllowsNull(right.Type)) 
                    {
                        right = Expression.Convert(right, typeof(Nullable<>).MakeGenericType(right.Type)); 
                    } 
                }
                else 
                {
                    // Enums should be checked here for promotion when supported, but they aren't in this version.
                    Debug.Assert(!IsEnumType(left.Type), "!IsEnumType(left.Type)");
                    Debug.Assert(!IsEnumType(right.Type), "!IsEnumType(right.Type)"); 

                    Type signatures = equality ? typeof(OperationSignatures.IEqualitySignatures) : typeof(OperationSignatures.IRelationalSignatures); 
                    this.CheckAndPromoteOperands(signatures, op.Text, ref left, ref right, op.Position); 
                }
 
                Debug.Assert(op.Id == TokenId.Identifier, "op.id == TokenId.Identifier");
                MethodInfo comparisonMethodInfo = null;
                if (!equality)
                { 
                    if (left.Type == typeof(string))
                    { 
                        comparisonMethodInfo = StringCompareMethodInfo; 
                    }
                    else 
                    if (left.Type == typeof(bool))
                    {
                        comparisonMethodInfo = BoolCompareMethodInfo;
                    } 
                    else if (left.Type == typeof(bool?))
                    { 
                        comparisonMethodInfo = BoolCompareMethodInfoNullable; 
                    }
                    else 
                    if (left.Type == typeof(Guid))
                    {
                        comparisonMethodInfo = GuidCompareMethodInfo;
                    } 
                    else
                    if (left.Type == typeof(Guid?)) 
                    { 
                        comparisonMethodInfo = GuidCompareMethodInfoNullable;
                    } 
                }

                switch (op.Text)
                { 
                    case ExpressionConstants.KeywordEqual:
                        left = GenerateEqual(left, right); 
                        break; 
                    case ExpressionConstants.KeywordNotEqual:
                        left = GenerateNotEqual(left, right); 
                        break;
                    case ExpressionConstants.KeywordGreaterThan:
                        left = GenerateGreaterThan(left, right, comparisonMethodInfo);
                        break; 
                    case ExpressionConstants.KeywordGreaterThanOrEqual:
                        left = GenerateGreaterThanEqual(left, right, comparisonMethodInfo); 
                        break; 
                    case ExpressionConstants.KeywordLessThan:
                        left = GenerateLessThan(left, right, comparisonMethodInfo); 
                        break;
                    case ExpressionConstants.KeywordLessThanOrEqual:
                        left = GenerateLessThanEqual(left, right, comparisonMethodInfo);
                        break; 
                }
 
                return left; 
            }
 
            /// Handles +, -, & operators (& for string concat, not supported).
            /// The parsed expression.
            private Expression ParseAdditive()
            { 
                this.RecurseEnter();
                Expression left = this.ParseMultiplicative(); 
                while (this.CurrentToken.IdentifierIs(ExpressionConstants.KeywordAdd) || 
                    this.CurrentToken.IdentifierIs(ExpressionConstants.KeywordSub))
                { 
                    Token op = this.CurrentToken;
                    this.lexer.NextToken();
                    Expression right = this.ParseMultiplicative();
                    if (op.IdentifierIs(ExpressionConstants.KeywordAdd)) 
                    {
                        this.CheckAndPromoteOperands(typeof(OperationSignatures.IAddSignatures), op.Text, ref left, ref right, op.Position); 
                        left = GenerateAdd(left, right); 
                    }
                    else 
                    {
                        Debug.Assert(ExpressionParser.TokenIdentifierIs(op, ExpressionConstants.KeywordSub), "ExpressionParser.TokenIdentifierIs(op, ExpressionConstants.KeywordSub)");
                        this.CheckAndPromoteOperands(typeof(OperationSignatures.ISubtractSignatures), op.Text, ref left, ref right, op.Position);
                        left = GenerateSubtract(left, right); 
                    }
                } 
 
                this.RecurseLeave();
                return left; 
            }

            /// Handles mul, div, mod operators.
            /// The parsed expression. 
            private Expression ParseMultiplicative()
            { 
                this.RecurseEnter(); 
                Expression left = this.ParseUnary();
                while (this.CurrentToken.IdentifierIs(ExpressionConstants.KeywordMultiply) || 
                    this.CurrentToken.IdentifierIs(ExpressionConstants.KeywordDivide) ||
                    this.CurrentToken.IdentifierIs(ExpressionConstants.KeywordModulo))
                {
                    Token op = this.CurrentToken; 
                    this.lexer.NextToken();
                    Expression right = this.ParseUnary(); 
                    this.CheckAndPromoteOperands(typeof(OperationSignatures.IArithmeticSignatures), op.Text, ref left, ref right, op.Position); 
                    if (op.IdentifierIs(ExpressionConstants.KeywordMultiply))
                    { 
                        left = GenerateMultiply(left, right);
                    }
                    else if (op.IdentifierIs(ExpressionConstants.KeywordDivide))
                    { 
                        left = GenerateDivide(left, right);
                    } 
                    else 
                    {
                        Debug.Assert(op.IdentifierIs(ExpressionConstants.KeywordModulo), "op.IdentifierIs(ExpressionConstants.KeywordModulo)"); 
                        left = GenerateModulo(left, right);
                    }
                }
 
                this.RecurseLeave();
                return left; 
            } 

            /// Handles -, not unary operators. 
            /// The parsed expression.
            private Expression ParseUnary()
            {
                this.RecurseEnter(); 
                if (this.CurrentToken.Id == TokenId.Minus || this.CurrentToken.IdentifierIs(ExpressionConstants.KeywordNot))
                { 
                    Token op = this.CurrentToken; 
                    this.lexer.NextToken();
                    if (op.Id == TokenId.Minus && (ExpressionLexer.IsNumeric(this.CurrentToken.Id))) 
                    {
                        Token numberLiteral = this.CurrentToken;
                        numberLiteral.Text = "-" + numberLiteral.Text;
                        numberLiteral.Position = op.Position; 
                        this.CurrentToken = numberLiteral;
                        this.RecurseLeave(); 
                        return this.ParsePrimary(); 
                    }
 
                    Expression expr = this.ParseUnary();
                    if (op.Id == TokenId.Minus)
                    {
                        this.CheckAndPromoteOperand(typeof(OperationSignatures.INegationSignatures), op.Text, ref expr, op.Position); 
                        expr = GenerateNegate(expr);
                    } 
                    else 
                    {
                        this.CheckAndPromoteOperand(typeof(OperationSignatures.INotSignatures), op.Text, ref expr, op.Position); 
                        expr = GenerateNot(expr);
                    }

                    this.RecurseLeave(); 
                    return expr;
                } 
 
                this.RecurseLeave();
                return this.ParsePrimary(); 
            }

            /// Handles primary expressions.
            /// The parsed expression. 
            private Expression ParsePrimary()
            { 
                this.RecurseEnter(); 
                Expression expr = this.ParsePrimaryStart(this.lexer);
                while (true) 
                {
                    if (this.CurrentToken.Id == TokenId.Slash)
                    {
                        this.lexer.NextToken(); 
                        expr = this.ParseMemberAccess(expr);
                    } 
                    else 
                    {
                        break; 
                    }
                }

                this.RecurseLeave(); 
                return expr;
            } 
 
            /// Handles the start of primary expressions.
            /// Lexer to use for reading tokens 
            /// The parsed expression.
            private Expression ParsePrimaryStart(ExpressionLexer l)
            {
                switch (l.CurrentToken.Id) 
                {
                    case TokenId.BooleanLiteral: 
                        return this.ParseTypedLiteral(typeof(bool), XmlConstants.EdmBooleanTypeName, l); 
                    case TokenId.DateTimeLiteral:
                        return this.ParseTypedLiteral(typeof(DateTime), XmlConstants.EdmDateTimeTypeName, l); 
                    case TokenId.DecimalLiteral:
                        return this.ParseTypedLiteral(typeof(decimal), XmlConstants.EdmDecimalTypeName, l);
                    case TokenId.NullLiteral:
                        return ExpressionParser.ParseNullLiteral(l); 
                    case TokenId.Identifier:
                        Debug.Assert(Object.ReferenceEquals(this.lexer, l), "Lexer should be the member lexer"); 
                        return this.ParseIdentifier(); 
                    case TokenId.StringLiteral:
                        return this.ParseTypedLiteral(typeof(string), XmlConstants.EdmStringTypeName, l); 
                    case TokenId.Int64Literal:
                        return this.ParseTypedLiteral(typeof(Int64), XmlConstants.EdmInt64TypeName, l);
                    case TokenId.IntegerLiteral:
                        return this.ParseTypedLiteral(typeof(Int32), XmlConstants.EdmInt32TypeName, l); 
                    case TokenId.DoubleLiteral:
                        return this.ParseTypedLiteral(typeof(double), XmlConstants.EdmDoubleTypeName, l); 
                    case TokenId.SingleLiteral: 
                        return this.ParseTypedLiteral(typeof(Single), XmlConstants.EdmSingleTypeName, l);
                    case TokenId.GuidLiteral: 
                        return this.ParseTypedLiteral(typeof(Guid), XmlConstants.EdmGuidTypeName, l);
                    case TokenId.BinaryLiteral:
                        return this.ParseTypedLiteral(typeof(byte[]), XmlConstants.EdmBinaryTypeName, l);
                    case TokenId.OpenParen: 
                        Debug.Assert(Object.ReferenceEquals(this.lexer, l), "Lexer should be the member lexer");
                        return this.ParseParenExpression(); 
                    default: 
                        throw ParseError(Strings.RequestQueryParser_ExpressionExpected(l.CurrentToken.Position));
                } 
            }

            /// Handles parenthesized expressions.
            /// The parsed expression. 
            private Expression ParseParenExpression()
            { 
                if (this.CurrentToken.Id != TokenId.OpenParen) 
                {
                    throw ParseError(Strings.RequestQueryParser_OpenParenExpected(this.CurrentToken.Position)); 
                }

                this.lexer.NextToken();
                Expression e = this.ParseExpression(); 
                if (this.CurrentToken.Id != TokenId.CloseParen)
                { 
                    throw ParseError(Strings.RequestQueryParser_CloseParenOrOperatorExpected(this.CurrentToken.Position)); 
                }
 
                this.lexer.NextToken();
                return e;
            }
 
            /// Handles identifiers.
            /// The parsed expression. 
            private Expression ParseIdentifier() 
            {
                this.ValidateToken(TokenId.Identifier); 

                // An open paren here would indicate calling a method in regular C# syntax.
                bool identifierIsFunction = this.lexer.PeekNextToken().Id == TokenId.OpenParen;
                if (identifierIsFunction) 
                {
                    return this.ParseIdentifierAsFunction(); 
                } 
                else
                { 
                    this.currentSegmentInfo = new SegmentTypeInfo(this.typeForIt, this.setForIt, false);
                    return this.ParseMemberAccess(this.it);
                }
            } 

            /// Handles identifiers which have been recognized as functions. 
            /// The parsed expression. 
            private Expression ParseIdentifierAsFunction()
            { 
                FunctionDescription[] functionDescriptions;
                Token functionToken = this.CurrentToken;
                if (!functions.TryGetValue(functionToken.Text, out functionDescriptions))
                { 
                    throw ParseError(Strings.RequestQueryParser_UnknownFunction(functionToken.Text, functionToken.Position));
                } 
 
                this.lexer.NextToken();
                Expression[] originalArguments = this.ParseArgumentList(); 
                Expression[] arguments = this.nullPropagationRequired ? originalArguments : (Expression[])originalArguments.Clone();
                Expression candidateTypeArgument = arguments.Length > 1 ? arguments[1] :
                                                   arguments.Length > 0 ? arguments[0] :
                                                   null; 

                // check if the one of the parameters is of open type. If yes, then we need to invoke 
                // LateBoundMethods for this function otherwise not. 
                bool openParameters = false;
                if (!functionDescriptions[0].IsTypeCast && !functionDescriptions[0].IsTypeCheck) 
                {
                    foreach (Expression argument in arguments)
                    {
                        if (IsOpenPropertyExpression(argument)) 
                        {
                            openParameters = true; 
                            break; 
                        }
                    } 
                }

                Expression result = null;
                FunctionDescription function = null; 
                if (openParameters)
                { 
                    foreach (FunctionDescription functionDescription in functionDescriptions) 
                    {
                        if (functionDescription.ParameterTypes.Length == arguments.Length) 
                        {
                            function = functionDescription;
                            break;
                        } 
                    }
 
                    Expression[] openArguments = new Expression[arguments.Length]; 
                    for (int i = 0; i < openArguments.Length; i++)
                    { 
                        if (IsOpenPropertyExpression(arguments[i]))
                        {
                            openArguments[i] = arguments[i];
                        } 
                        else
                        { 
                            openArguments[i] = Expression.Convert(arguments[i], typeof(object)); 
                        }
                    } 

                    if (function == null)
                    {
                        string message = Strings.RequestQueryParser_NoApplicableFunction( 
                            functionToken.Text,
                            functionToken.Position, 
                            FunctionDescription.BuildSignatureList(functionToken.Text, functionDescriptions)); 
                        throw ParseError(message);
                    } 

                    result = function.InvokeOpenTypeMethod(openArguments);
                }
                else 
                {
                    function = this.FindBestFunction(functionDescriptions, ref arguments); 
                    if (function == null) 
                    {
                        string message = Strings.RequestQueryParser_NoApplicableFunction( 
                            functionToken.Text,
                            functionToken.Position,
                            FunctionDescription.BuildSignatureList(functionToken.Text, functionDescriptions));
                        throw ParseError(message); 
                    }
 
                    // Special case for null propagation - we never strip nullability from expressions. 
                    if (this.nullPropagationRequired && function.IsTypeCast)
                    { 
                        Expression typeExpression = arguments[arguments.Length - 1];
                        Debug.Assert(typeExpression != null, "typeExpression != null -- otherwise function finding failed.");
                        if (typeExpression.Type == typeof(Type))
                        { 
                            Type castTargetType = (Type)((ConstantExpression)typeExpression).Value;
                            if (!WebUtil.TypeAllowsNull(castTargetType)) 
                            { 
                                arguments[arguments.Length - 1] = Expression.Constant(typeof(Nullable<>).MakeGenericType(castTargetType));
                            } 
                        }
                    }

                    Expression[] finalArguments; 
                    if (function.ConversionFunction == FunctionDescription.BinaryIsOfResourceType ||
                        function.ConversionFunction == FunctionDescription.BinaryCastResourceType) 
                    { 
                        finalArguments = new Expression[arguments.Length + 1];
                        for (int i = 0; i < arguments.Length; i++) 
                        {
                            finalArguments[i] = arguments[i];
                        }
 
                        finalArguments[arguments.Length] = Expression.Constant(IsOpenPropertyExpression(arguments[0]), typeof(bool));
                    } 
                    else 
                    {
                        finalArguments = arguments; 
                    }

                    result = function.ConversionFunction(this.it, finalArguments);
                } 

                if (this.nullPropagationRequired && !function.IsTypeCheck && !function.IsTypeCast) 
                { 
                    Debug.Assert(
                        originalArguments.Length == arguments.Length, 
                        "originalArguments.Length == arguments.Length -- arguments should not be added/removed");
                    for (int i = 0; i < originalArguments.Length; i++)
                    {
                        result = this.ConsiderNullPropagation(originalArguments[i], result); 
                    }
                } 
 
                // type casts change the type of the "current" item, reflect this in parser state
                if (function.IsTypeCast) 
                {
                    Debug.Assert(candidateTypeArgument != null, "Should have failed to bind to the function if arguments don't match");
                    Debug.Assert(candidateTypeArgument.Type == typeof(string), "First argument to 'cast' should have been a string");
                    Debug.Assert(candidateTypeArgument.NodeType == ExpressionType.Constant, "Non-constant in type name for a cast?"); 

                    this.currentSegmentInfo = new SegmentTypeInfo( 
                        WebUtil.TryResolveResourceType(this.provider, (string)((ConstantExpression)candidateTypeArgument).Value), 
                        this.currentSegmentInfo != null ? this.currentSegmentInfo.ResourceSet : this.setForIt,
                        this.currentSegmentInfo != null ? this.currentSegmentInfo.IsCollection : false); 
                }

                return result;
            } 

            /// Handles boolean literals. 
            /// The parsed expression. 
            private Expression ParseBooleanLiteral()
            { 
                Debug.Assert(this.CurrentToken.Id == TokenId.BooleanLiteral, "this.CurrentToken.Id == TokenId.BooleanLiteral");
                string originalText = this.CurrentToken.Text;
                this.lexer.NextToken();
                if (originalText == ExpressionConstants.KeywordTrue) 
                {
                    return trueLiteral; 
                } 
                else
                { 
                    Debug.Assert(originalText == ExpressionConstants.KeywordFalse, "originalText == ExpressionConstants.KeywordFalse");
                    return falseLiteral;
                }
            } 

            /// Handles typed literals. 
            /// Expected type to be parsed. 
            /// Expected type name.
            /// Lexer to use for reading tokens 
            /// The constants expression produced by building the given literal.
            private Expression ParseTypedLiteral(Type targetType, string targetTypeName, ExpressionLexer l)
            {
                object targetValue; 
                if (!WebConvert.TryKeyStringToPrimitive(l.CurrentToken.Text, targetType, out targetValue))
                { 
                    string message = Strings.RequestQueryParser_UnrecognizedLiteral(targetTypeName, l.CurrentToken.Text, l.CurrentToken.Position); 
                    throw ParseError(message);
                } 

                Expression result = this.CreateLiteral(targetValue, l.CurrentToken.Text);
                l.NextToken();
                return result; 
            }
 
            /// Handles member access. 
            /// Instance being accessed.
            /// The parsed expression. 
            private Expression ParseMemberAccess(Expression instance)
            {
                Debug.Assert(instance != null, "instance != null");
 
                Type type = instance.Type;
                int errorPos = this.lexer.Position; 
                string id = this.CurrentToken.GetIdentifier(); 
                this.lexer.NextToken();
 
                // Disallow the member access for a collection property.
                Debug.Assert(this.currentSegmentInfo != null, "Must have initialized current segment information.");
                if (this.currentSegmentInfo.IsCollection)
                { 
                    throw ParseError(Strings.RequestQueryParser_UnknownProperty(id, WebUtil.GetTypeName(type), errorPos));
                } 
 
                // An open paren here would indicate calling a method in regular C# syntax.
                ResourceProperty property = this.currentSegmentInfo.ResourceType == null ? 
                                                null : // null means the current segment was already an open type
                                                this.currentSegmentInfo.ResourceType.TryResolvePropertyName(id);

                ResourceSetWrapper container = this.currentSegmentInfo.ResourceSet == null || property == null || property.TypeKind != ResourceTypeKind.EntityType ? 
                                    null :
                                    this.provider.GetContainer(this.currentSegmentInfo.ResourceSet, this.currentSegmentInfo.ResourceType, property); 
 
                if (property != null)
                { 
                    if (property.TypeKind == ResourceTypeKind.EntityType && container == null)
                    {
                        throw DataServiceException.CreateBadRequestError(Strings.BadRequest_InvalidPropertyNameSpecified(id, this.currentSegmentInfo.ResourceType.FullName));
                    } 

                    // We have a strongly-type property. 
                    Expression propertyAccess; 
                    if (property.CanReflectOnInstanceTypeProperty)
                    { 
                        propertyAccess = Expression.Property(instance, this.currentSegmentInfo.ResourceType.GetPropertyInfo(property));
                    }
                    else
                    { 
                        // object DataServiceProviderMethods.GetValue(object, ResourceProperty)
                        propertyAccess = Expression.Call( 
                                            null, /*instance*/ 
                                            DataServiceProviderMethods.GetValueMethodInfo,
                                            instance, 
                                            Expression.Constant(property));
                        propertyAccess = Expression.Convert(propertyAccess, property.Type);
                    }
 
                    Expression result = this.ConsiderNullPropagation(instance, propertyAccess);
                    if (container != null) 
                    { 
                        bool singleResult = property.Kind == ResourcePropertyKind.ResourceReference;
                        DataServiceConfiguration.CheckResourceRightsForRead(container, singleResult); 
                        Expression filter = DataServiceConfiguration.ComposeQueryInterceptors(this.service, container);
                        if (filter != null)
                        {
                            // We did null propagation for accessing the property, but we may also need 
                            // to do null propagation on the property value itself (otherwise the interception
                            // lambda needs to check the argument for null, which is probably unexpected). 
                            result = RequestQueryProcessor.ComposePropertyNavigation( 
                                result, (LambdaExpression)filter, this.provider.NullPropagationRequired);
                        } 
                    }

                    this.currentSegmentInfo = new SegmentTypeInfo(
                                    property.ResourceType, 
                                    container,
                                    property.Kind == ResourcePropertyKind.ResourceSetReference); 
                    return result; 
                }
                else 
                {
                    ResourceType resourceType = this.currentSegmentInfo.ResourceType;
                    this.currentSegmentInfo = new SegmentTypeInfo(null, null, false);
 
                    // Open types can have any members inside them
                    if (resourceType == null || resourceType.IsOpenType) 
                    { 
                        // object OpenTypeMethods.GetValue(object, string)
                        Expression call = 
                            Expression.Call(null /* instance */, OpenTypeMethods.GetValueOpenPropertyMethodInfo, instance, Expression.Constant(id));
                        return this.ConsiderNullPropagation(instance, call);
                    }
                    else 
                    {
                        throw ParseError(Strings.RequestQueryParser_UnknownProperty(id, WebUtil.GetTypeName(type), errorPos)); 
                    } 
                }
            } 

            /// Handles argument lists.
            /// The parsed expressions.
            private Expression[] ParseArgumentList() 
            {
                if (this.CurrentToken.Id != TokenId.OpenParen) 
                { 
                    throw ParseError(Strings.RequestQueryParser_OpenParenExpected(this.CurrentToken.Position));
                } 

                this.lexer.NextToken();
                Expression[] args = this.CurrentToken.Id != TokenId.CloseParen ? this.ParseArguments() : emptyExpressions;
                if (this.CurrentToken.Id != TokenId.CloseParen) 
                {
                    throw ParseError(Strings.RequestQueryParser_CloseParenOrCommaExpected(this.CurrentToken.Position)); 
                } 

                this.lexer.NextToken(); 
                return args;
            }

            /// Handles comma-separated arguments. 
            /// The parsed expressions.
            private Expression[] ParseArguments() 
            { 
                List argList = new List();
                while (true) 
                {
                    argList.Add(this.ParseExpression());
                    if (this.CurrentToken.Id != TokenId.Comma)
                    { 
                        break;
                    } 
 
                    this.lexer.NextToken();
                } 

                return argList.ToArray();
            }
 
            #endregion Parsing.
 
            /// Creates a constant expression with the specified literal. 
            /// Constant value.
            /// Value text. 
            /// The created expression.
            private Expression CreateLiteral(object value, string text)
            {
                // DEVNOTE([....]): 
                // The following code rely on Expression.Constant returning UNIQUE instances for every call to it
                // i.e., Expression.Constant(1) does not reference equals to Expression.Constant(1) 
                ConstantExpression expr = Expression.Constant(value); 
                this.literals.Add(expr, text);
                return expr; 
            }

            /// Finds the best fitting function for the specified arguments.
            /// Functions to consider. 
            /// Arguments; if a best function is found, promoted arguments.
            /// The best fitting function; null if none found or ambiguous. 
            private FunctionDescription FindBestFunction(FunctionDescription[] functions, ref Expression[] arguments) 
            {
                Debug.Assert(functions != null, "functions != null"); 
                List applicableFunctions = new List(functions.Length);
                List applicablePromotedArguments = new List(functions.Length);

                // Build a list of applicable functions (and cache their promoted arguments). 
                foreach (FunctionDescription candidate in functions)
                { 
                    if (candidate.ParameterTypes.Length != arguments.Length) 
                    {
                        continue; 
                    }

                    Expression[] promotedArguments = new Expression[arguments.Length];
                    bool argumentsMatch = true; 
                    for (int i = 0; i < candidate.ParameterTypes.Length; i++)
                    { 
                        promotedArguments[i] = this.PromoteExpression(arguments[i], candidate.ParameterTypes[i], true); 
                        if (promotedArguments[i] == null)
                        { 
                            argumentsMatch = false;
                            break;
                        }
                    } 

                    if (argumentsMatch) 
                    { 
                        applicableFunctions.Add(candidate);
                        applicablePromotedArguments.Add(promotedArguments); 
                    }
                }

                // Return the best applicable function. 
                if (applicableFunctions.Count == 0)
                { 
                    // No matching function. 
                    return null;
                } 
                else if (applicableFunctions.Count == 1)
                {
                    arguments = applicablePromotedArguments[0];
                    return applicableFunctions[0]; 
                }
                else 
                { 
                    // Find a single function which is better than all others.
                    int bestFunctionIndex = -1; 
                    for (int i = 0; i < applicableFunctions.Count; i++)
                    {
                        bool betterThanAllOthers = true;
                        for (int j = 0; j < applicableFunctions.Count; j++) 
                        {
                            if (i != j && IsBetterThan(arguments, applicableFunctions[j].ParameterTypes, applicableFunctions[i].ParameterTypes)) 
                            { 
                                betterThanAllOthers = false;
                                break; 
                            }
                        }

                        if (betterThanAllOthers) 
                        {
                            if (bestFunctionIndex == -1) 
                            { 
                                bestFunctionIndex = i;
                            } 
                            else
                            {
                                // Ambiguous.
                                return null; 
                            }
                        } 
                    } 

                    if (bestFunctionIndex == -1) 
                    {
                        return null;
                    }
 
                    arguments = applicablePromotedArguments[bestFunctionIndex];
                    return applicableFunctions[bestFunctionIndex]; 
                } 
            }
 
            /// Rewrites an expression to propagate null values if necessary.
            /// Expression to check for null.
            /// Expression to yield if  does not yield null.
            /// The possibly rewriteen . 
            private Expression ConsiderNullPropagation(Expression element, Expression notNullExpression)
            { 
                if (!this.nullPropagationRequired || element == this.it || !WebUtil.TypeAllowsNull(element.Type)) 
                {
                    return notNullExpression; 
                }

                // Tiny optimization: remove the check on constants which are known not to be null.
                // Otherwise every string literal propagates out, which is correct but unnecessarily messy. 
                if (element is ConstantExpression && element != WebUtil.NullLiteral)
                { 
                    return notNullExpression; 
                }
 
                // ifTrue and ifFalse expressions must match exactly. We need to ensure that the 'false'
                // side is nullable, and the 'true' side is a null of the correct type.
                Expression test = Expression.Equal(element, Expression.Constant(null, element.Type));
                Expression falseIf = notNullExpression; 
                if (!WebUtil.TypeAllowsNull(falseIf.Type))
                { 
                    falseIf = Expression.Convert(falseIf, typeof(Nullable<>).MakeGenericType(falseIf.Type)); 
                }
 
                Expression trueIf = Expression.Constant(null, falseIf.Type);
                return Expression.Condition(test, trueIf, falseIf);
            }
 
            /// Checks that the operand (possibly promoted) is valid for the specified operation.
            /// Type with signatures to match. 
            /// Name of operation for error reporting. 
            /// Expression for operand.
            /// Position for error reporting. 
            private void CheckAndPromoteOperand(Type signatures, string operationName, ref Expression expr, int errorPos)
            {
                Debug.Assert(signatures != null, "signatures != null");
                Debug.Assert(operationName != null, "operationName != null"); 
                Expression[] args = new Expression[] { expr };
                MethodBase method; 
                if (this.FindMethod(signatures, "F", args, out method) != 1) 
                {
                    throw ParseError(Strings.RequestQueryParser_IncompatibleOperand(operationName, WebUtil.GetTypeName(args[0].Type), errorPos)); 
                }

                expr = args[0];
            } 

            /// Checks that the operands (possibly promoted) are valid for the specified operation. 
            /// Type with signatures to match. 
            /// Name of operation for error reporting.
            /// Expression for left operand. 
            /// Expression for right operand.
            /// Position for error reporting.
            private void CheckAndPromoteOperands(Type signatures, string operationName, ref Expression left, ref Expression right, int errorPos)
            { 
                Expression[] args = new Expression[] { left, right };
                MethodBase method; 
                if (this.FindMethod(signatures, "F", args, out method) != 1) 
                {
                    throw ExpressionParser.IncompatibleOperandsError(operationName, left, right, errorPos); 
                }

                left = args[0];
                right = args[1]; 
            }
 
            /// Finds the named method in the specifid type. 
            /// Type to look in.
            /// Name of method to look for. 
            /// Arguments to method.
            /// Best method found.
            /// Number of matching methods.
            private int FindMethod(Type type, string methodName, Expression[] args, out MethodBase method) 
            {
                BindingFlags flags = BindingFlags.Public | BindingFlags.DeclaredOnly | BindingFlags.Static | BindingFlags.Instance; 
                foreach (Type t in SelfAndBaseTypes(type)) 
                {
                    MemberInfo[] members = t.FindMembers(MemberTypes.Method, flags, Type.FilterName, methodName); 
                    int count = this.FindBestMethod(members.Cast(), args, out method);
                    if (count != 0)
                    {
                        return count; 
                    }
                } 
 
                method = null;
                return 0; 
            }

            /// Finds all applicable methods from the specified enumeration that match the arguments.
            /// Enumerable object of candidate methods. 
            /// Argument expressions.
            /// Methods that apply to the specified arguments. 
            private MethodData[] FindApplicableMethods(IEnumerable methods, Expression[] args) 
            {
                List result = new List(); 
                foreach (MethodBase method in methods)
                {
                    MethodData methodData = new MethodData(method, method.GetParameters());
                    if (this.IsApplicable(methodData, args)) 
                    {
                        result.Add(methodData); 
                    } 
                }
 
                return result.ToArray();
            }

            /// Finds the best methods for the specified arguments given a candidate method enumeration. 
            /// Enumerable object for candidate methods.
            /// Argument expressions to match. 
            /// Best matched method. 
            /// The number of "best match" methods.
            private int FindBestMethod(IEnumerable methods, Expression[] args, out MethodBase method) 
            {
                MethodData[] applicable = this.FindApplicableMethods(methods, args);
                if (applicable.Length > 1)
                { 
                    applicable = FindBestApplicableMethods(applicable, args);
                } 
 
                int result = applicable.Length;
                method = null; 
                if (applicable.Length == 1)
                {
                    // If we started off with all non-OpenType expressions and end with all-OpenType
                    // expressions, we've been too aggresive - the transition from non-open-types 
                    // to open types should initially happen only as a result of accessing open properties.
                    MethodData md = applicable[0]; 
                    bool originalArgsDefined = true; 
                    bool promotedArgsOpen = true;
                    for (int i = 0; i < args.Length; i++) 
                    {
                        originalArgsDefined = originalArgsDefined && !IsOpenPropertyExpression(args[i]);
                        promotedArgsOpen = promotedArgsOpen && md.Parameters[i].ParameterType == typeof(object);
                        args[i] = md.Args[i]; 
                    }
 
                    method = (originalArgsDefined && promotedArgsOpen) ? null : md.MethodBase; 
                    result = (method == null) ? 0 : 1;
                } 
                else if (applicable.Length > 1)
                {
                    // We may have the case for operators (which C# doesn't) in which we have a nullable operand
                    // and a non-nullable operand. We choose to convert the one non-null operand to nullable in that 
                    // case (the binary expression will lift to null).
                    if (args.Length == 2 && applicable.Length == 2 && 
                        GetNonNullableType(applicable[0].Parameters[0].ParameterType) == 
                        GetNonNullableType(applicable[1].Parameters[0].ParameterType))
                    { 
                        MethodData nullableMethod =
                            WebUtil.TypeAllowsNull(applicable[0].Parameters[0].ParameterType) ?
                            applicable[0] :
                            applicable[1]; 
                        args[0] = nullableMethod.Args[0];
                        args[1] = nullableMethod.Args[1]; 
                        return this.FindBestMethod(methods, args, out method); 
                    }
                } 

                return result;
            }
 
            /// Checks whether the specified method is applicable given the argument expressions.
            /// Method to check. 
            /// Argument expressions. 
            /// true if the method is applicable; false otherwise.
            private bool IsApplicable(MethodData method, Expression[] args) 
            {
                if (method.Parameters.Length != args.Length)
                {
                    return false; 
                }
 
                Expression[] promotedArgs = new Expression[args.Length]; 
                for (int i = 0; i < args.Length; i++)
                { 
                    ParameterInfo pi = method.Parameters[i];
                    Debug.Assert(!pi.IsOut, "!pi.IsOut");
                    Expression promoted = this.PromoteExpression(args[i], pi.ParameterType, false);
                    if (promoted == null) 
                    {
                        return false; 
                    } 

                    promotedArgs[i] = promoted; 
                }

                method.Args = promotedArgs;
                return true; 
            }
 
            /// Promotes the specified expression to the given type if necessary. 
            /// Expression to promote.
            /// Type to change expression to. 
            /// Whether an exact type is required; false implies a compatible type is OK.
            /// Expression with the promoted type.
            private Expression PromoteExpression(Expression expr, Type type, bool exact)
            { 
                Debug.Assert(expr != null, "expr != null");
                Debug.Assert(type != null, "type != null"); 
                if (expr.Type == type) 
                {
                    return expr; 
                }

                ConstantExpression ce = expr as ConstantExpression;
                if (ce != null) 
                {
                    if (ce == WebUtil.NullLiteral) 
                    { 
                        if (WebUtil.TypeAllowsNull(type))
                        { 
                            return Expression.Constant(null, type);
                        }
                    }
                    else 
                    {
                        string text; 
                        if (this.literals.TryGetValue(ce, out text)) 
                        {
                            Type target = GetNonNullableType(type); 
                            object value = null;
                            if (ce.Type == typeof(string) && (target == typeof(Type) || target == typeof(ResourceType)))
                            {
                                if (WebConvert.TryRemoveQuotes(ref text)) 
                                {
                                    ResourceType resourceType = WebUtil.TryResolveResourceType(this.provider, text); 
                                    if (resourceType != null) 
                                    {
                                        if (target == typeof(Type)) 
                                        {
                                            if (resourceType.CanReflectOnInstanceType == true)
                                            {
                                                value = resourceType.InstanceType; 
                                            }
                                        } 
                                        else 
                                        {
                                            if (resourceType.CanReflectOnInstanceType == false) 
                                            {
                                                value = resourceType;
                                            }
                                        } 
                                    }
                                } 
                            } 
                            else
                            { 
                                switch (Type.GetTypeCode(ce.Type))
                                {
                                    case TypeCode.Int32:
                                    case TypeCode.Int64: 
                                        value = ParseNumber(text, target);
                                        break; 
                                    case TypeCode.Double: 
                                        if (target == typeof(decimal))
                                        { 
                                            value = ParseNumber(text, target);
                                        }

                                        break; 
                                }
                            } 
 
                            if (value != null)
                            { 
                                return Expression.Constant(value, type);
                            }
                        }
                    } 
                }
 
                if (IsCompatibleWith(expr.Type, type)) 
                {
                    if (type.IsValueType || exact) 
                    {
                        return Expression.Convert(expr, type);
                    }
 
                    return expr;
                } 
 
                // Allow promotion from nullable to non-nullable by directly accessing underlying value.
                if (WebUtil.IsNullableType(expr.Type) && type.IsValueType) 
                {
                    Expression valueAccessExpression = Expression.Property(expr, "Value");
                    valueAccessExpression = this.PromoteExpression(valueAccessExpression, type, exact);
                    return valueAccessExpression; 
                }
 
                return null; 
            }
 
            /// Checks that the current token has the specified identifier.
            /// Identifier to check.
            /// true if the current token is an identifier with the specified text.
            private bool TokenIdentifierIs(string id) 
            {
                return this.CurrentToken.IdentifierIs(id); 
            } 

            /// Validates the current token is of the specified kind. 
            /// Expected token kind.
            private void ValidateToken(TokenId t)
            {
                if (this.CurrentToken.Id != t) 
                {
                    throw ParseError(Strings.RequestQueryParser_SyntaxError(this.CurrentToken.Position)); 
                } 
            }
 
            #region Recursion control.

            /// Marks the fact that a recursive method was entered, and checks that the depth is allowed.
            private void RecurseEnter() 
            {
                WebUtil.RecurseEnterQueryParser(RecursionLimit, ref this.recursionDepth); 
            } 

            /// Marks the fact that a recursive method is leaving. 
            private void RecurseLeave()
            {
                WebUtil.RecurseLeave(ref this.recursionDepth);
            } 

            #endregion Recursion control. 
 
            /// Use this class to encapsulate method information.
            [DebuggerDisplay("MethodData {methodBase}")] 
            private class MethodData
            {
                #region Private fields.
 
                /// Described method.
                private readonly MethodBase methodBase; 
 
                /// Parameters for method.
                private readonly ParameterInfo[] parameters; 

                /// Argument expressions.
                private Expression[] args;
 
                #endregion Private fields.
 
                #region Constructors. 

                /// Initializes a new  instance. 
                /// Described method
                /// Parameters for method.
                public MethodData(MethodBase method, ParameterInfo[] parameters)
                { 
                    this.methodBase = method;
                    this.parameters = parameters; 
                } 

                #endregion Constructors. 

                #region Properties.

                /// Argument expressions. 
                public Expression[] Args
                { 
                    get { return this.args; } 
                    set { this.args = value; }
                } 

                /// Described method.
                public MethodBase MethodBase
                { 
                    get { return this.methodBase; }
                } 
 
                /// Parameters for method.
                public ParameterInfo[] Parameters 
                {
                    get { return this.parameters; }
                }
 
                /// Enumeration of parameter types.
                public IEnumerable ParameterTypes 
                { 
                    get
                    { 
                        foreach (ParameterInfo parameter in this.Parameters)
                        {
                            yield return parameter.ParameterType;
                        } 
                    }
                } 
 
                #endregion Properties.
            } 

            /// 
            /// ResourceType and ResourceSet information for current segment.
            /// This is used only when parsing member access paths. 
            /// 
            private class SegmentTypeInfo 
            { 
                /// Constructor.
                /// Type for current segment. 
                /// Set for current segment.
                /// Does current segment property refer to a collection.
                public SegmentTypeInfo(ResourceType resourceType, ResourceSetWrapper resourceSet, bool isCollection)
                { 
                    this.ResourceType = resourceType;
                    this.ResourceSet = resourceSet; 
                    this.IsCollection = isCollection; 
                }
 
                /// Type for the current segment.
                public ResourceType ResourceType
                {
                    get; 
                    private set;
                } 
 
                /// Resource set for the current segment.
                public ResourceSetWrapper ResourceSet 
                {
                    get;
                    private set;
                } 

                /// Does the current segment property refer to a collection. 
                public bool IsCollection 
                {
                    get; 
                    private set;
                }
            }
        } 
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
//---------------------------------------------------------------------- 
// 
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//  
//      Provides a type to parse expressions in request queries.
//  
// 
// @owner  [....]
//--------------------------------------------------------------------- 

namespace System.Data.Services.Parsing
{
    #region Namespaces. 

    using System; 
    using System.Collections.Generic; 
    using System.Data.Services.Providers;
    using System.Diagnostics; 
    using System.Linq;
    using System.Linq.Expressions;
    using System.Reflection;
 
    #endregion Namespaces.
 
    ///  
    /// This class provides static methods to parse query options and compose
    /// them on an existing query. 
    /// 
    internal static class RequestQueryParser
    {
        #region Internal methods. 

        /// Sorts a query like a SQL ORDER BY clause does. 
        /// Service with data and configuration. 
        /// Original source for query.
        /// Ordering definition to compose. 
        /// The composed query.
        internal static IQueryable OrderBy(IDataService service, IQueryable source, OrderingInfo orderingInfo)
        {
            Debug.Assert(service != null, "service != null"); 
            Debug.Assert(source != null, "source != null");
            Debug.Assert(orderingInfo != null, "orderingInfo != null"); 
 
            Expression queryExpr = source.Expression;
            string methodAsc = "OrderBy"; 
            string methodDesc = "OrderByDescending";
            foreach (OrderingExpression o in orderingInfo.OrderingExpressions)
            {
                LambdaExpression selectorLambda = (LambdaExpression)o.Expression; 
                Type selectorType = selectorLambda.Body.Type;
                service.Provider.CheckIfOrderedType(selectorType); 
 
                queryExpr = Expression.Call(
                    typeof(Queryable), 
                    o.IsAscending ? methodAsc : methodDesc,
                    new Type[] { source.ElementType, selectorType },
                    queryExpr,
                    Expression.Quote(selectorLambda)); 

                methodAsc = "ThenBy"; 
                methodDesc = "ThenByDescending"; 
            }
 
            return source.Provider.CreateQuery(queryExpr);
        }

        /// Filters a query like a SQL WHERE clause does. 
        /// Service with data and configuration.
        /// Set for each item in the query if they are entities 
        /// Type for each item in the query in Astoria metadata terms 
        /// Original source for query.
        /// Predicate to compose. 
        /// The composed query.
        internal static IQueryable Where(IDataService service, ResourceSetWrapper setForIt, ResourceType typeForIt, IQueryable source, string predicate)
        {
            Debug.Assert(service != null, "service != null"); 
            Debug.Assert(typeForIt != null, "typeForIt != null");
            Debug.Assert(typeForIt.ResourceTypeKind != ResourceTypeKind.EntityType || setForIt != null, "setForIt cannot be null if typeForIt is an entity type."); 
            Debug.Assert(source != null, "source != null"); 
            Debug.Assert(predicate != null, "predicate != null");
 
            LambdaExpression lambda = ParseLambdaForWhere(service, setForIt, typeForIt, source.ElementType, predicate);
            return source.Provider.CreateQuery(
                Expression.Call(typeof(Queryable), "Where", new Type[] { source.ElementType }, source.Expression, Expression.Quote(lambda)));
        } 

        #endregion Internal methods. 
 
        #region Private methods.
 
        /// Parses a lambda expression.
        /// Service with data and configuration.
        /// Resource set for "it" contextual variable.
        /// Type for "it" contextual variable. 
        /// Actual (clr) element type for the sequence
        /// Expression to parse. 
        /// The parsed expression. 
        private static LambdaExpression ParseLambdaForWhere(IDataService service, ResourceSetWrapper setForIt, ResourceType typeForIt, Type queryElementType, string expression)
        { 
            Debug.Assert(service != null, "service != null");
            Debug.Assert(typeForIt != null, "typeForIt != null");
            Debug.Assert(typeForIt.ResourceTypeKind != ResourceTypeKind.EntityType || setForIt != null, "setForIt cannot be null if typeForIt is an entity type.");
            Debug.Assert(queryElementType != null, "queryElementType != null"); 
            Debug.Assert(expression != null, "expression != null");
            Debug.Assert(typeForIt.InstanceType == queryElementType, "typeForIt.InstanceType == queryElementType"); 
 
            ParameterExpression parameterForIt = Expression.Parameter(queryElementType, "it");
            ExpressionParser parser = new ExpressionParser(service, setForIt, typeForIt, parameterForIt, expression); 
            return Expression.Lambda(parser.ParseWhere(), parameterForIt);
        }

        #endregion Private methods. 

        /// Use this class to parse an expression in the Astoria URI format. 
        [DebuggerDisplay("ExpressionParser ({lexer.text})")] 
        internal class ExpressionParser
        { 
            #region Fields.

            /// Maximum recursion limit on deserializer.
            private const int RecursionLimit = 100; 

            /// A type that is not numeric. 
            private const int NumericTypeNotNumeric = 0; 

            /// A type that is a char, single, double or decimal. 
            private const int NumericTypeNotIntegral = 1;

            /// A type that is a signed integral.
            private const int NumericTypeSignedIntegral = 2; 

            /// A type that is an unsigned integral. 
            private const int NumericTypeUnsignedIntegral = 3; 

            /// Empty Expressions array. 
            private static readonly Expression[] emptyExpressions = new Expression[0];

            /// Constant for "true" literal.
            private static readonly ConstantExpression trueLiteral = Expression.Constant(true); 

            /// Constant for "false" literal. 
            private static readonly ConstantExpression falseLiteral = Expression.Constant(false); 

            /// Dictionary of system functions. 
            private static readonly Dictionary functions = FunctionDescription.CreateFunctions();

            /// Method info for string comparison
            private static readonly MethodInfo StringCompareMethodInfo = typeof(DataServiceProviderMethods) 
                                                                  .GetMethods(BindingFlags.Public | BindingFlags.Static)
                                                                  .Single(m => m.Name == "Compare" && m.GetParameters()[0].ParameterType == typeof(string)); 
 
            /// Method info for Bool comparison
            private static readonly MethodInfo BoolCompareMethodInfo = typeof(DataServiceProviderMethods) 
                                                                  .GetMethods(BindingFlags.Public | BindingFlags.Static)
                                                                  .Single(m => m.Name == "Compare" && m.GetParameters()[0].ParameterType == typeof(bool));

            /// Method info for Bool? comparison 
            private static readonly MethodInfo BoolCompareMethodInfoNullable = typeof(DataServiceProviderMethods)
                                                                  .GetMethods(BindingFlags.Public | BindingFlags.Static) 
                                                                  .Single(m => m.Name == "Compare" && m.GetParameters()[0].ParameterType == typeof(bool?)); 

            /// Method info for Guid comparison 
            private static readonly MethodInfo GuidCompareMethodInfo = typeof(DataServiceProviderMethods)
                                                                  .GetMethods(BindingFlags.Public | BindingFlags.Static)
                                                                  .Single(m => m.Name == "Compare" && m.GetParameters()[0].ParameterType == typeof(Guid));
 
            /// Method info for Guid? comparison
            private static readonly MethodInfo GuidCompareMethodInfoNullable = typeof(DataServiceProviderMethods) 
                                                                  .GetMethods(BindingFlags.Public | BindingFlags.Static) 
                                                                  .Single(m => m.Name == "Compare" && m.GetParameters()[0].ParameterType == typeof(Guid?));
 
            /// Method info for byte array comparison.
            private static readonly MethodInfo ByteArrayEqualMethod = typeof(ExpressionParser)
                                                                  .GetMethod("ByteArraysEqual", BindingFlags.NonPublic | BindingFlags.Static);
 
            /// Method info for byte array comparison.
            private static readonly MethodInfo ByteArrayNotEqualMethod = typeof(ExpressionParser) 
                                                                  .GetMethod("ByteArraysNotEqual", BindingFlags.NonPublic | BindingFlags.Static); 

            /// Provider of data and metadata. 
            private readonly DataServiceProviderWrapper provider;

            /// Service with data and configuration.
            private readonly IDataService service; 

            /// Resource set for "it" 
            private readonly ResourceSetWrapper setForIt; 

            /// Metadata type for "it" 
            private readonly ResourceType typeForIt;

            /// Literals.
            private Dictionary literals; 

            /// "it" contextual parameter. 
            private ParameterExpression it; 

            /// Expression lexer. 
            private ExpressionLexer lexer;

            /// Whether the expression tree should propagate nulls explicitly.
            private bool nullPropagationRequired; 

            /// Depth of recursion. 
            private int recursionDepth; 

            /// ResourceType and ResourceSet information for current segment. 
            private SegmentTypeInfo currentSegmentInfo;

            #endregion Fields.
 
            #region Constructors.
 
            /// Initializes a new . 
            /// Service with data and configuration.
            /// Resource set for "it" contextual variable 
            /// Type for "it" contextual variable
            /// Parameters for the current "it" context.
            /// Expression to parse.
            internal ExpressionParser(IDataService service, ResourceSetWrapper setForIt, ResourceType typeForIt, ParameterExpression parameterForIt, string expression) 
            {
                Debug.Assert(service != null, "service != null"); 
 
                // For Open types, we could potentially have typeForIt parameter set to null value,
                // However, we have decided not support ordering on Open properties which also implies 
                // that we can not have entity typed properties on Open types
                Debug.Assert(typeForIt != null, "typeForIt != null");

                Debug.Assert(expression != null, "expression != null"); 
                Debug.Assert(parameterForIt != null, "parameterForIt != null");
 
                this.service = service; 
                this.provider = service.Provider;
                this.nullPropagationRequired = this.provider.NullPropagationRequired; 
                this.literals = new Dictionary(ReferenceEqualityComparer.Instance);
                this.setForIt = setForIt;
                this.typeForIt = typeForIt;
                this.it = parameterForIt; 
                this.lexer = new ExpressionLexer(expression);
            } 
 
            #endregion Constructors.
 
            /// Current token being processed.
            private Token CurrentToken
            {
                get { return this.lexer.CurrentToken; } 
                set { this.lexer.CurrentToken = value; }
            } 
 
            /// Parses the text expression for a .Where method invocation.
            /// The parsed expression. 
            internal Expression ParseWhere()
            {
                int exprPos = this.lexer.Position;
                Expression expr = this.ParseExpression(); 

                expr = PrepareExpressionForWhere(expr); 
                if (expr.Type != typeof(bool)) 
                {
                    throw ParseError(Strings.RequestQueryParser_ExpressionTypeMismatch(WebUtil.GetTypeName(typeof(bool)), exprPos)); 
                }

                this.lexer.ValidateToken(TokenId.End);
                return expr; 
            }
 
            /// Makes the expression that is used as a filter corresponding to skip token. 
            /// Ordering expression.
            /// The provided skip token. 
            /// LambdaExpression corresponding to the skip token filter.
            internal LambdaExpression BuildSkipTokenFilter(OrderingInfo topLevelOrderingInfo, KeyInstance k)
            {
                ParameterExpression element = Expression.Parameter(this.typeForIt.InstanceType, "element"); 
                Expression lastCondition = Expression.Constant(true, typeof(bool));
                Expression lastMatch = Expression.Constant(false, typeof(bool)); 
 
                foreach (var v in WebUtil.Zip(topLevelOrderingInfo.OrderingExpressions, k.PositionalValues, (x, y) => new { Order = x, Value = y }))
                { 
                    Token comparisonExp = v.Order.IsAscending ? Token.GreaterThan : Token.LessThan;

                    Expression fixedLambda = System.Data.Services.Client.ParameterReplacerVisitor.Replace(
                                                    ((LambdaExpression)v.Order.Expression).Body, 
                                                    ((LambdaExpression)v.Order.Expression).Parameters[0],
                                                    element); 
 
                    Expression comparison = GenerateLogicalAnd(
                                                lastCondition, 
                                                this.GenerateNullAwareComparison(fixedLambda, (String)v.Value, comparisonExp));

                    lastMatch = GenerateLogicalOr(lastMatch, comparison);
 
                    lastCondition = GenerateLogicalAnd(
                                        lastCondition, 
                                        this.GenerateComparison(fixedLambda, (String)v.Value, Token.EqualsTo)); 
                }
 
                lastMatch = PrepareExpressionForWhere(lastMatch);

                Debug.Assert(lastMatch.Type == typeof(bool), "Skip token should generate boolean expression.");
 
                return Expression.Lambda(lastMatch, element);
            } 
 
            /// Parses the text expression for ordering.
            /// An enumeration of orderings. 
            internal IEnumerable ParseOrdering()
            {
                List orderings = new List();
                while (true) 
                {
                    Expression expr = this.ParseExpression(); 
                    bool ascending = true; 
                    if (this.TokenIdentifierIs(ExpressionConstants.KeywordAscending))
                    { 
                        this.lexer.NextToken();
                    }
                    else if (this.TokenIdentifierIs(ExpressionConstants.KeywordDescending))
                    { 
                        this.lexer.NextToken();
                        ascending = false; 
                    } 

                    orderings.Add(new OrderingExpression(expr, ascending)); 
                    if (this.CurrentToken.Id != TokenId.Comma)
                    {
                        break;
                    } 

                    this.lexer.NextToken(); 
                } 

                this.ValidateToken(TokenId.End); 
                return orderings;
            }

            /// Parse one of the literals of skip token. 
            /// Input literal.
            /// Object resulting from conversion of literal. 
            internal object ParseSkipTokenLiteral(String literal) 
            {
                ExpressionLexer l = new ExpressionLexer(literal); 
                Expression e = this.ParsePrimaryStart(l);
                if (e.NodeType != ExpressionType.Constant)
                {
                    throw new InvalidOperationException(Strings.RequsetQueryParser_ExpectingLiteralInSkipToken(literal)); 
                }
 
                return ((ConstantExpression)e).Value; 
            }
 
            /// Prepare the given expression for passing as a filter to Queryable.Where.
            /// Input expression.
            /// Expression converted to boolean expression.
            private static Expression PrepareExpressionForWhere(Expression expr) 
            {
                if (IsOpenPropertyExpression(expr)) 
                { 
                    expr = OpenTypeMethods.EqualExpression(expr, Expression.Constant(true, typeof(object)));
                    expr = Expression.Convert(expr, typeof(bool)); 
                }
                else if (WebUtil.IsNullConstant(expr))
                {
                    expr = falseLiteral; 
                }
                else if (expr.Type == typeof(bool?)) 
                { 
                    Expression test = Expression.Equal(expr, Expression.Constant(null, typeof(bool?)));
                    expr = Expression.Condition(test, falseLiteral, Expression.Property(expr, "Value")); 
                }

                return expr;
            } 

            /// Compares two byte arrays for equality. 
            /// First byte array.Second byte array. 
            /// true if the arrays are equal; false otherwise.
            private static bool ByteArraysEqual(byte[] b0, byte[] b1) 
            {
                if (b0 == b1)
                {
                    return true; 
                }
 
                if (b0 == null || b1 == null) 
                {
                    return false; 
                }

                if (b0.Length != b1.Length)
                { 
                    return false;
                } 
 
                for (int i = 0; i < b0.Length; i++)
                { 
                    if (b0[i] != b1[i])
                    {
                        return false;
                    } 
                }
 
                return true; 
            }
 
            /// Compares two byte arrays for equality.
            /// First byte array.Second byte array.
            /// true if the arrays are not equal; false otherwise.
            private static bool ByteArraysNotEqual(byte[] b0, byte[] b1) 
            {
                return !ByteArraysEqual(b0, b1); 
            } 

            /// Gets a non-nullable version of the specified type. 
            /// Type to get non-nullable version for.
            /// 
            ///  if type is a reference type or a
            /// non-nullable type; otherwise, the underlying value type. 
            /// 
            private static Type GetNonNullableType(Type type) 
            { 
                return Nullable.GetUnderlyingType(type) ?? type;
            } 

            /// Checks whether the specified type is a signed integral type.
            /// Type to check.
            /// true if  is a signed integral type; false otherwise. 
            private static bool IsSignedIntegralType(Type type)
            { 
                return GetNumericTypeKind(type) == NumericTypeSignedIntegral; 
            }
 
            /// Checks whether the specified type is an unsigned integral type.
            /// Type to check.
            /// true if  is an unsigned integral type; false otherwise.
            private static bool IsUnsignedIntegralType(Type type) 
            {
                return GetNumericTypeKind(type) == NumericTypeUnsignedIntegral; 
            } 

            /// Gets a flag for the numeric kind of type. 
            /// Type to get numeric kind for.
            /// 
            /// One of NumericTypeNotNumeric; NumericTypeNotIntegral if it's char,
            /// single, double or decimal; NumericTypeSignedIntegral, or NumericTypeUnsignedIntegral. 
            /// 
            private static int GetNumericTypeKind(Type type) 
            { 
                type = GetNonNullableType(type);
                Debug.Assert(!type.IsEnum, "!type.IsEnum"); 
                switch (Type.GetTypeCode(type))
                {
                    case TypeCode.Char:
                    case TypeCode.Single: 
                    case TypeCode.Double:
                    case TypeCode.Decimal: 
                        return NumericTypeNotIntegral; 
                    case TypeCode.SByte:
                    case TypeCode.Int16: 
                    case TypeCode.Int32:
                    case TypeCode.Int64:
                        return NumericTypeSignedIntegral;
                    case TypeCode.Byte: 
                        return NumericTypeUnsignedIntegral;
                    default: 
                        return NumericTypeNotNumeric; 
                }
            } 

            /// Checks whether type is a (possibly nullable) enumeration type.
            /// Type to check.
            /// true if type is an enumeration or a nullable enumeration; false otherwise. 
            private static bool IsEnumType(Type type)
            { 
                return GetNonNullableType(type).IsEnum; 
            }
 
            /// Returns an object that can enumerate the specified type and its supertypes.
            /// Type to based enumeration on.
            /// An object that can enumerate the specified type and its supertypes.
            private static IEnumerable SelfAndBaseTypes(Type type) 
            {
                if (type.IsInterface) 
                { 
                    List types = new List();
                    AddInterface(types, type); 
                    return types;
                }

                return SelfAndBaseClasses(type); 
            }
 
            /// Returns an object that can enumerate the specified type and its supertypes. 
            /// Type to based enumeration on.
            /// An object that can enumerate the specified type and its supertypes. 
            private static IEnumerable SelfAndBaseClasses(Type type)
            {
                while (type != null)
                { 
                    yield return type;
                    type = type.BaseType; 
                } 
            }
 
            /// Adds an interface type to a list of types, including inherited interfaces.
            /// Types list ot add to.
            /// Interface type to add.
            private static void AddInterface(List types, Type type) 
            {
                if (!types.Contains(type)) 
                { 
                    types.Add(type);
                    foreach (Type t in type.GetInterfaces()) 
                    {
                        AddInterface(types, t);
                    }
                } 
            }
 
            /// Finds the best applicable methods from the specified array that match the arguments. 
            /// Candidate methods.
            /// Argument expressions. 
            /// Best applicable methods.
            private static MethodData[] FindBestApplicableMethods(MethodData[] applicable, Expression[] args)
            {
                Debug.Assert(applicable != null, "applicable != null"); 

                List result = new List(); 
                foreach (MethodData method in applicable) 
                {
                    bool betterThanAllOthers = true; 
                    foreach (MethodData otherMethod in applicable)
                    {
                        if (otherMethod != method && IsBetterThan(args, otherMethod, method))
                        { 
                            betterThanAllOthers = false;
                            break; 
                        } 
                    }
 
                    if (betterThanAllOthers)
                    {
                        result.Add(method);
                    } 
                }
 
                return result.ToArray(); 
            }
 
            /// Parses the specified text into a number.
            /// Text to parse.
            /// Type to parse into.
            /// The parsed number. 
            private static object ParseNumber(string text, Type type)
            { 
                TypeCode tc = Type.GetTypeCode(GetNonNullableType(type)); 
                switch (tc)
                { 
                    case TypeCode.SByte:
                        sbyte sb;
                        if (sbyte.TryParse(text, out sb))
                        { 
                            return sb;
                        } 
 
                        break;
                    case TypeCode.Byte: 
                        byte b;
                        if (byte.TryParse(text, out b))
                        {
                            return b; 
                        }
 
                        break; 
                    case TypeCode.Int16:
                        short s; 
                        if (short.TryParse(text, out s))
                        {
                            return s;
                        } 

                        break; 
                    case TypeCode.Int32: 
                        int i;
                        if (int.TryParse(text, out i)) 
                        {
                            return i;
                        }
 
                        break;
                    case TypeCode.Int64: 
                        long l; 
                        if (long.TryParse(text, out l))
                        { 
                            return l;
                        }

                        break; 
                    case TypeCode.Single:
                        float f; 
                        if (float.TryParse(text, out f)) 
                        {
                            return f; 
                        }

                        break;
                    case TypeCode.Double: 
                        double d;
                        if (double.TryParse(text, out d)) 
                        { 
                            return d;
                        } 

                        break;
                    case TypeCode.Decimal:
                        decimal e; 
                        if (decimal.TryParse(text, out e))
                        { 
                            return e; 
                        }
 
                        break;
                }

                return null; 
            }
 
            /// Checks whether the source type is compatible with the value type. 
            /// Source type.
            /// Target type. 
            /// true if source can be used in place of target; false otherwise.
            private static bool IsCompatibleWith(Type source, Type target)
            {
                if (source == target) 
                {
                    return true; 
                } 

                if (!target.IsValueType) 
                {
                    return target.IsAssignableFrom(source);
                }
 
                Type sourceType = GetNonNullableType(source);
                Type targetType = GetNonNullableType(target); 
 
                //// This rule stops the parser from considering nullable types as incompatible
                //// with non-nullable types. We have however implemented this rule because we just 
                //// access underlying rules. C# requires an explicit .Value access, and EDM has no
                //// nullablity on types and (at the model level) implements null propagation.
                ////
                //// if (sourceType != source && targetType == target) 
                //// {
                ////     return false; 
                //// } 

                TypeCode sourceCode = sourceType.IsEnum ? TypeCode.Object : Type.GetTypeCode(sourceType); 
                TypeCode targetCode = targetType.IsEnum ? TypeCode.Object : Type.GetTypeCode(targetType);
                switch (sourceCode)
                {
                    case TypeCode.SByte: 
                        switch (targetCode)
                        { 
                            case TypeCode.SByte: 
                            case TypeCode.Int16:
                            case TypeCode.Int32: 
                            case TypeCode.Int64:
                            case TypeCode.Single:
                            case TypeCode.Double:
                            case TypeCode.Decimal: 
                                return true;
                        } 
 
                        break;
                    case TypeCode.Byte: 
                        switch (targetCode)
                        {
                            case TypeCode.Byte:
                            case TypeCode.Int16: 
                            case TypeCode.Int32:
                            case TypeCode.Int64: 
                            case TypeCode.Single: 
                            case TypeCode.Double:
                            case TypeCode.Decimal: 
                                return true;
                        }

                        break; 
                    case TypeCode.Int16:
                        switch (targetCode) 
                        { 
                            case TypeCode.Int16:
                            case TypeCode.Int32: 
                            case TypeCode.Int64:
                            case TypeCode.Single:
                            case TypeCode.Double:
                            case TypeCode.Decimal: 
                                return true;
                        } 
 
                        break;
                    case TypeCode.Int32: 
                        switch (targetCode)
                        {
                            case TypeCode.Int32:
                            case TypeCode.Int64: 
                            case TypeCode.Single:
                            case TypeCode.Double: 
                            case TypeCode.Decimal: 
                                return true;
                        } 

                        break;
                    case TypeCode.Int64:
                        switch (targetCode) 
                        {
                            case TypeCode.Int64: 
                            case TypeCode.Single: 
                            case TypeCode.Double:
                            case TypeCode.Decimal: 
                                return true;
                        }

                        break; 
                    case TypeCode.Single:
                        switch (targetCode) 
                        { 
                            case TypeCode.Single:
                            case TypeCode.Double: 
                                return true;
                        }

                        break; 
                    default:
                        if (sourceType == targetType) 
                        { 
                            return true;
                        } 

                        break;
                }
 
                // Anything can be converted to something that's *exactly* an object.
                if (target == typeof(object)) 
                { 
                    return true;
                } 

                return false;
            }
 
            /// 
            /// Checks whether one type list is a better fit than other for the 
            /// specified expressions. 
            /// 
            /// Expressions for arguments. 
            /// First type list to check.
            /// Second type list to check.
            /// 
            /// true if  has better parameter matching than . 
            /// 
            private static bool IsBetterThan(Expression[] args, IEnumerable firstCandidate, IEnumerable secondCandidate) 
            { 
                bool better = false;
 
                using (IEnumerator first = firstCandidate.GetEnumerator())
                using (IEnumerator second = secondCandidate.GetEnumerator())
                {
                    for (int i = 0; i < args.Length; i++) 
                    {
                        first.MoveNext(); 
                        second.MoveNext(); 
                        int c = CompareConversions(args[i].Type, first.Current, second.Current);
                        if (c < 0) 
                        {
                            return false;
                        }
                        else if (c > 0) 
                        {
                            better = true; 
                        } 
                    }
                } 

                return better;
            }
 
            /// 
            /// Checks whether one method is a better fit than other for the 
            /// specified expressions. 
            /// 
            /// Expressions for arguments. 
            /// First method to check.
            /// Second method to check.
            /// 
            /// true if  has better parameter matching than . 
            /// 
            private static bool IsBetterThan(Expression[] args, MethodData m1, MethodData m2) 
            { 
                Debug.Assert(args != null, "args != null");
                Debug.Assert(m1 != null, "m1 != null"); 
                Debug.Assert(m2 != null, "m2 != null");
                return IsBetterThan(args, m1.ParameterTypes, m2.ParameterTypes);
            }
 
            /// Checks which conversion is better.
            /// Source type. 
            /// First candidate type to convert to. 
            /// Second candidate type to convert to.
            ///  
            /// Return 1 if s -> t1 is a better conversion than s -> t2
            /// Return -1 if s -> t2 is a better conversion than s -> t1
            /// Return 0 if neither conversion is better
            ///  
            private static int CompareConversions(Type source, Type targetA, Type targetB)
            { 
                // If both types are exactly the same, there is no preference. 
                if (targetA == targetB)
                { 
                    return 0;
                }

                // Look for exact matches. 
                if (source == targetA)
                { 
                    return 1; 
                }
                else if (source == targetB) 
                {
                    return -1;
                }
 
                // If one is compatible and the other is not, choose the compatible type.
                bool compatibleT1AndT2 = IsCompatibleWith(targetA, targetB); 
                bool compatibleT2AndT1 = IsCompatibleWith(targetB, targetA); 
                if (compatibleT1AndT2 && !compatibleT2AndT1)
                { 
                    return 1;
                }
                else if (compatibleT2AndT1 && !compatibleT1AndT2)
                { 
                    return -1;
                } 
 
                // Prefer to keep the original nullability.
                bool sourceNullable = WebUtil.IsNullableType(source); 
                bool typeNullableA = WebUtil.IsNullableType(targetA);
                bool typeNullableB = WebUtil.IsNullableType(targetB);
                if (sourceNullable == typeNullableA && sourceNullable != typeNullableB)
                { 
                    return 1;
                } 
                else if (sourceNullable != typeNullableA && sourceNullable == typeNullableB) 
                {
                    return -1; 
                }

                // Prefer signed to unsigned.
                if (IsSignedIntegralType(targetA) && IsUnsignedIntegralType(targetB)) 
                {
                    return 1; 
                } 
                else if (IsSignedIntegralType(targetB) && IsUnsignedIntegralType(targetA))
                { 
                    return -1;
                }

                // Prefer non-object to object. 
                if (targetA != typeof(object) && targetB == typeof(object))
                { 
                    return 1; 
                }
                else if (targetB != typeof(object) && targetA == typeof(object)) 
                {
                    return -1;
                }
 
                return 0;
            } 
 
            /// Generates an Equal expression.
            /// Left expression. 
            /// Right expression.
            /// The generated expression.
            private static Expression GenerateEqual(Expression left, Expression right)
            { 
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.EqualExpression(left, right); 
                }
 
                if (left.Type == typeof(byte[]))
                {
                    return Expression.Equal(left, right, false, ExpressionParser.ByteArrayEqualMethod);
                } 

                return Expression.Equal(left, right); 
            } 

            /// Generates a NotEqual expression. 
            /// Left expression.
            /// Right expression.
            /// The generated expression.
            private static Expression GenerateNotEqual(Expression left, Expression right) 
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right)) 
                { 
                    return OpenTypeMethods.NotEqualExpression(left, right);
                } 

                if (left.Type == typeof(byte[]))
                {
                    return Expression.NotEqual(left, right, false, ExpressionParser.ByteArrayNotEqualMethod); 
                }
 
                return Expression.NotEqual(left, right); 
            }
 
            /// Generates a GreaterThan comparison expression.
            /// Left expression.
            /// Right expression.
            /// MethodInfo for comparison method used for string, bool, guid types 
            /// The generated expression.
            private static Expression GenerateGreaterThan(Expression left, Expression right, MethodInfo comparisonMethodInfo) 
            { 
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.GreaterThanExpression(left, right);
                }

                if (comparisonMethodInfo != null) 
                {
                    left = Expression.Call(null, comparisonMethodInfo, left, right); 
                    right = Expression.Constant(0, typeof(int)); 
                }
 
                return Expression.GreaterThan(left, right);
            }

            /// Generates a GreaterThanOrEqual comparsion expression. 
            /// Left expression.
            /// Right expression. 
            /// MethodInfo for comparison method used for string, bool, guid types 
            /// The generated expression.
            private static Expression GenerateGreaterThanEqual(Expression left, Expression right, MethodInfo comparisonMethodInfo) 
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                {
                    return OpenTypeMethods.GreaterThanOrEqualExpression(left, right); 
                }
 
                if (comparisonMethodInfo != null) 
                {
                    left = Expression.Call(null, comparisonMethodInfo, left, right); 
                    right = Expression.Constant(0, typeof(int));
                }

                return Expression.GreaterThanOrEqual(left, right); 
            }
 
            /// Generates a LessThan comparsion expression. 
            /// Left expression.
            /// Right expression. 
            /// MethodInfo for comparison method used for string, bool, guid types
            /// The generated expression.
            private static Expression GenerateLessThan(Expression left, Expression right, MethodInfo comparisonMethodInfo)
            { 
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.LessThanExpression(left, right); 
                }
 
                if (comparisonMethodInfo != null)
                {
                    left = Expression.Call(null, comparisonMethodInfo, left, right);
                    right = Expression.Constant(0, typeof(int)); 
                }
 
                return Expression.LessThan(left, right); 
            }
 
            /// Generates a LessThanOrEqual comparsion expression.
            /// Left expression.
            /// Right expression.
            /// MethodInfo for comparison method used for string, bool, guid types 
            /// The generated expression.
            private static Expression GenerateLessThanEqual(Expression left, Expression right, MethodInfo comparisonMethodInfo) 
            { 
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.LessThanOrEqualExpression(left, right);
                }

                if (comparisonMethodInfo != null) 
                {
                    left = Expression.Call(null, comparisonMethodInfo, left, right); 
                    right = Expression.Constant(0, typeof(int)); 
                }
 
                return Expression.LessThanOrEqual(left, right);
            }

            ///  
            /// Compares 2 strings by ordinal, used to obtain MethodInfo for comparison operator expression parameter
            ///  
            /// Left Parameter 
            /// Right Parameter
            /// 0 for equality, -1 for left less than right, 1 for left greater than right 
            /// 
            /// Do not change the name of this function because LINQ to SQL is sensitive about the
            /// method name, so is EF probably.
            ///  
            private static int Compare(String left, String right)
            { 
                return Comparer.Default.Compare(left, right); 
            }
 
            /// 
            /// Compares 2 booleans with true greater than false, used to obtain MethodInfo for comparison operator expression parameter
            /// 
            /// Left Parameter 
            /// Right Parameter
            /// 0 for equality, -1 for left less than right, 1 for left greater than right 
            ///  
            /// Do not change the name of this function because LINQ to SQL is sensitive about the
            /// method name, so is EF probably. 
            /// 
            [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.MSInternal", "CA908:AvoidTypesThatRequireJitCompilationInPrecompiledAssemblies", Justification = "Need implementation")]
            private static int Compare(bool left, bool right)
            { 
                return Comparer.Default.Compare(left, right);
            } 
 
            /// 
            /// Compares 2 nullable booleans with true greater than false, used to obtain MethodInfo for comparison operator expression parameter 
            /// 
            /// Left Parameter
            /// Right Parameter
            /// 0 for equality, -1 for left less than right, 1 for left greater than right 
            /// 
            /// Do not change the name of this function because LINQ to SQL is sensitive about the 
            /// method name, so is EF probably. 
            /// 
            [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.MSInternal", "CA908:AvoidTypesThatRequireJitCompilationInPrecompiledAssemblies", Justification = "Need implementation")] 
            private static int Compare(bool? left, bool? right)
            {
                return Comparer.Default.Compare(left, right);
            } 

            ///  
            /// Compares 2 guids by byte order, used to obtain MethodInfo for comparison operator expression parameter 
            /// 
            /// Left Parameter 
            /// Right Parameter
            /// 0 for equality, -1 for left less than right, 1 for left greater than right
            /// 
            /// Do not change the name of this function because LINQ to SQL is sensitive about the 
            /// method name, so is EF probably.
            ///  
            [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.MSInternal", "CA908:AvoidTypesThatRequireJitCompilationInPrecompiledAssemblies", Justification = "Need implementation")] 
            private static int Compare(Guid left, Guid right)
            { 
                return Comparer.Default.Compare(left, right);
            }

            ///  
            /// Compares 2 nullable guids by byte order, used to obtain MethodInfo for comparison operator expression parameter
            ///  
            /// Left Parameter 
            /// Right Parameter
            /// 0 for equality, -1 for left less than right, 1 for left greater than right 
            /// 
            /// Do not change the name of this function because LINQ to SQL is sensitive about the
            /// method name, so is EF probably.
            ///  
            [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.MSInternal", "CA908:AvoidTypesThatRequireJitCompilationInPrecompiledAssemblies", Justification = "Need implementation")]
            private static int Compare(Guid? left, Guid? right) 
            { 
                return Comparer.Default.Compare(left, right);
            } 

            /// Generates an addition expression.
            /// Left expression.
            /// Right expression. 
            /// The generated expression.
            private static Expression GenerateAdd(Expression left, Expression right) 
            { 
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.AddExpression(left, right);
                }

                return Expression.Add(left, right); 
            }
 
            /// Generates a subtract expression. 
            /// Left expression.
            /// Right expression. 
            /// The generated expression.
            private static Expression GenerateSubtract(Expression left, Expression right)
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right)) 
                {
                    return OpenTypeMethods.SubtractExpression(left, right); 
                } 

                return Expression.Subtract(left, right); 
            }

            /// Generates a multiplication expression.
            /// Left expression. 
            /// Right expression.
            /// The generated expression. 
            private static Expression GenerateMultiply(Expression left, Expression right) 
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right)) 
                {
                    return OpenTypeMethods.MultiplyExpression(left, right);
                }
 
                return Expression.Multiply(left, right);
            } 
 
            /// Generates a negative of expression.
            /// Input expression. 
            /// The generated expression.
            private static Expression GenerateNegate(Expression expr)
            {
                if (IsOpenPropertyExpression(expr)) 
                {
                    return OpenTypeMethods.NegateExpression(expr); 
                } 

                return Expression.Negate(expr); 
            }

            /// Generates a not of expression.
            /// Input expression. 
            /// The generated expression.
            private static Expression GenerateNot(Expression expr) 
            { 
                if (IsOpenPropertyExpression(expr))
                { 
                    return OpenTypeMethods.NotExpression(expr);
                }

                if (expr.Type == typeof(bool) || expr.Type == typeof(Nullable)) 
                {
                    // Expression.Not will take numerics and apply '~' to them, thus the extra check here. 
                    return Expression.Not(expr); 
                }
                else 
                {
                    throw ParseError(Strings.RequestQueryParser_NotDoesNotSupportType(expr.Type));
                }
            } 

            /// Generates a divide expression. 
            /// Left expression. 
            /// Right expression.
            /// The generated expression. 
            private static Expression GenerateDivide(Expression left, Expression right)
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.DivideExpression(left, right);
                } 
 
                return Expression.Divide(left, right);
            } 

            /// Generates a modulo expression.
            /// Left expression.
            /// Right expression. 
            /// The generated expression.
            private static Expression GenerateModulo(Expression left, Expression right) 
            { 
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right))
                { 
                    return OpenTypeMethods.ModuloExpression(left, right);
                }

                return Expression.Modulo(left, right); 
            }
 
            /// Generates a logical And expression. 
            /// Left expression.
            /// Right expression. 
            /// The generated expression.
            private static Expression GenerateLogicalAnd(Expression left, Expression right)
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right)) 
                {
                    return OpenTypeMethods.AndAlsoExpression(left, right); 
                } 

                return Expression.AndAlso(left, right); 
            }

            /// Generates a Logical Or expression.
            /// Left expression. 
            /// Right expression.
            /// The generated expression. 
            private static Expression GenerateLogicalOr(Expression left, Expression right) 
            {
                if (IsOpenPropertyExpression(left) || IsOpenPropertyExpression(right)) 
                {
                    return OpenTypeMethods.OrElseExpression(left, right);
                }
 
                return Expression.OrElse(left, right);
            } 
 
            /// 
            /// Checks whether the specified  is part of an open property expression. 
            /// 
            /// Non-null  to check.
            /// true if  is based on an open property; false otherwise.
            private static bool IsOpenPropertyExpression(Expression expression) 
            {
                Debug.Assert(expression != null, "expression != null"); 
                return expression != WebUtil.NullLiteral && expression.Type == typeof(object) && IsOpenExpression(expression); 
            }
 
            /// Checks if the given input expression refers to open types.
            /// Input expression.
            /// true if the input is an open expression, false otherwise.
            private static bool IsOpenExpression(Expression input) 
            {
                Debug.Assert(input != null, "input != null"); 
                input = StripObjectConvert(input); 

                switch (input.NodeType) 
                {
                    case ExpressionType.Call:
                        return ((MethodCallExpression)input).Method.DeclaringType == typeof(OpenTypeMethods);
 
                    case ExpressionType.Negate:
                    case ExpressionType.Not: 
                        return ((UnaryExpression)input).Method != null && ((UnaryExpression)input).Method.DeclaringType == typeof(OpenTypeMethods); 

                    case ExpressionType.Add: 
                    case ExpressionType.AndAlso:
                    case ExpressionType.Divide:
                    case ExpressionType.Equal:
                    case ExpressionType.GreaterThan: 
                    case ExpressionType.GreaterThanOrEqual:
                    case ExpressionType.LessThan: 
                    case ExpressionType.LessThanOrEqual: 
                    case ExpressionType.Modulo:
                    case ExpressionType.Multiply: 
                    case ExpressionType.NotEqual:
                    case ExpressionType.OrElse:
                    case ExpressionType.Subtract:
                        return ((BinaryExpression)input).Method != null && ((BinaryExpression)input).Method.DeclaringType == typeof(OpenTypeMethods); 

                    case ExpressionType.Conditional: 
                        // This handles that null propagation scenario. 
                        return IsOpenExpression(((ConditionalExpression)input).IfFalse);
 
                    case ExpressionType.Convert:
                    case ExpressionType.Constant:
                    case ExpressionType.MemberAccess:
                    case ExpressionType.TypeIs: 
                        return false;
 
                    default: 
                        Debug.Assert(false, "Unexpected expression type found.");
                        break; 
                }

                return false;
            } 

            /// Strips all Expression.Convert(object) calls from the input expression. 
            /// Input expression. 
            /// First non-Convert expression inside Converts that converts to non-object type.
            private static Expression StripObjectConvert(Expression input) 
            {
                Debug.Assert(input != null, "input != null");
                while (input.NodeType == ExpressionType.Convert && input.Type == typeof(object))
                { 
                    UnaryExpression inner = (UnaryExpression)input;
                    input = inner.Operand; 
                } 

                return input; 
            }

            /// Gets a static method by name.
            /// Name of method to get. 
            /// Left expression to resolve method from and to use as argument.
            /// Right expression. 
            /// The method. 
            private static MethodInfo GetStaticMethod(string methodName, Expression left, Expression right)
            { 
                return left.Type.GetMethod(methodName, new Type[] { left.Type, right.Type });
            }

            /// Generates a static method call. 
            /// Method name.
            /// Left expression. 
            /// Right expression. 
            /// The generated expression.
            private static Expression GenerateStaticMethodCall(string methodName, Expression left, Expression right) 
            {
                return Expression.Call(null, GetStaticMethod(methodName, left, right), new Expression[] { left, right });
            }
 
            /// Creates an exception for a parse error.
            /// Message text. 
            /// A new Exception. 
            private static Exception ParseError(string message)
            { 
                return DataServiceException.CreateSyntaxError(message);
            }

            /// Checks that the given token has the specified identifier. 
            /// Token to check
            /// Identifier to check. 
            /// true if  is an identifier with the specified text. 
            private static bool TokenIdentifierIs(Token token, string id)
            { 
                return token.Id == TokenId.Identifier && String.Equals(id, token.Text, StringComparison.OrdinalIgnoreCase);
            }

            /// Creates an exception indicated that two operands are incompatible. 
            /// Name of operation for operands.
            /// Expression for left-hand operand. 
            /// Expression for right-hand operand. 
            /// Position for error.
            /// A new . 
            private static Exception IncompatibleOperandsError(string operationName, Expression left, Expression right, int pos)
            {
                string message = Strings.RequestQueryParser_IncompatibleOperands(
                    operationName, 
                    WebUtil.GetTypeName(left.Type),
                    WebUtil.GetTypeName(right.Type), 
                    pos); 
                return ParseError(message);
            } 

            #region Parsing.

            /// Handles 'null' literals. 
            /// Lexer to use for reading tokens
            /// The parsed expression. 
            private static Expression ParseNullLiteral(ExpressionLexer l) 
            {
                Debug.Assert(l.CurrentToken.Id == TokenId.NullLiteral, "l.CurrentToken.Id == TokenId.NullLiteral"); 
                l.NextToken();
                return WebUtil.NullLiteral;
            }
 
            /// Handles a ?: operator - not supported.
            /// The parsed expression. 
            private Expression ParseExpression() 
            {
                this.RecurseEnter(); 
                Expression expr = this.ParseLogicalOr();
                this.RecurseLeave();
                return expr;
            } 

            /// Handles or operator. 
            /// The parsed expression. 
            private Expression ParseLogicalOr()
            { 
                this.RecurseEnter();
                Expression left = this.ParseLogicalAnd();
                while (this.TokenIdentifierIs(ExpressionConstants.KeywordOr))
                { 
                    Token op = this.CurrentToken;
                    this.lexer.NextToken(); 
                    Expression right = this.ParseLogicalAnd(); 
                    this.CheckAndPromoteOperands(typeof(OperationSignatures.ILogicalSignatures), op.Text, ref left, ref right, op.Position);
                    left = GenerateLogicalOr(left, right); 
                }

                this.RecurseLeave();
                return left; 
            }
 
            /// Handles and operator. 
            /// The parsed expression.
            private Expression ParseLogicalAnd() 
            {
                this.RecurseEnter();
                Expression left = this.ParseComparison();
                while (this.TokenIdentifierIs(ExpressionConstants.KeywordAnd)) 
                {
                    Token op = this.CurrentToken; 
                    this.lexer.NextToken(); 
                    Expression right = this.ParseComparison();
                    this.CheckAndPromoteOperands(typeof(OperationSignatures.ILogicalSignatures), op.Text, ref left, ref right, op.Position); 
                    left = GenerateLogicalAnd(left, right);
                }

                this.RecurseLeave(); 
                return left;
            } 
 
            /// Handles eq, ne, lt, gt, le, ge operators.
            /// The parsed expression. 
            private Expression ParseComparison()
            {
                this.RecurseEnter();
                Expression left = this.ParseAdditive(); 
                while (this.CurrentToken.IsComparisonOperator)
                { 
                    Token op = this.CurrentToken; 
                    this.lexer.NextToken();
                    Expression right = this.ParseAdditive(); 
                    left = this.GenerateComparisonExpression(left, right, op);
                }

                this.RecurseLeave(); 
                return left;
            } 
 
            /// 
            /// Generates a comparison expression given a left hand side expression and literal for right hand side 
            /// 
            /// Left hand side experssions
            /// Literal for right hand side
            /// gt, eq or lt operator token 
            /// Resulting comparison expression
            private Expression GenerateComparison(Expression left, String rightLiteral, Token op) 
            { 
                ExpressionLexer l = new ExpressionLexer(rightLiteral);
                return this.GenerateComparisonExpression(left, this.ParsePrimaryStart(l), op); 
            }

            /// 
            /// Generates a comparison expression which can handle NULL values for any type. 
            /// NULL is always treated as the smallest possible value.
            /// So for example for strings NULL is smaller than any non-NULL string. 
            /// For now only GreaterThan and LessThan operators are supported by this method. 
            /// 
            /// Left hand side expression 
            /// Literal for the right hand side
            /// gt or lt operator token
            /// Resulting comparison expression (has a Boolean value)
            private Expression GenerateNullAwareComparison(Expression left, String rightLiteral, Token op) 
            {
                Debug.Assert( 
                    op.Text == ExpressionConstants.KeywordGreaterThan || op.Text == ExpressionConstants.KeywordLessThan, 
                    "Only GreaterThan or LessThan operators are supported by the GenerateNullAwateComparison method for now.");
 
                ExpressionLexer l = new ExpressionLexer(rightLiteral);
                Expression right = this.ParsePrimaryStart(l);

                if (WebUtil.TypeAllowsNull(left.Type)) 
                {
                    if (!WebUtil.TypeAllowsNull(right.Type)) 
                    { 
                        right = Expression.Convert(right, typeof(Nullable<>).MakeGenericType(right.Type));
                    } 
                }
                else if (WebUtil.TypeAllowsNull(right.Type))
                {
                    left = Expression.Convert(left, typeof(Nullable<>).MakeGenericType(left.Type)); 
                }
                else 
                { 
                    // Can't perform NULL aware comparison on this type. Just let the normal
                    // comparison deal with it. Since the type doesn't allow NULL one should 
                    // never appear, so normal comparison is just fine.
                    return this.GenerateComparisonExpression(left, right, op);
                }
 
                switch (op.Text)
                { 
                    case ExpressionConstants.KeywordGreaterThan: 
                        // (left != null) && ((right == null) || Compare(left, right) > 0)
                        if (left == WebUtil.NullLiteral) 
                        {
                            return Expression.Constant(false, typeof(bool));
                        }
                        else if (right == WebUtil.NullLiteral) 
                        {
                            return GenerateNotEqual(left, Expression.Constant(null, left.Type)); 
                        } 
                        else
                        { 
                            return GenerateLogicalAnd(
                                        GenerateNotEqual(left, Expression.Constant(null, left.Type)),
                                        GenerateLogicalOr(
                                            GenerateEqual(right, Expression.Constant(null, right.Type)), 
                                            this.GenerateComparisonExpression(left, right, op)));
                        } 
 
                    case ExpressionConstants.KeywordLessThan:
                        // (right != null) && ((left == null) || Compare(left, right) < 0) 
                        if (right == WebUtil.NullLiteral)
                        {
                            return Expression.Constant(false, typeof(bool));
                        } 
                        else if (left == WebUtil.NullLiteral)
                        { 
                            return GenerateNotEqual(right, Expression.Constant(null, right.Type)); 
                        }
                        else 
                        {
                            return GenerateLogicalAnd(
                                        GenerateNotEqual(right, Expression.Constant(null, left.Type)),
                                        GenerateLogicalOr( 
                                            GenerateEqual(left, Expression.Constant(null, right.Type)),
                                            this.GenerateComparisonExpression(left, right, op))); 
                        } 

                    default: 
                        // For now only < and > are supported as we use this only from $skiptoken
                        throw ParseError(
                            Strings.RequestQueryParser_NullOperatorUnsupported(op.Text, op.Position, this.lexer.ExpressionText));
                } 
            }
 
            ///  
            /// Given left and right hand side expressions, generates a comparison expression based
            /// on the given comparison token 
            /// 
            /// Left hand side expression
            /// Right hand side expression
            /// Comparison operator 
            /// Resulting comparison expression
            private Expression GenerateComparisonExpression(Expression left, Expression right, Token op) 
            { 
                bool equality = op.IsEqualityOperator;
                if (equality && !left.Type.IsValueType && !right.Type.IsValueType) 
                {
                    if (left.Type != right.Type)
                    {
                        if (WebUtil.IsNullConstant(left)) 
                        {
                            left = Expression.Constant(null, right.Type); 
                        } 
                        else if (WebUtil.IsNullConstant(right))
                        { 
                            right = Expression.Constant(null, left.Type);
                        }
                        else if (left.Type.IsAssignableFrom(right.Type))
                        { 
                            right = Expression.Convert(right, left.Type);
                        } 
                        else if (right.Type.IsAssignableFrom(left.Type)) 
                        {
                            left = Expression.Convert(left, right.Type); 
                        }
                        else
                        {
                            throw ExpressionParser.IncompatibleOperandsError(op.Text, left, right, op.Position); 
                        }
                    } 
                } 
                else if (left == WebUtil.NullLiteral || right == WebUtil.NullLiteral)
                { 
                    if (!equality)
                    {
                        throw ParseError(
                            Strings.RequestQueryParser_NullOperatorUnsupported(op.Text, op.Position, this.lexer.ExpressionText)); 
                    }
 
                    // Because we don't have an explicit "is null" check, literal comparisons 
                    // to null are special.
                    if (!WebUtil.TypeAllowsNull(left.Type)) 
                    {
                        left = Expression.Convert(left, typeof(Nullable<>).MakeGenericType(left.Type));
                    }
                    else if (!WebUtil.TypeAllowsNull(right.Type)) 
                    {
                        right = Expression.Convert(right, typeof(Nullable<>).MakeGenericType(right.Type)); 
                    } 
                }
                else 
                {
                    // Enums should be checked here for promotion when supported, but they aren't in this version.
                    Debug.Assert(!IsEnumType(left.Type), "!IsEnumType(left.Type)");
                    Debug.Assert(!IsEnumType(right.Type), "!IsEnumType(right.Type)"); 

                    Type signatures = equality ? typeof(OperationSignatures.IEqualitySignatures) : typeof(OperationSignatures.IRelationalSignatures); 
                    this.CheckAndPromoteOperands(signatures, op.Text, ref left, ref right, op.Position); 
                }
 
                Debug.Assert(op.Id == TokenId.Identifier, "op.id == TokenId.Identifier");
                MethodInfo comparisonMethodInfo = null;
                if (!equality)
                { 
                    if (left.Type == typeof(string))
                    { 
                        comparisonMethodInfo = StringCompareMethodInfo; 
                    }
                    else 
                    if (left.Type == typeof(bool))
                    {
                        comparisonMethodInfo = BoolCompareMethodInfo;
                    } 
                    else if (left.Type == typeof(bool?))
                    { 
                        comparisonMethodInfo = BoolCompareMethodInfoNullable; 
                    }
                    else 
                    if (left.Type == typeof(Guid))
                    {
                        comparisonMethodInfo = GuidCompareMethodInfo;
                    } 
                    else
                    if (left.Type == typeof(Guid?)) 
                    { 
                        comparisonMethodInfo = GuidCompareMethodInfoNullable;
                    } 
                }

                switch (op.Text)
                { 
                    case ExpressionConstants.KeywordEqual:
                        left = GenerateEqual(left, right); 
                        break; 
                    case ExpressionConstants.KeywordNotEqual:
                        left = GenerateNotEqual(left, right); 
                        break;
                    case ExpressionConstants.KeywordGreaterThan:
                        left = GenerateGreaterThan(left, right, comparisonMethodInfo);
                        break; 
                    case ExpressionConstants.KeywordGreaterThanOrEqual:
                        left = GenerateGreaterThanEqual(left, right, comparisonMethodInfo); 
                        break; 
                    case ExpressionConstants.KeywordLessThan:
                        left = GenerateLessThan(left, right, comparisonMethodInfo); 
                        break;
                    case ExpressionConstants.KeywordLessThanOrEqual:
                        left = GenerateLessThanEqual(left, right, comparisonMethodInfo);
                        break; 
                }
 
                return left; 
            }
 
            /// Handles +, -, & operators (& for string concat, not supported).
            /// The parsed expression.
            private Expression ParseAdditive()
            { 
                this.RecurseEnter();
                Expression left = this.ParseMultiplicative(); 
                while (this.CurrentToken.IdentifierIs(ExpressionConstants.KeywordAdd) || 
                    this.CurrentToken.IdentifierIs(ExpressionConstants.KeywordSub))
                { 
                    Token op = this.CurrentToken;
                    this.lexer.NextToken();
                    Expression right = this.ParseMultiplicative();
                    if (op.IdentifierIs(ExpressionConstants.KeywordAdd)) 
                    {
                        this.CheckAndPromoteOperands(typeof(OperationSignatures.IAddSignatures), op.Text, ref left, ref right, op.Position); 
                        left = GenerateAdd(left, right); 
                    }
                    else 
                    {
                        Debug.Assert(ExpressionParser.TokenIdentifierIs(op, ExpressionConstants.KeywordSub), "ExpressionParser.TokenIdentifierIs(op, ExpressionConstants.KeywordSub)");
                        this.CheckAndPromoteOperands(typeof(OperationSignatures.ISubtractSignatures), op.Text, ref left, ref right, op.Position);
                        left = GenerateSubtract(left, right); 
                    }
                } 
 
                this.RecurseLeave();
                return left; 
            }

            /// Handles mul, div, mod operators.
            /// The parsed expression. 
            private Expression ParseMultiplicative()
            { 
                this.RecurseEnter(); 
                Expression left = this.ParseUnary();
                while (this.CurrentToken.IdentifierIs(ExpressionConstants.KeywordMultiply) || 
                    this.CurrentToken.IdentifierIs(ExpressionConstants.KeywordDivide) ||
                    this.CurrentToken.IdentifierIs(ExpressionConstants.KeywordModulo))
                {
                    Token op = this.CurrentToken; 
                    this.lexer.NextToken();
                    Expression right = this.ParseUnary(); 
                    this.CheckAndPromoteOperands(typeof(OperationSignatures.IArithmeticSignatures), op.Text, ref left, ref right, op.Position); 
                    if (op.IdentifierIs(ExpressionConstants.KeywordMultiply))
                    { 
                        left = GenerateMultiply(left, right);
                    }
                    else if (op.IdentifierIs(ExpressionConstants.KeywordDivide))
                    { 
                        left = GenerateDivide(left, right);
                    } 
                    else 
                    {
                        Debug.Assert(op.IdentifierIs(ExpressionConstants.KeywordModulo), "op.IdentifierIs(ExpressionConstants.KeywordModulo)"); 
                        left = GenerateModulo(left, right);
                    }
                }
 
                this.RecurseLeave();
                return left; 
            } 

            /// Handles -, not unary operators. 
            /// The parsed expression.
            private Expression ParseUnary()
            {
                this.RecurseEnter(); 
                if (this.CurrentToken.Id == TokenId.Minus || this.CurrentToken.IdentifierIs(ExpressionConstants.KeywordNot))
                { 
                    Token op = this.CurrentToken; 
                    this.lexer.NextToken();
                    if (op.Id == TokenId.Minus && (ExpressionLexer.IsNumeric(this.CurrentToken.Id))) 
                    {
                        Token numberLiteral = this.CurrentToken;
                        numberLiteral.Text = "-" + numberLiteral.Text;
                        numberLiteral.Position = op.Position; 
                        this.CurrentToken = numberLiteral;
                        this.RecurseLeave(); 
                        return this.ParsePrimary(); 
                    }
 
                    Expression expr = this.ParseUnary();
                    if (op.Id == TokenId.Minus)
                    {
                        this.CheckAndPromoteOperand(typeof(OperationSignatures.INegationSignatures), op.Text, ref expr, op.Position); 
                        expr = GenerateNegate(expr);
                    } 
                    else 
                    {
                        this.CheckAndPromoteOperand(typeof(OperationSignatures.INotSignatures), op.Text, ref expr, op.Position); 
                        expr = GenerateNot(expr);
                    }

                    this.RecurseLeave(); 
                    return expr;
                } 
 
                this.RecurseLeave();
                return this.ParsePrimary(); 
            }

            /// Handles primary expressions.
            /// The parsed expression. 
            private Expression ParsePrimary()
            { 
                this.RecurseEnter(); 
                Expression expr = this.ParsePrimaryStart(this.lexer);
                while (true) 
                {
                    if (this.CurrentToken.Id == TokenId.Slash)
                    {
                        this.lexer.NextToken(); 
                        expr = this.ParseMemberAccess(expr);
                    } 
                    else 
                    {
                        break; 
                    }
                }

                this.RecurseLeave(); 
                return expr;
            } 
 
            /// Handles the start of primary expressions.
            /// Lexer to use for reading tokens 
            /// The parsed expression.
            private Expression ParsePrimaryStart(ExpressionLexer l)
            {
                switch (l.CurrentToken.Id) 
                {
                    case TokenId.BooleanLiteral: 
                        return this.ParseTypedLiteral(typeof(bool), XmlConstants.EdmBooleanTypeName, l); 
                    case TokenId.DateTimeLiteral:
                        return this.ParseTypedLiteral(typeof(DateTime), XmlConstants.EdmDateTimeTypeName, l); 
                    case TokenId.DecimalLiteral:
                        return this.ParseTypedLiteral(typeof(decimal), XmlConstants.EdmDecimalTypeName, l);
                    case TokenId.NullLiteral:
                        return ExpressionParser.ParseNullLiteral(l); 
                    case TokenId.Identifier:
                        Debug.Assert(Object.ReferenceEquals(this.lexer, l), "Lexer should be the member lexer"); 
                        return this.ParseIdentifier(); 
                    case TokenId.StringLiteral:
                        return this.ParseTypedLiteral(typeof(string), XmlConstants.EdmStringTypeName, l); 
                    case TokenId.Int64Literal:
                        return this.ParseTypedLiteral(typeof(Int64), XmlConstants.EdmInt64TypeName, l);
                    case TokenId.IntegerLiteral:
                        return this.ParseTypedLiteral(typeof(Int32), XmlConstants.EdmInt32TypeName, l); 
                    case TokenId.DoubleLiteral:
                        return this.ParseTypedLiteral(typeof(double), XmlConstants.EdmDoubleTypeName, l); 
                    case TokenId.SingleLiteral: 
                        return this.ParseTypedLiteral(typeof(Single), XmlConstants.EdmSingleTypeName, l);
                    case TokenId.GuidLiteral: 
                        return this.ParseTypedLiteral(typeof(Guid), XmlConstants.EdmGuidTypeName, l);
                    case TokenId.BinaryLiteral:
                        return this.ParseTypedLiteral(typeof(byte[]), XmlConstants.EdmBinaryTypeName, l);
                    case TokenId.OpenParen: 
                        Debug.Assert(Object.ReferenceEquals(this.lexer, l), "Lexer should be the member lexer");
                        return this.ParseParenExpression(); 
                    default: 
                        throw ParseError(Strings.RequestQueryParser_ExpressionExpected(l.CurrentToken.Position));
                } 
            }

            /// Handles parenthesized expressions.
            /// The parsed expression. 
            private Expression ParseParenExpression()
            { 
                if (this.CurrentToken.Id != TokenId.OpenParen) 
                {
                    throw ParseError(Strings.RequestQueryParser_OpenParenExpected(this.CurrentToken.Position)); 
                }

                this.lexer.NextToken();
                Expression e = this.ParseExpression(); 
                if (this.CurrentToken.Id != TokenId.CloseParen)
                { 
                    throw ParseError(Strings.RequestQueryParser_CloseParenOrOperatorExpected(this.CurrentToken.Position)); 
                }
 
                this.lexer.NextToken();
                return e;
            }
 
            /// Handles identifiers.
            /// The parsed expression. 
            private Expression ParseIdentifier() 
            {
                this.ValidateToken(TokenId.Identifier); 

                // An open paren here would indicate calling a method in regular C# syntax.
                bool identifierIsFunction = this.lexer.PeekNextToken().Id == TokenId.OpenParen;
                if (identifierIsFunction) 
                {
                    return this.ParseIdentifierAsFunction(); 
                } 
                else
                { 
                    this.currentSegmentInfo = new SegmentTypeInfo(this.typeForIt, this.setForIt, false);
                    return this.ParseMemberAccess(this.it);
                }
            } 

            /// Handles identifiers which have been recognized as functions. 
            /// The parsed expression. 
            private Expression ParseIdentifierAsFunction()
            { 
                FunctionDescription[] functionDescriptions;
                Token functionToken = this.CurrentToken;
                if (!functions.TryGetValue(functionToken.Text, out functionDescriptions))
                { 
                    throw ParseError(Strings.RequestQueryParser_UnknownFunction(functionToken.Text, functionToken.Position));
                } 
 
                this.lexer.NextToken();
                Expression[] originalArguments = this.ParseArgumentList(); 
                Expression[] arguments = this.nullPropagationRequired ? originalArguments : (Expression[])originalArguments.Clone();
                Expression candidateTypeArgument = arguments.Length > 1 ? arguments[1] :
                                                   arguments.Length > 0 ? arguments[0] :
                                                   null; 

                // check if the one of the parameters is of open type. If yes, then we need to invoke 
                // LateBoundMethods for this function otherwise not. 
                bool openParameters = false;
                if (!functionDescriptions[0].IsTypeCast && !functionDescriptions[0].IsTypeCheck) 
                {
                    foreach (Expression argument in arguments)
                    {
                        if (IsOpenPropertyExpression(argument)) 
                        {
                            openParameters = true; 
                            break; 
                        }
                    } 
                }

                Expression result = null;
                FunctionDescription function = null; 
                if (openParameters)
                { 
                    foreach (FunctionDescription functionDescription in functionDescriptions) 
                    {
                        if (functionDescription.ParameterTypes.Length == arguments.Length) 
                        {
                            function = functionDescription;
                            break;
                        } 
                    }
 
                    Expression[] openArguments = new Expression[arguments.Length]; 
                    for (int i = 0; i < openArguments.Length; i++)
                    { 
                        if (IsOpenPropertyExpression(arguments[i]))
                        {
                            openArguments[i] = arguments[i];
                        } 
                        else
                        { 
                            openArguments[i] = Expression.Convert(arguments[i], typeof(object)); 
                        }
                    } 

                    if (function == null)
                    {
                        string message = Strings.RequestQueryParser_NoApplicableFunction( 
                            functionToken.Text,
                            functionToken.Position, 
                            FunctionDescription.BuildSignatureList(functionToken.Text, functionDescriptions)); 
                        throw ParseError(message);
                    } 

                    result = function.InvokeOpenTypeMethod(openArguments);
                }
                else 
                {
                    function = this.FindBestFunction(functionDescriptions, ref arguments); 
                    if (function == null) 
                    {
                        string message = Strings.RequestQueryParser_NoApplicableFunction( 
                            functionToken.Text,
                            functionToken.Position,
                            FunctionDescription.BuildSignatureList(functionToken.Text, functionDescriptions));
                        throw ParseError(message); 
                    }
 
                    // Special case for null propagation - we never strip nullability from expressions. 
                    if (this.nullPropagationRequired && function.IsTypeCast)
                    { 
                        Expression typeExpression = arguments[arguments.Length - 1];
                        Debug.Assert(typeExpression != null, "typeExpression != null -- otherwise function finding failed.");
                        if (typeExpression.Type == typeof(Type))
                        { 
                            Type castTargetType = (Type)((ConstantExpression)typeExpression).Value;
                            if (!WebUtil.TypeAllowsNull(castTargetType)) 
                            { 
                                arguments[arguments.Length - 1] = Expression.Constant(typeof(Nullable<>).MakeGenericType(castTargetType));
                            } 
                        }
                    }

                    Expression[] finalArguments; 
                    if (function.ConversionFunction == FunctionDescription.BinaryIsOfResourceType ||
                        function.ConversionFunction == FunctionDescription.BinaryCastResourceType) 
                    { 
                        finalArguments = new Expression[arguments.Length + 1];
                        for (int i = 0; i < arguments.Length; i++) 
                        {
                            finalArguments[i] = arguments[i];
                        }
 
                        finalArguments[arguments.Length] = Expression.Constant(IsOpenPropertyExpression(arguments[0]), typeof(bool));
                    } 
                    else 
                    {
                        finalArguments = arguments; 
                    }

                    result = function.ConversionFunction(this.it, finalArguments);
                } 

                if (this.nullPropagationRequired && !function.IsTypeCheck && !function.IsTypeCast) 
                { 
                    Debug.Assert(
                        originalArguments.Length == arguments.Length, 
                        "originalArguments.Length == arguments.Length -- arguments should not be added/removed");
                    for (int i = 0; i < originalArguments.Length; i++)
                    {
                        result = this.ConsiderNullPropagation(originalArguments[i], result); 
                    }
                } 
 
                // type casts change the type of the "current" item, reflect this in parser state
                if (function.IsTypeCast) 
                {
                    Debug.Assert(candidateTypeArgument != null, "Should have failed to bind to the function if arguments don't match");
                    Debug.Assert(candidateTypeArgument.Type == typeof(string), "First argument to 'cast' should have been a string");
                    Debug.Assert(candidateTypeArgument.NodeType == ExpressionType.Constant, "Non-constant in type name for a cast?"); 

                    this.currentSegmentInfo = new SegmentTypeInfo( 
                        WebUtil.TryResolveResourceType(this.provider, (string)((ConstantExpression)candidateTypeArgument).Value), 
                        this.currentSegmentInfo != null ? this.currentSegmentInfo.ResourceSet : this.setForIt,
                        this.currentSegmentInfo != null ? this.currentSegmentInfo.IsCollection : false); 
                }

                return result;
            } 

            /// Handles boolean literals. 
            /// The parsed expression. 
            private Expression ParseBooleanLiteral()
            { 
                Debug.Assert(this.CurrentToken.Id == TokenId.BooleanLiteral, "this.CurrentToken.Id == TokenId.BooleanLiteral");
                string originalText = this.CurrentToken.Text;
                this.lexer.NextToken();
                if (originalText == ExpressionConstants.KeywordTrue) 
                {
                    return trueLiteral; 
                } 
                else
                { 
                    Debug.Assert(originalText == ExpressionConstants.KeywordFalse, "originalText == ExpressionConstants.KeywordFalse");
                    return falseLiteral;
                }
            } 

            /// Handles typed literals. 
            /// Expected type to be parsed. 
            /// Expected type name.
            /// Lexer to use for reading tokens 
            /// The constants expression produced by building the given literal.
            private Expression ParseTypedLiteral(Type targetType, string targetTypeName, ExpressionLexer l)
            {
                object targetValue; 
                if (!WebConvert.TryKeyStringToPrimitive(l.CurrentToken.Text, targetType, out targetValue))
                { 
                    string message = Strings.RequestQueryParser_UnrecognizedLiteral(targetTypeName, l.CurrentToken.Text, l.CurrentToken.Position); 
                    throw ParseError(message);
                } 

                Expression result = this.CreateLiteral(targetValue, l.CurrentToken.Text);
                l.NextToken();
                return result; 
            }
 
            /// Handles member access. 
            /// Instance being accessed.
            /// The parsed expression. 
            private Expression ParseMemberAccess(Expression instance)
            {
                Debug.Assert(instance != null, "instance != null");
 
                Type type = instance.Type;
                int errorPos = this.lexer.Position; 
                string id = this.CurrentToken.GetIdentifier(); 
                this.lexer.NextToken();
 
                // Disallow the member access for a collection property.
                Debug.Assert(this.currentSegmentInfo != null, "Must have initialized current segment information.");
                if (this.currentSegmentInfo.IsCollection)
                { 
                    throw ParseError(Strings.RequestQueryParser_UnknownProperty(id, WebUtil.GetTypeName(type), errorPos));
                } 
 
                // An open paren here would indicate calling a method in regular C# syntax.
                ResourceProperty property = this.currentSegmentInfo.ResourceType == null ? 
                                                null : // null means the current segment was already an open type
                                                this.currentSegmentInfo.ResourceType.TryResolvePropertyName(id);

                ResourceSetWrapper container = this.currentSegmentInfo.ResourceSet == null || property == null || property.TypeKind != ResourceTypeKind.EntityType ? 
                                    null :
                                    this.provider.GetContainer(this.currentSegmentInfo.ResourceSet, this.currentSegmentInfo.ResourceType, property); 
 
                if (property != null)
                { 
                    if (property.TypeKind == ResourceTypeKind.EntityType && container == null)
                    {
                        throw DataServiceException.CreateBadRequestError(Strings.BadRequest_InvalidPropertyNameSpecified(id, this.currentSegmentInfo.ResourceType.FullName));
                    } 

                    // We have a strongly-type property. 
                    Expression propertyAccess; 
                    if (property.CanReflectOnInstanceTypeProperty)
                    { 
                        propertyAccess = Expression.Property(instance, this.currentSegmentInfo.ResourceType.GetPropertyInfo(property));
                    }
                    else
                    { 
                        // object DataServiceProviderMethods.GetValue(object, ResourceProperty)
                        propertyAccess = Expression.Call( 
                                            null, /*instance*/ 
                                            DataServiceProviderMethods.GetValueMethodInfo,
                                            instance, 
                                            Expression.Constant(property));
                        propertyAccess = Expression.Convert(propertyAccess, property.Type);
                    }
 
                    Expression result = this.ConsiderNullPropagation(instance, propertyAccess);
                    if (container != null) 
                    { 
                        bool singleResult = property.Kind == ResourcePropertyKind.ResourceReference;
                        DataServiceConfiguration.CheckResourceRightsForRead(container, singleResult); 
                        Expression filter = DataServiceConfiguration.ComposeQueryInterceptors(this.service, container);
                        if (filter != null)
                        {
                            // We did null propagation for accessing the property, but we may also need 
                            // to do null propagation on the property value itself (otherwise the interception
                            // lambda needs to check the argument for null, which is probably unexpected). 
                            result = RequestQueryProcessor.ComposePropertyNavigation( 
                                result, (LambdaExpression)filter, this.provider.NullPropagationRequired);
                        } 
                    }

                    this.currentSegmentInfo = new SegmentTypeInfo(
                                    property.ResourceType, 
                                    container,
                                    property.Kind == ResourcePropertyKind.ResourceSetReference); 
                    return result; 
                }
                else 
                {
                    ResourceType resourceType = this.currentSegmentInfo.ResourceType;
                    this.currentSegmentInfo = new SegmentTypeInfo(null, null, false);
 
                    // Open types can have any members inside them
                    if (resourceType == null || resourceType.IsOpenType) 
                    { 
                        // object OpenTypeMethods.GetValue(object, string)
                        Expression call = 
                            Expression.Call(null /* instance */, OpenTypeMethods.GetValueOpenPropertyMethodInfo, instance, Expression.Constant(id));
                        return this.ConsiderNullPropagation(instance, call);
                    }
                    else 
                    {
                        throw ParseError(Strings.RequestQueryParser_UnknownProperty(id, WebUtil.GetTypeName(type), errorPos)); 
                    } 
                }
            } 

            /// Handles argument lists.
            /// The parsed expressions.
            private Expression[] ParseArgumentList() 
            {
                if (this.CurrentToken.Id != TokenId.OpenParen) 
                { 
                    throw ParseError(Strings.RequestQueryParser_OpenParenExpected(this.CurrentToken.Position));
                } 

                this.lexer.NextToken();
                Expression[] args = this.CurrentToken.Id != TokenId.CloseParen ? this.ParseArguments() : emptyExpressions;
                if (this.CurrentToken.Id != TokenId.CloseParen) 
                {
                    throw ParseError(Strings.RequestQueryParser_CloseParenOrCommaExpected(this.CurrentToken.Position)); 
                } 

                this.lexer.NextToken(); 
                return args;
            }

            /// Handles comma-separated arguments. 
            /// The parsed expressions.
            private Expression[] ParseArguments() 
            { 
                List argList = new List();
                while (true) 
                {
                    argList.Add(this.ParseExpression());
                    if (this.CurrentToken.Id != TokenId.Comma)
                    { 
                        break;
                    } 
 
                    this.lexer.NextToken();
                } 

                return argList.ToArray();
            }
 
            #endregion Parsing.
 
            /// Creates a constant expression with the specified literal. 
            /// Constant value.
            /// Value text. 
            /// The created expression.
            private Expression CreateLiteral(object value, string text)
            {
                // DEVNOTE([....]): 
                // The following code rely on Expression.Constant returning UNIQUE instances for every call to it
                // i.e., Expression.Constant(1) does not reference equals to Expression.Constant(1) 
                ConstantExpression expr = Expression.Constant(value); 
                this.literals.Add(expr, text);
                return expr; 
            }

            /// Finds the best fitting function for the specified arguments.
            /// Functions to consider. 
            /// Arguments; if a best function is found, promoted arguments.
            /// The best fitting function; null if none found or ambiguous. 
            private FunctionDescription FindBestFunction(FunctionDescription[] functions, ref Expression[] arguments) 
            {
                Debug.Assert(functions != null, "functions != null"); 
                List applicableFunctions = new List(functions.Length);
                List applicablePromotedArguments = new List(functions.Length);

                // Build a list of applicable functions (and cache their promoted arguments). 
                foreach (FunctionDescription candidate in functions)
                { 
                    if (candidate.ParameterTypes.Length != arguments.Length) 
                    {
                        continue; 
                    }

                    Expression[] promotedArguments = new Expression[arguments.Length];
                    bool argumentsMatch = true; 
                    for (int i = 0; i < candidate.ParameterTypes.Length; i++)
                    { 
                        promotedArguments[i] = this.PromoteExpression(arguments[i], candidate.ParameterTypes[i], true); 
                        if (promotedArguments[i] == null)
                        { 
                            argumentsMatch = false;
                            break;
                        }
                    } 

                    if (argumentsMatch) 
                    { 
                        applicableFunctions.Add(candidate);
                        applicablePromotedArguments.Add(promotedArguments); 
                    }
                }

                // Return the best applicable function. 
                if (applicableFunctions.Count == 0)
                { 
                    // No matching function. 
                    return null;
                } 
                else if (applicableFunctions.Count == 1)
                {
                    arguments = applicablePromotedArguments[0];
                    return applicableFunctions[0]; 
                }
                else 
                { 
                    // Find a single function which is better than all others.
                    int bestFunctionIndex = -1; 
                    for (int i = 0; i < applicableFunctions.Count; i++)
                    {
                        bool betterThanAllOthers = true;
                        for (int j = 0; j < applicableFunctions.Count; j++) 
                        {
                            if (i != j && IsBetterThan(arguments, applicableFunctions[j].ParameterTypes, applicableFunctions[i].ParameterTypes)) 
                            { 
                                betterThanAllOthers = false;
                                break; 
                            }
                        }

                        if (betterThanAllOthers) 
                        {
                            if (bestFunctionIndex == -1) 
                            { 
                                bestFunctionIndex = i;
                            } 
                            else
                            {
                                // Ambiguous.
                                return null; 
                            }
                        } 
                    } 

                    if (bestFunctionIndex == -1) 
                    {
                        return null;
                    }
 
                    arguments = applicablePromotedArguments[bestFunctionIndex];
                    return applicableFunctions[bestFunctionIndex]; 
                } 
            }
 
            /// Rewrites an expression to propagate null values if necessary.
            /// Expression to check for null.
            /// Expression to yield if  does not yield null.
            /// The possibly rewriteen . 
            private Expression ConsiderNullPropagation(Expression element, Expression notNullExpression)
            { 
                if (!this.nullPropagationRequired || element == this.it || !WebUtil.TypeAllowsNull(element.Type)) 
                {
                    return notNullExpression; 
                }

                // Tiny optimization: remove the check on constants which are known not to be null.
                // Otherwise every string literal propagates out, which is correct but unnecessarily messy. 
                if (element is ConstantExpression && element != WebUtil.NullLiteral)
                { 
                    return notNullExpression; 
                }
 
                // ifTrue and ifFalse expressions must match exactly. We need to ensure that the 'false'
                // side is nullable, and the 'true' side is a null of the correct type.
                Expression test = Expression.Equal(element, Expression.Constant(null, element.Type));
                Expression falseIf = notNullExpression; 
                if (!WebUtil.TypeAllowsNull(falseIf.Type))
                { 
                    falseIf = Expression.Convert(falseIf, typeof(Nullable<>).MakeGenericType(falseIf.Type)); 
                }
 
                Expression trueIf = Expression.Constant(null, falseIf.Type);
                return Expression.Condition(test, trueIf, falseIf);
            }
 
            /// Checks that the operand (possibly promoted) is valid for the specified operation.
            /// Type with signatures to match. 
            /// Name of operation for error reporting. 
            /// Expression for operand.
            /// Position for error reporting. 
            private void CheckAndPromoteOperand(Type signatures, string operationName, ref Expression expr, int errorPos)
            {
                Debug.Assert(signatures != null, "signatures != null");
                Debug.Assert(operationName != null, "operationName != null"); 
                Expression[] args = new Expression[] { expr };
                MethodBase method; 
                if (this.FindMethod(signatures, "F", args, out method) != 1) 
                {
                    throw ParseError(Strings.RequestQueryParser_IncompatibleOperand(operationName, WebUtil.GetTypeName(args[0].Type), errorPos)); 
                }

                expr = args[0];
            } 

            /// Checks that the operands (possibly promoted) are valid for the specified operation. 
            /// Type with signatures to match. 
            /// Name of operation for error reporting.
            /// Expression for left operand. 
            /// Expression for right operand.
            /// Position for error reporting.
            private void CheckAndPromoteOperands(Type signatures, string operationName, ref Expression left, ref Expression right, int errorPos)
            { 
                Expression[] args = new Expression[] { left, right };
                MethodBase method; 
                if (this.FindMethod(signatures, "F", args, out method) != 1) 
                {
                    throw ExpressionParser.IncompatibleOperandsError(operationName, left, right, errorPos); 
                }

                left = args[0];
                right = args[1]; 
            }
 
            /// Finds the named method in the specifid type. 
            /// Type to look in.
            /// Name of method to look for. 
            /// Arguments to method.
            /// Best method found.
            /// Number of matching methods.
            private int FindMethod(Type type, string methodName, Expression[] args, out MethodBase method) 
            {
                BindingFlags flags = BindingFlags.Public | BindingFlags.DeclaredOnly | BindingFlags.Static | BindingFlags.Instance; 
                foreach (Type t in SelfAndBaseTypes(type)) 
                {
                    MemberInfo[] members = t.FindMembers(MemberTypes.Method, flags, Type.FilterName, methodName); 
                    int count = this.FindBestMethod(members.Cast(), args, out method);
                    if (count != 0)
                    {
                        return count; 
                    }
                } 
 
                method = null;
                return 0; 
            }

            /// Finds all applicable methods from the specified enumeration that match the arguments.
            /// Enumerable object of candidate methods. 
            /// Argument expressions.
            /// Methods that apply to the specified arguments. 
            private MethodData[] FindApplicableMethods(IEnumerable methods, Expression[] args) 
            {
                List result = new List(); 
                foreach (MethodBase method in methods)
                {
                    MethodData methodData = new MethodData(method, method.GetParameters());
                    if (this.IsApplicable(methodData, args)) 
                    {
                        result.Add(methodData); 
                    } 
                }
 
                return result.ToArray();
            }

            /// Finds the best methods for the specified arguments given a candidate method enumeration. 
            /// Enumerable object for candidate methods.
            /// Argument expressions to match. 
            /// Best matched method. 
            /// The number of "best match" methods.
            private int FindBestMethod(IEnumerable methods, Expression[] args, out MethodBase method) 
            {
                MethodData[] applicable = this.FindApplicableMethods(methods, args);
                if (applicable.Length > 1)
                { 
                    applicable = FindBestApplicableMethods(applicable, args);
                } 
 
                int result = applicable.Length;
                method = null; 
                if (applicable.Length == 1)
                {
                    // If we started off with all non-OpenType expressions and end with all-OpenType
                    // expressions, we've been too aggresive - the transition from non-open-types 
                    // to open types should initially happen only as a result of accessing open properties.
                    MethodData md = applicable[0]; 
                    bool originalArgsDefined = true; 
                    bool promotedArgsOpen = true;
                    for (int i = 0; i < args.Length; i++) 
                    {
                        originalArgsDefined = originalArgsDefined && !IsOpenPropertyExpression(args[i]);
                        promotedArgsOpen = promotedArgsOpen && md.Parameters[i].ParameterType == typeof(object);
                        args[i] = md.Args[i]; 
                    }
 
                    method = (originalArgsDefined && promotedArgsOpen) ? null : md.MethodBase; 
                    result = (method == null) ? 0 : 1;
                } 
                else if (applicable.Length > 1)
                {
                    // We may have the case for operators (which C# doesn't) in which we have a nullable operand
                    // and a non-nullable operand. We choose to convert the one non-null operand to nullable in that 
                    // case (the binary expression will lift to null).
                    if (args.Length == 2 && applicable.Length == 2 && 
                        GetNonNullableType(applicable[0].Parameters[0].ParameterType) == 
                        GetNonNullableType(applicable[1].Parameters[0].ParameterType))
                    { 
                        MethodData nullableMethod =
                            WebUtil.TypeAllowsNull(applicable[0].Parameters[0].ParameterType) ?
                            applicable[0] :
                            applicable[1]; 
                        args[0] = nullableMethod.Args[0];
                        args[1] = nullableMethod.Args[1]; 
                        return this.FindBestMethod(methods, args, out method); 
                    }
                } 

                return result;
            }
 
            /// Checks whether the specified method is applicable given the argument expressions.
            /// Method to check. 
            /// Argument expressions. 
            /// true if the method is applicable; false otherwise.
            private bool IsApplicable(MethodData method, Expression[] args) 
            {
                if (method.Parameters.Length != args.Length)
                {
                    return false; 
                }
 
                Expression[] promotedArgs = new Expression[args.Length]; 
                for (int i = 0; i < args.Length; i++)
                { 
                    ParameterInfo pi = method.Parameters[i];
                    Debug.Assert(!pi.IsOut, "!pi.IsOut");
                    Expression promoted = this.PromoteExpression(args[i], pi.ParameterType, false);
                    if (promoted == null) 
                    {
                        return false; 
                    } 

                    promotedArgs[i] = promoted; 
                }

                method.Args = promotedArgs;
                return true; 
            }
 
            /// Promotes the specified expression to the given type if necessary. 
            /// Expression to promote.
            /// Type to change expression to. 
            /// Whether an exact type is required; false implies a compatible type is OK.
            /// Expression with the promoted type.
            private Expression PromoteExpression(Expression expr, Type type, bool exact)
            { 
                Debug.Assert(expr != null, "expr != null");
                Debug.Assert(type != null, "type != null"); 
                if (expr.Type == type) 
                {
                    return expr; 
                }

                ConstantExpression ce = expr as ConstantExpression;
                if (ce != null) 
                {
                    if (ce == WebUtil.NullLiteral) 
                    { 
                        if (WebUtil.TypeAllowsNull(type))
                        { 
                            return Expression.Constant(null, type);
                        }
                    }
                    else 
                    {
                        string text; 
                        if (this.literals.TryGetValue(ce, out text)) 
                        {
                            Type target = GetNonNullableType(type); 
                            object value = null;
                            if (ce.Type == typeof(string) && (target == typeof(Type) || target == typeof(ResourceType)))
                            {
                                if (WebConvert.TryRemoveQuotes(ref text)) 
                                {
                                    ResourceType resourceType = WebUtil.TryResolveResourceType(this.provider, text); 
                                    if (resourceType != null) 
                                    {
                                        if (target == typeof(Type)) 
                                        {
                                            if (resourceType.CanReflectOnInstanceType == true)
                                            {
                                                value = resourceType.InstanceType; 
                                            }
                                        } 
                                        else 
                                        {
                                            if (resourceType.CanReflectOnInstanceType == false) 
                                            {
                                                value = resourceType;
                                            }
                                        } 
                                    }
                                } 
                            } 
                            else
                            { 
                                switch (Type.GetTypeCode(ce.Type))
                                {
                                    case TypeCode.Int32:
                                    case TypeCode.Int64: 
                                        value = ParseNumber(text, target);
                                        break; 
                                    case TypeCode.Double: 
                                        if (target == typeof(decimal))
                                        { 
                                            value = ParseNumber(text, target);
                                        }

                                        break; 
                                }
                            } 
 
                            if (value != null)
                            { 
                                return Expression.Constant(value, type);
                            }
                        }
                    } 
                }
 
                if (IsCompatibleWith(expr.Type, type)) 
                {
                    if (type.IsValueType || exact) 
                    {
                        return Expression.Convert(expr, type);
                    }
 
                    return expr;
                } 
 
                // Allow promotion from nullable to non-nullable by directly accessing underlying value.
                if (WebUtil.IsNullableType(expr.Type) && type.IsValueType) 
                {
                    Expression valueAccessExpression = Expression.Property(expr, "Value");
                    valueAccessExpression = this.PromoteExpression(valueAccessExpression, type, exact);
                    return valueAccessExpression; 
                }
 
                return null; 
            }
 
            /// Checks that the current token has the specified identifier.
            /// Identifier to check.
            /// true if the current token is an identifier with the specified text.
            private bool TokenIdentifierIs(string id) 
            {
                return this.CurrentToken.IdentifierIs(id); 
            } 

            /// Validates the current token is of the specified kind. 
            /// Expected token kind.
            private void ValidateToken(TokenId t)
            {
                if (this.CurrentToken.Id != t) 
                {
                    throw ParseError(Strings.RequestQueryParser_SyntaxError(this.CurrentToken.Position)); 
                } 
            }
 
            #region Recursion control.

            /// Marks the fact that a recursive method was entered, and checks that the depth is allowed.
            private void RecurseEnter() 
            {
                WebUtil.RecurseEnterQueryParser(RecursionLimit, ref this.recursionDepth); 
            } 

            /// Marks the fact that a recursive method is leaving. 
            private void RecurseLeave()
            {
                WebUtil.RecurseLeave(ref this.recursionDepth);
            } 

            #endregion Recursion control. 
 
            /// Use this class to encapsulate method information.
            [DebuggerDisplay("MethodData {methodBase}")] 
            private class MethodData
            {
                #region Private fields.
 
                /// Described method.
                private readonly MethodBase methodBase; 
 
                /// Parameters for method.
                private readonly ParameterInfo[] parameters; 

                /// Argument expressions.
                private Expression[] args;
 
                #endregion Private fields.
 
                #region Constructors. 

                /// Initializes a new  instance. 
                /// Described method
                /// Parameters for method.
                public MethodData(MethodBase method, ParameterInfo[] parameters)
                { 
                    this.methodBase = method;
                    this.parameters = parameters; 
                } 

                #endregion Constructors. 

                #region Properties.

                /// Argument expressions. 
                public Expression[] Args
                { 
                    get { return this.args; } 
                    set { this.args = value; }
                } 

                /// Described method.
                public MethodBase MethodBase
                { 
                    get { return this.methodBase; }
                } 
 
                /// Parameters for method.
                public ParameterInfo[] Parameters 
                {
                    get { return this.parameters; }
                }
 
                /// Enumeration of parameter types.
                public IEnumerable ParameterTypes 
                { 
                    get
                    { 
                        foreach (ParameterInfo parameter in this.Parameters)
                        {
                            yield return parameter.ParameterType;
                        } 
                    }
                } 
 
                #endregion Properties.
            } 

            /// 
            /// ResourceType and ResourceSet information for current segment.
            /// This is used only when parsing member access paths. 
            /// 
            private class SegmentTypeInfo 
            { 
                /// Constructor.
                /// Type for current segment. 
                /// Set for current segment.
                /// Does current segment property refer to a collection.
                public SegmentTypeInfo(ResourceType resourceType, ResourceSetWrapper resourceSet, bool isCollection)
                { 
                    this.ResourceType = resourceType;
                    this.ResourceSet = resourceSet; 
                    this.IsCollection = isCollection; 
                }
 
                /// Type for the current segment.
                public ResourceType ResourceType
                {
                    get; 
                    private set;
                } 
 
                /// Resource set for the current segment.
                public ResourceSetWrapper ResourceSet 
                {
                    get;
                    private set;
                } 

                /// Does the current segment property refer to a collection. 
                public bool IsCollection 
                {
                    get; 
                    private set;
                }
            }
        } 
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
                        

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