mono/mcs/class/System.Core/System.Linq.Expressions/Expression.cs

//
// Expression.cs
//
// Author:
//   Marek Safar ([email protected])
//   Antonello Provenzano  <[email protected]>
//   Federico Di Gregorio <[email protected]>
//   Jb Evain ([email protected])
//
// (C) 2008 Novell, Inc. (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Reflection;
using System.Text;

namespace System.Linq.Expressions
{
	public abstract class Expression
	{
		Type type;
		ExpressionType nodeType;

		public Type Type {
			get { return type; }
		}

		public ExpressionType NodeType {
			get { return nodeType; }
		}

		protected Expression (ExpressionType nodeType, Type type)
		{
			this.nodeType = nodeType;
			this.type = type;
		}

		#region Internal methods
		internal virtual void BuildString (StringBuilder builder)
		{
			builder.Append ("[").Append (nodeType).Append ("]");
		}

		internal static Type GetNonNullableType(Type type)
		{
			// The Nullable<> class takes a single generic type so we can directly return
			// the first element of the array (if the type is nullable.)

			if (IsNullableType (type))
				return type.GetGenericArguments ()[0];
			else
				return type;
		}

		internal static bool IsNullableType (Type type)
		{
			if (type == null)
				throw new ArgumentNullException ("type");

			return type.IsGenericType && type.GetGenericTypeDefinition () == typeof (Nullable<>);
		}
		#endregion

		#region Private support methods
		private static int IsWhat(Type type)
		{
			// This method return a "type code" that can be easily compared to a bitmask
			// to determine the "broad type" (integer, boolean, floating-point) of the given type.
			// It is used by the three methods below.

			if (IsNullableType (type))
				type = GetNonNullableType (type);

			switch (Type.GetTypeCode (type)) {
				case TypeCode.Byte:  case TypeCode.SByte:
				case TypeCode.Int16: case TypeCode.UInt16:
				case TypeCode.Int32: case TypeCode.UInt32:
				case TypeCode.Int64: case TypeCode.UInt64:
				return 1;

				case TypeCode.Boolean:
				return 2;

				case TypeCode.Single:
				case TypeCode.Double:
				case TypeCode.Decimal:
				return 4;

				default:
				return 0;
			}
		}

		private static bool IsInteger (Type type)
		{
			return (IsWhat(type) & 1) != 0;
		}

		private static bool IsIntegerOrBool (Type type)
		{
			return (IsWhat(type) & 3) != 0;
		}

		private static bool IsNumeric (Type type)
		{
			return (IsWhat(type) & 5) != 0;
		}

		private const BindingFlags opBindingFlags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static;

		private static MethodInfo GetUserDefinedBinaryOperator (Type leftType, Type rightType, string name)
		{
			Type[] types = new Type[2] { leftType, rightType };
			MethodInfo method;

			method  = leftType.GetMethod (name, opBindingFlags, null, types, null);
			if (method != null) return method;

			method = rightType.GetMethod (name, opBindingFlags, null, types, null);
			if (method != null) return method;

			if (method == null && IsNullableType (leftType) && IsNullableType (rightType))
				return GetUserDefinedBinaryOperator (GetNonNullableType (leftType), GetNonNullableType (rightType), name);

			return null;
		}

		private static BinaryExpression GetUserDefinedBinaryOperatorOrThrow (ExpressionType nodeType, string name,
				Expression left, Expression right)
		{
			MethodInfo method = GetUserDefinedBinaryOperator(left.type, right.type, name);

			if (method != null)
				return new BinaryExpression (nodeType, left, right, method, method.ReturnType);
			else
				throw new InvalidOperationException (String.Format (
					"The binary operator Add is not defined for the types '{0}' and '{1}'.", left.type, right.type));

			// Note: here the code in ExpressionUtils has a series of checks to make sure that
			// the method is static, that its return type is not void and that the number of
			// parameters is 2 and they are of the right type, but we already know that! Or not?
		}

		private static MethodInfo FindMethod (Type type, string methodName, Type [] typeArgs, Expression [] args, BindingFlags flags)
		{
			MemberInfo[] members = type.FindMembers(MemberTypes.Method, flags,
				delegate(MemberInfo mi, object obj) { return mi.Name == (String)obj; },
				methodName);
			if (members.Length == 0)
				throw new InvalidOperationException (String.Format (
					"No method '{0}' exists on type '{1}'.", methodName, type.FullName));

			MethodInfo methodDefinition = null;
			MethodInfo method = null;
			int methodCount = 1;

			foreach (MemberInfo member in members) {
				MethodInfo mi = (MethodInfo)member;
				if (mi.IsGenericMethodDefinition) {
					// If the generic method definition matches we save it away to be able to make the
					// correct closed method later on.
					Type[] genericArgs = mi.GetGenericArguments();
					if (genericArgs.Length != typeArgs.Length) goto next;

					methodDefinition = mi;
					goto next;
				}

				// If there is a discrepancy between method's generic types and the given types or if
				// the method is open we simply discard it and go on.
				if ((mi.IsGenericMethod && (typeArgs == null || mi.ContainsGenericParameters))
					 || (!mi.IsGenericMethod && typeArgs != null))
					goto next;

				// If the method is a closed generic we try to match the generic types.
				if (mi.IsGenericMethod) {
					Type[] genericArgs = mi.GetGenericArguments();
					if (genericArgs.Length != typeArgs.Length) goto next;
					for (int i=0 ; i < genericArgs.Length ; i++)
						if (genericArgs[i] != typeArgs[i]) goto next;
				}

				// Finally we test for the method's parameters.
				ParameterInfo[] parameters = mi.GetParameters ();
				if (parameters.Length != args.Length) goto next;
				for (int i=0 ; i < parameters.Length ; i++)
					if (parameters[i].ParameterType != args[i].type) goto next;

				method = mi;
				break;

			 next:
				continue;
			}

			if (method != null)
				return method;
			else
				throw new InvalidOperationException(String.Format(
					"No method '{0}' on type '{1}' is compatible with the supplied arguments.", methodName, type.FullName));
		}

		private static PropertyInfo GetProperty (MethodInfo mi)
		{
			// If the method has the hidebysig and specialname attributes it can be a property accessor;
			// if that's the case we try to extract the type of the property and then we use it and the
			// property name (derived from the method name) to find the right PropertyInfo.

			if (mi.IsHideBySig && mi.IsSpecialName) {
				Type propertyType = null;
				if (mi.Name.StartsWith("set_")) {
					ParameterInfo[] parameters = mi.GetParameters();
					if (parameters.Length == 1)
						propertyType = parameters[0].ParameterType;
				}
				else if (mi.Name.StartsWith("get_")) {
					propertyType = mi.ReturnType;
				}

				if (propertyType != null) {
					PropertyInfo pi = mi.DeclaringType.GetProperty(mi.Name.Substring(4),
						BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Instance,
						null, propertyType, new Type[0], null);
					if (pi != null) return pi;
				}
			}

			throw new ArgumentException (String.Format(
				"The method '{0}.{1}' is not a property accessor", mi.DeclaringType.FullName, mi.Name));
		}

		private static void ValidateUserDefinedConditionalLogicOperator (ExpressionType nodeType, Type left, Type right, MethodInfo method)
		{
			// Conditional logic need the "definitely true" and "definitely false" operators.
			Type[] types = new Type[1] { left };

			MethodInfo opTrue  = left.GetMethod ("op_True", opBindingFlags, null, types, null);
			MethodInfo opFalse = left.GetMethod ("op_False", opBindingFlags, null, types, null);

			if (opTrue == null || opFalse == null)
				throw new ArgumentException (String.Format (
					"The user-defined operator method '{0}' for operator '{1}' must have associated boolean True and False operators.",
					method.Name, nodeType));
		}

		private static void ValidateSettableFieldOrPropertyMember (MemberInfo member, out Type memberType)
		{
			if (member.MemberType == MemberTypes.Field) {
				memberType = (member as FieldInfo).FieldType;
			}
			else if (member.MemberType == MemberTypes.Property) {
				PropertyInfo pi = (PropertyInfo)member;
				if (!pi.CanWrite)
					throw new ArgumentException (String.Format ("The property '{0}' has no 'set' accessor", pi));
				memberType = (member as PropertyInfo).PropertyType;
			}
			else {
				throw new ArgumentException ("Argument must be either a FieldInfo or PropertyInfo");
			}
		}

		private static void ValidateGettableFieldOrPropertyMember (MemberInfo member, out Type memberType)
		{
			if (member.MemberType == MemberTypes.Field) {
				memberType = (member as FieldInfo).FieldType;
			}
			else if (member.MemberType == MemberTypes.Property) {
				PropertyInfo pi = (PropertyInfo)member;
				if (!pi.CanRead)
					throw new ArgumentException (String.Format ("The property '{0}' has no 'get' accessor", pi));
				memberType = (member as PropertyInfo).PropertyType;
			}
			else {
				throw new ArgumentException ("Argument must be either a FieldInfo or PropertyInfo");
			}
		}
		#endregion

		#region ToString
		public override string ToString()
		{
			StringBuilder builder = new StringBuilder ();
			BuildString (builder);
			return builder.ToString ();
		}
		#endregion

		#region Add
		public static BinaryExpression Add(Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression(ExpressionType.Add, left, right, method, method.ReturnType);

			// Since both the expressions define the same numeric type we don't have
			// to look for the "op_Addition" method.
			if (left.type == right.type && IsNumeric (left.type))
				return new BinaryExpression(ExpressionType.Add, left, right, left.type);

			// Else we try for a user-defined operator.
			return GetUserDefinedBinaryOperatorOrThrow (ExpressionType.Add, "op_Addition", left, right);
		}

		public static BinaryExpression Add(Expression left, Expression right)
		{
			return Add(left, right, null);
		}
		#endregion

		#region AddChecked
		public static BinaryExpression AddChecked(Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression(ExpressionType.AddChecked, left, right, method, method.ReturnType);

			// Since both the expressions define the same numeric type we don't have
			// to look for the "op_Addition" method.
			if (left.type == right.type && IsNumeric (left.type))
				return new BinaryExpression(ExpressionType.AddChecked, left, right, left.type);

			method = GetUserDefinedBinaryOperator (left.type, right.type, "op_Addition");
			if (method == null)
				throw new InvalidOperationException(String.Format(
					"The binary operator AddChecked is not defined for the types '{0}' and '{1}'.", left.type, right.type));

			Type retType = method.ReturnType;

			// Note: here the code did some very strange checks for bool (but note that bool does
			// not define an addition operator) and created nullables for value types (but the new
			// MS code does not do that). All that has been removed.

			return new BinaryExpression(ExpressionType.AddChecked, left, right, method, retType);
		}

		public static BinaryExpression AddChecked(Expression left, Expression right)
		{
			return AddChecked(left, right, null);
		}
		#endregion

		#region And
		public static BinaryExpression And(Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression(ExpressionType.And, left, right, method, method.ReturnType);

			// Since both the expressions define the same integer or boolean type we don't have
			// to look for the "op_BitwiseAnd" method.
			if (left.type == right.type && IsIntegerOrBool (left.type))
				return new BinaryExpression(ExpressionType.And, left, right, left.type);

			// Else we try for a user-defined operator.
			return GetUserDefinedBinaryOperatorOrThrow (ExpressionType.And, "op_BitwiseAnd", left, right);
		}

		public static BinaryExpression And(Expression left, Expression right)
		{
			return And(left, right, null);
		}
		#endregion

		#region AndAlso
		public static BinaryExpression AndAlso(Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			// Since both the expressions define the same boolean type we don't have
			// to look for the "op_BitwiseAnd" method.
			if (left.type == right.type && left.type == typeof(bool))
				return new BinaryExpression(ExpressionType.AndAlso, left, right, left.type);

			// Else we must validate the method to make sure it has companion "true" and "false" operators.
			if (method == null)
				method = GetUserDefinedBinaryOperator (left.type, right.type, "op_BitwiseAnd");
			if (method == null)
				throw new InvalidOperationException(String.Format(
					"The binary operator AndAlso is not defined for the types '{0}' and '{1}'.", left.type, right.type));
			ValidateUserDefinedConditionalLogicOperator(ExpressionType.AndAlso, left.type, right.type, method);

			return new BinaryExpression(ExpressionType.AndAlso, left, right, method, method.ReturnType);
		}

		public static BinaryExpression AndAlso(Expression left, Expression right)
		{
			return AndAlso(left, right, null);
		}
		#endregion

		#region ArrayIndex
		public static BinaryExpression ArrayIndex(Expression array, Expression index)
		{
			if (array == null)
				throw new ArgumentNullException ("array");
			if (index == null)
				throw new ArgumentNullException ("index");
			if (!array.type.IsArray)
				throw new ArgumentException ("Argument must be array");
			if (index.type != typeof(int))
				throw new ArgumentException ("Argument for array index must be of type Int32");

			return new BinaryExpression(ExpressionType.ArrayIndex, array, index, array.type.GetElementType());
		}

		public static MethodCallExpression ArrayIndex(Expression array, params Expression[] indexes)
		{
			return ArrayIndex(array, (IEnumerable<Expression>)indexes);
		}

		public static MethodCallExpression ArrayIndex(Expression array, IEnumerable<Expression> indexes)
		{
			if (array == null)
				throw new ArgumentNullException ("array");
			if (indexes == null)
				throw new ArgumentNullException ("indexes");
			if (!array.type.IsArray)
				throw new ArgumentException ("Argument must be array");

			// We'll need an array of typeof(Type) elements long as the array's rank later
			// and also a generic List to hold the indexes (ReadOnlyCollection wants that.)

			Type[] types = (Type[])Array.CreateInstance(typeof(Type), array.type.GetArrayRank());
			Expression[] indexesList = new Expression[array.type.GetArrayRank()];

			int rank = 0;
			foreach (Expression index in indexes) {
				if (index.type != typeof(int))
					throw new ArgumentException ("Argument for array index must be of type Int32");
				if (rank == array.type.GetArrayRank())
					throw new ArgumentException ("Incorrect number of indexes");

				types[rank] = index.type;
				indexesList[rank] = index;
				rank += 1;
			}

			// If the array's rank is equalto the number of given indexes we can go on and
			// look for a Get(Int32, ...) method with "rank" parameters to generate the
			// MethodCallExpression.

			MethodInfo method = array.type.GetMethod("Get",
				BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance, null, types, null);

			// This should not happen, but we check anyway.
			if (method == null)
				throw new InvalidOperationException(String.Format(
					"The method Get(...) is not defined for the type '{0}'.", array.type));

			return new MethodCallExpression(ExpressionType.Call, method, array, new ReadOnlyCollection<Expression>(indexesList));
		}
		#endregion

		#region ArrayLength
		public static UnaryExpression ArrayLength (Expression array)
		{
			if (array == null)
				throw new ArgumentNullException ("array");
			if (!array.type.IsArray)
				throw new ArgumentException ("Argument must be array");
			if (array.type.GetArrayRank () != 1)
				throw new ArgumentException ("Argument must be a single dimensional array");

			return new UnaryExpression (ExpressionType.ArrayLength, array, typeof (int));
		}
		#endregion

		#region Bind
		public static MemberAssignment Bind (MemberInfo member, Expression expression)
		{
			if (member == null)
				throw new ArgumentNullException ("member");
			if (expression == null)
				throw new ArgumentNullException ("expression");

			Type memberType;
			ValidateSettableFieldOrPropertyMember(member, out memberType);

			return new MemberAssignment(member, expression);
		}

		public static MemberAssignment Bind (MethodInfo propertyAccessor, Expression expression)
		{
			if (propertyAccessor == null)
				throw new ArgumentNullException ("propertyAccessor");
			if (expression == null)
				throw new ArgumentNullException ("expression");

			return new MemberAssignment(GetProperty(propertyAccessor), expression);
		}
		#endregion

		#region Call
		public static MethodCallExpression Call(Expression instance, MethodInfo method)
		{
			if (method == null)
				throw new ArgumentNullException("method");
			if (instance == null && !method.IsStatic)
				throw new ArgumentNullException("instance");

			return Call(instance, method, (Expression[])null);
		}

		public static MethodCallExpression Call(Expression instance, MethodInfo method, params Expression[] arguments)
		{
			return Call(instance, method, (IEnumerable<Expression>)arguments);
		}

		public static MethodCallExpression Call(Expression instance, MethodInfo method, IEnumerable<Expression> arguments)
		{
			if (method == null)
				throw new ArgumentNullException("method");
			if (arguments == null)
				throw new ArgumentNullException("arguments");
			if (instance == null && !method.IsStatic)
				throw new ArgumentNullException("instance");

			if (method.IsGenericMethodDefinition)
					throw new ArgumentException();
			if (method.ContainsGenericParameters)
					throw new ArgumentException();
			if (instance != null && !instance.type.IsAssignableFrom(method.DeclaringType))
				throw new ArgumentException();

			ReadOnlyCollection<Expression> roArgs = Enumerable.ToReadOnlyCollection<Expression>(arguments);

			ParameterInfo[] pars = method.GetParameters();
			if (Enumerable.Count<Expression>(arguments) != pars.Length)
				throw new ArgumentException();

			if (pars.Length > 0)
			{
				//TODO: validate the parameters against the arguments...
			}

			return new MethodCallExpression(ExpressionType.Call, method, instance, roArgs);
		}

		public static MethodCallExpression Call (Expression instance, string methodName, Type [] typeArguments, params Expression [] arguments)
		{
			if (instance == null)
				throw new ArgumentNullException("instance");
			if (arguments == null)
				throw new ArgumentNullException("arguments");

			return Call (null, FindMethod (instance.type, methodName, typeArguments, arguments,
					BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Instance),
				(IEnumerable<Expression>)arguments);
		}

		public static MethodCallExpression Call(MethodInfo method, params Expression[] arguments)
		{
			return Call(null, method, (IEnumerable<Expression>)arguments);
		}

		public static MethodCallExpression Call (Type type, string methodName, Type [] typeArguments, params Expression [] arguments)
		{
			if (type == null)
				throw new ArgumentNullException ("type");
			if (methodName == null)
				throw new ArgumentNullException ("methodName");
			if (arguments == null)
				throw new ArgumentNullException ("arguments");

			// Note that we're looking for static methods only (this version of Call() doesn't take an instance).
			return Call (null, FindMethod (type, methodName, typeArguments, arguments,
					BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static),
				(IEnumerable<Expression>)arguments);
		}
		#endregion

		// NOTE: CallVirtual is not implemented because it is already marked as Obsolete by MS.

		public static ConditionalExpression Condition(Expression test, Expression ifTrue, Expression ifFalse)
		{
			if (test == null)
				throw new ArgumentNullException("test");
			if (ifTrue == null)
				throw new ArgumentNullException("ifTrue");
			if (ifFalse == null)
				throw new ArgumentNullException("ifFalse");
			if (test.type != typeof(bool))
				throw new ArgumentException();
			if (ifTrue.type != ifFalse.type)
				throw new ArgumentException();

			return new ConditionalExpression(test, ifTrue, ifFalse, ifTrue.type);
		}

		public static ConstantExpression Constant(object value, Type type)
		{
			if (type == null)
				throw new ArgumentNullException("type");
			if (value == null && !IsNullableType(type))
				throw new ArgumentException("Argument types do not match");

			return new ConstantExpression(value, type);
		}

		public static ConstantExpression Constant(object value)
		{
			if (value != null)
				return new ConstantExpression(value, value.GetType());
			else
				return new ConstantExpression(null, typeof(object));
		}

		#region Divide
		public static BinaryExpression Divide(Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression(ExpressionType.Divide, left, right, method, method.ReturnType);

			// Since both the expressions define the same numeric type we don't have
			// to look for the "op_Addition" method.
			if (left.type == right.type && IsNumeric (left.type))
				return new BinaryExpression(ExpressionType.Divide, left, right, left.type);

			// Else we try for a user-defined operator.
			return GetUserDefinedBinaryOperatorOrThrow (ExpressionType.Divide, "op_Division", left, right);
		}

		public static BinaryExpression Divide(Expression left, Expression right)
		{
			return Divide(left, right, null);
		}
		#endregion

		#region ExclusiveOr
		public static BinaryExpression ExclusiveOr (Expression left, Expression right, System.Reflection.MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression(ExpressionType.ExclusiveOr, left, right, method, method.ReturnType);

			// Since both the expressions define the same integer or boolean type we don't have
			// to look for the "op_BitwiseAnd" method.
			if (left.type == right.type && IsIntegerOrBool (left.type))
				return new BinaryExpression(ExpressionType.ExclusiveOr, left, right, left.type);

			// Else we try for a user-defined operator.
			return GetUserDefinedBinaryOperatorOrThrow (ExpressionType.ExclusiveOr, "op_ExclusiveOr", left, right);
		}

		public static BinaryExpression ExclusiveOr (Expression left, Expression right)
		{
			return ExclusiveOr (left, right, null);
		}
		#endregion

		#region Field
		public static MemberExpression Field (Expression expression, FieldInfo field)
		{
			// Note that expression can be (and should be) null when the access is to a static field.

			if (field == null)
				throw new ArgumentNullException("field");

			Type fieldType;
			ValidateGettableFieldOrPropertyMember(field, out fieldType);

			return new MemberExpression(expression, field, fieldType);
		}

		public static MemberExpression Field (Expression expression, string fieldName)
		{
			if (expression == null)
				throw new ArgumentNullException("expression");
			if (fieldName == null)
				throw new ArgumentNullException("fieldName");

			FieldInfo field = expression.Type.GetField(fieldName,
				BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
			if (field == null)
				throw new ArgumentException (String.Format ("Field {0} is not defined for type {1}",
					fieldName, expression.type.FullName));

			return Field(expression, field);
		}
		#endregion

		public static Type GetActionType (params Type [] typeArgs)
		{
			if (typeArgs == null)
				throw new ArgumentNullException ("typeArgs");

			if (typeArgs.Length > 4)
				throw new ArgumentException ("No Action type of this arity");

			if (typeArgs.Length == 0)
				return typeof (Action);

			Type action = null;
			switch (typeArgs.Length) {
			case 1:
				action = typeof (Action<>);
				break;
			case 2:
				action = typeof (Action<,>);
				break;
			case 3:
				action = typeof (Action<,,>);
				break;
			case 4:
				action = typeof (Action<,,,>);
				break;
			}

			return action.MakeGenericType (typeArgs);
		}

		public static Type GetFuncType (params Type [] typeArgs)
		{
			if (typeArgs == null)
				throw new ArgumentNullException ("typeArgs");

			if (typeArgs.Length < 1 || typeArgs.Length > 5)
				throw new ArgumentException ("No Func type of this arity");

			Type func = null;
			switch (typeArgs.Length) {
			case 1:
				func = typeof (Func<>);
				break;
			case 2:
				func = typeof (Func<,>);
				break;
			case 3:
				func = typeof (Func<,,>);
				break;
			case 4:
				func = typeof (Func<,,,>);
				break;
			case 5:
				func = typeof (Func<,,,,>);
				break;
			}

			return func.MakeGenericType (typeArgs);
		}

		#region LeftShift
		public static BinaryExpression LeftShift (Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression(ExpressionType.LeftShift, left, right, method, method.ReturnType);

			// If the left side is any kind of integer and the right is int32 we don't have
			// to look for the "op_Addition" method.
			if (IsInteger(left.type) && right.type == typeof(Int32))
				return new BinaryExpression(ExpressionType.LeftShift, left, right, left.type);

			// Else we try for a user-defined operator.
			return GetUserDefinedBinaryOperatorOrThrow (ExpressionType.LeftShift, "op_LeftShift", left, right);
		}

		public static BinaryExpression LeftShift (Expression left, Expression right)
		{
			return LeftShift (left, right, null);
		}
		#endregion

		public static ListInitExpression ListInit(NewExpression newExpression, params ElementInit[] initializers)
		{
			if (initializers == null)
				throw new ArgumentNullException("inizializers");

			return ListInit(newExpression, Enumerable.ToReadOnlyCollection<ElementInit>(initializers));
		}

		public static ListInitExpression ListInit(NewExpression newExpression, IEnumerable<ElementInit> initializers)
		{
			if (newExpression == null)
				throw new ArgumentNullException("newExpression");
			if (initializers == null)
				throw new ArgumentNullException("inizializers");

			return new ListInitExpression(newExpression, Enumerable.ToReadOnlyCollection<ElementInit>(initializers));
		}

		public static MemberInitExpression MemberInit(NewExpression newExpression, IEnumerable<MemberBinding> bindings)
		{
			if (newExpression == null)
				throw new ArgumentNullException("newExpression");

			if (bindings == null)
				throw new ArgumentNullException("bindings");

			return new MemberInitExpression(newExpression, Enumerable.ToReadOnlyCollection<MemberBinding>(bindings));
		}

		#region Modulo
		public static BinaryExpression Modulo (Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression(ExpressionType.Modulo, left, right, method, method.ReturnType);

			// Since both the expressions define the same integer or boolean type we don't have
			// to look for the "op_BitwiseAnd" method.
			if (left.type == right.type && IsNumeric (left.type))
				return new BinaryExpression(ExpressionType.Modulo, left, right, left.type);

			// Else we try for a user-defined operator.
			return GetUserDefinedBinaryOperatorOrThrow (ExpressionType.Modulo, "op_Modulus", left, right);

		}

		public static BinaryExpression Modulo (Expression left, Expression right)
		{
			return Modulo (left, right, null);
		}
		#endregion

		#region Multiply
		public static BinaryExpression Multiply (Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression(ExpressionType.Multiply, left, right, method, method.ReturnType);

			// Since both the expressions define the same integer or boolean type we don't have
			// to look for the "op_BitwiseAnd" method.
			if (left.type == right.type && IsNumeric (left.type))
				return new BinaryExpression(ExpressionType.Multiply, left, right, left.type);

			// Else we try for a user-defined operator.
			return GetUserDefinedBinaryOperatorOrThrow (ExpressionType.Multiply, "op_Multiply", left, right);

		}

		public static BinaryExpression Multiply (Expression left, Expression right)
		{
			return Multiply (left, right, null);
		}
		#endregion

		#region MultiplyChecked
		public static BinaryExpression MultiplyChecked (Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression(ExpressionType.MultiplyChecked, left, right, method, method.ReturnType);

			// Since both the expressions define the same numeric type we don't have
			// to look for the "op_Addition" method.
			if (left.type == right.type && IsNumeric (left.type))
				return new BinaryExpression(ExpressionType.MultiplyChecked, left, right, left.type);

			method = GetUserDefinedBinaryOperator (left.type, right.type, "op_Multiply");
			if (method == null)
				throw new InvalidOperationException(String.Format(
					"The binary operator MultiplyChecked is not defined for the types '{0}' and '{1}'.", left.type, right.type));

			Type retType = method.ReturnType;

			return new BinaryExpression(ExpressionType.MultiplyChecked, left, right, method, retType);
		}

		public static BinaryExpression MultiplyChecked (Expression left, Expression right)
		{
			return MultiplyChecked(left, right, null);
		}
		#endregion

		#region Or
		public static BinaryExpression Or (Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression(ExpressionType.Or, left, right, method, method.ReturnType);

			// Since both the expressions define the same integer or boolean type we don't have
			// to look for the "op_BitwiseOr" method.
			if (left.type == right.type && IsIntegerOrBool (left.type))
				return new BinaryExpression(ExpressionType.Or, left, right, left.type);

			// Else we try for a user-defined operator.
			return GetUserDefinedBinaryOperatorOrThrow (ExpressionType.Or, "op_BitwiseOr", left, right);

		}

		public static BinaryExpression Or (Expression left, Expression right)
		{
			return Or (left, right, null);
		}
		#endregion

		#region OrElse
		public static BinaryExpression OrElse (Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			// Since both the expressions define the same boolean type we don't have
			// to look for the "op_BitwiseOr" method.
			if (left.type == right.type && left.type == typeof(bool))
				return new BinaryExpression(ExpressionType.OrElse, left, right, left.type);

			// Else we must validate the method to make sure it has companion "true" and "false" operators.
			if (method == null)
				method = GetUserDefinedBinaryOperator (left.type, right.type, "op_BitwiseOr");
			if (method == null)
				throw new InvalidOperationException(String.Format(
					"The binary operator OrElse is not defined for the types '{0}' and '{1}'.", left.type, right.type));
			ValidateUserDefinedConditionalLogicOperator(ExpressionType.OrElse, left.type, right.type, method);

			return new BinaryExpression(ExpressionType.OrElse, left, right, method, method.ReturnType);
		}

		public static BinaryExpression OrElse (Expression left, Expression right)
		{
			return OrElse(left, right, null);
		}
		#endregion

		#region Property
		public static MemberExpression Property (Expression expression, MethodInfo propertyAccessor)
		{
			if (propertyAccessor == null)
				throw new ArgumentNullException("propertyAccessor");

			return Property(expression, GetProperty(propertyAccessor));
		}

		public static MemberExpression Property (Expression expression, PropertyInfo property)
		{
			if (property == null)
				throw new ArgumentNullException("property");

			Type propertyType;
			ValidateGettableFieldOrPropertyMember(property, out propertyType);

			return new MemberExpression(expression, property, propertyType);
		}


		public static MemberExpression Property(Expression expression, string propertyName)
		{
			if (expression == null)
				throw new ArgumentNullException ("expression");
			if (propertyName == null)
				throw new ArgumentNullException ("propertyName");

			PropertyInfo property = expression.Type.GetProperty (propertyName,
				BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);

			if (property == null)
				throw new ArgumentException (String.Format ("{0} is not a member of type {1}",
					propertyName, expression.type.FullName));

			return Property (expression, property);
		}
		#endregion

		#region PropertyOrField
		public static MemberExpression PropertyOrField(Expression expression, string propertyOrFieldName)
		{
			if (expression == null)
				throw new ArgumentNullException ("expression");
			if (propertyOrFieldName == null)
				throw new ArgumentNullException ("propertyOrFieldName");

			PropertyInfo property = expression.type.GetProperty (propertyOrFieldName,
				BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
			if (property != null)
				return Property (expression, property);

			FieldInfo field = expression.type.GetField (propertyOrFieldName,
				BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
			if (field != null)
				return Field (expression, field);

			throw new ArgumentException (String.Format ("{0} is not a member of type {1}",
				propertyOrFieldName, expression.type.FullName));
		}
		#endregion

		#region Quote
		public static UnaryExpression Quote(Expression expression)
		{
			if (expression == null)
				throw new ArgumentNullException ("expression");

			return new UnaryExpression (ExpressionType.Quote, expression, expression.GetType());

		}
		#endregion

		#region RightShift
		public static BinaryExpression RightShift (Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression (ExpressionType.RightShift, left, right, method, method.ReturnType);

			// If the left side is any kind of integer and the right is int32 we don't have
			// to look for the "op_Addition" method.
			if (IsInteger(left.type) && right.type == typeof(Int32))
				return new BinaryExpression (ExpressionType.RightShift, left, right, left.type);

			// Else we try for a user-defined operator.
			return GetUserDefinedBinaryOperatorOrThrow (ExpressionType.RightShift, "op_RightShift", left, right);
		}

		public static BinaryExpression RightShift (Expression left, Expression right)
		{
			return RightShift (left, right, null);
		}
		#endregion

		#region Subtract
		public static BinaryExpression Subtract (Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression (ExpressionType.Subtract, left, right, method, method.ReturnType);

			// Since both the expressions define the same numeric type we don't have
			// to look for the "op_Addition" method.
			if (left.type == right.type && IsNumeric (left.type))
				return new BinaryExpression (ExpressionType.Subtract, left, right, left.type);

			// Else we try for a user-defined operator.
			return GetUserDefinedBinaryOperatorOrThrow (ExpressionType.Subtract, "op_Subtraction", left, right);
		}

		public static BinaryExpression Subtract (Expression left, Expression right)
		{
			return Subtract (left, right, null);
		}
		#endregion

		#region SubtractChecked
		public static BinaryExpression SubtractChecked (Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null)
				return new BinaryExpression (ExpressionType.SubtractChecked, left, right, method, method.ReturnType);

			// Since both the expressions define the same numeric type we don't have
			// to look for the "op_Addition" method.
			if (left.type == right.type && IsNumeric (left.type))
				return new BinaryExpression (ExpressionType.SubtractChecked, left, right, left.type);

			method = GetUserDefinedBinaryOperator (left.type, right.type, "op_Subtraction");
			if (method == null)
				throw new InvalidOperationException (String.Format (
					"The binary operator AddChecked is not defined for the types '{0}' and '{1}'.", left.type, right.type));

			Type retType = method.ReturnType;

			return new BinaryExpression (ExpressionType.SubtractChecked, left, right, method, retType);
		}

		public static BinaryExpression SubtractChecked (Expression left, Expression right)
		{
			return SubtractChecked (left, right, null);
		}
		#endregion

		#region TypeAs
		public static UnaryExpression TypeAs (Expression expression, Type type)
		{
			if (expression == null)
				throw new ArgumentNullException ("expression");
			if (type == null)
				throw new ArgumentNullException ("type");
			if (type.IsValueType && !IsNullableType (type))
				throw new ArgumentException ("Reference or nullable type expected");

			return new UnaryExpression (ExpressionType.TypeAs, expression, type);
		}
		#endregion

		#region TypeIs
		public static TypeBinaryExpression TypeIs (Expression expression, Type type)
		{
			if (expression == null)
				throw new ArgumentNullException ("expression");
			if (type == null)
				throw new ArgumentNullException ("type");

			return new TypeBinaryExpression (ExpressionType.TypeIs, expression, type, typeof(bool));
		}
		#endregion

		[MonoTODO]
		public static Expression<TDelegate> Lambda<TDelegate> (Expression body, params ParameterExpression [] parameters)
		{
			throw new NotImplementedException ();
		}

		[MonoTODO]
		public static Expression<TDelegate> Lambda<TDelegate> (Expression body, IEnumerable<ParameterExpression> parameters)
		{
			throw new NotImplementedException ();
		}

		[MonoTODO]
		public static LambdaExpression Lambda (Expression body, params ParameterExpression [] parameters)
		{
			throw new NotImplementedException ();
		}

		[MonoTODO]
		public static LambdaExpression Lambda (Type delegateType, Expression body, params ParameterExpression [] parameters)
		{
			throw new NotImplementedException ();
		}

		[MonoTODO]
		public static LambdaExpression Lambda (Type delegateType, Expression body, IEnumerable<ParameterExpression> parameters)
		{
			throw new NotImplementedException ();
		}
	}
}