//
// Expression.cs
//
// Author:
//   Jb Evain (jbevain@novell.com)
//   Miguel de Icaza (miguel@novell.com)
//
// (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;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Globalization;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;

namespace System.Linq.Expressions {

	public abstract class Expression {

		ExpressionType node_type;
		Type type;

		internal const BindingFlags PublicInstance = BindingFlags.Public | BindingFlags.Instance | BindingFlags.FlattenHierarchy;
		internal const BindingFlags NonPublicInstance = BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.FlattenHierarchy;
		internal const BindingFlags PublicStatic = BindingFlags.Public | BindingFlags.Static | BindingFlags.FlattenHierarchy;
		internal const BindingFlags AllInstance = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.FlattenHierarchy;
		internal const BindingFlags AllStatic = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.FlattenHierarchy;
		internal const BindingFlags All = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Instance | BindingFlags.FlattenHierarchy;

		public ExpressionType NodeType {
			get { return node_type; }
		}

		public Type Type {
			get { return type; }
		}

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

		public override string ToString ()
		{
			return ExpressionPrinter.ToString (this);
		}

		#region Binary Expressions

		static MethodInfo GetUnaryOperator (string oper_name, Type declaring, Type param)
		{
			return GetUnaryOperator (oper_name, declaring, param, null);
		}

		static MethodInfo GetUnaryOperator (string oper_name, Type declaring, Type param, Type ret)
		{
			var methods = declaring.GetNotNullableType ().GetMethods (PublicStatic);

			foreach (var method in methods) {
				if (method.Name != oper_name)
					continue;

				var parameters = method.GetParameters ();
				if (parameters.Length != 1)
					continue;

				if (method.IsGenericMethod)
					continue;

				if (!IsAssignableToParameterType (param.GetNotNullableType (), parameters [0]))
					continue;

				if (ret != null && method.ReturnType != ret.GetNotNullableType ())
					continue;

				return method;
			}

			return null;
		}

		internal static MethodInfo GetTrueOperator (Type self)
		{
			return GetBooleanOperator ("op_True", self);
		}

		internal static MethodInfo GetFalseOperator (Type self)
		{
			return GetBooleanOperator ("op_False", self);
		}

		static MethodInfo GetBooleanOperator (string op, Type self)
		{
			return GetUnaryOperator (op, self, self, typeof (bool));
		}

		static bool IsAssignableToParameterType (Type type, ParameterInfo param)
		{
			var ptype = param.ParameterType;
			if (ptype.IsByRef)
				ptype = ptype.GetElementType ();

			return type.GetNotNullableType ().IsAssignableTo (ptype);
		}

		static MethodInfo CheckUnaryMethod (MethodInfo method, Type param)
		{
			if (method.ReturnType == typeof (void))
				throw new ArgumentException ("Specified method must return a value", "method");

			if (!method.IsStatic)
				throw new ArgumentException ("Method must be static", "method");

			var parameters = method.GetParameters ();

			if (parameters.Length != 1)
				throw new ArgumentException ("Must have only one parameters", "method");

			if (!IsAssignableToParameterType (param.GetNotNullableType (), parameters [0]))
				throw new InvalidOperationException ("left-side argument type does not match expression type");

			return method;
		}

		static MethodInfo UnaryCoreCheck (string oper_name, Expression expression, MethodInfo method, Func<Type, bool> validator)
		{
			if (expression == null)
				throw new ArgumentNullException ("expression");

			if (method != null)
				return CheckUnaryMethod (method, expression.Type);

			var type = expression.Type.GetNotNullableType ();

				if (validator (type))
					return null;

				if (oper_name != null) {
					method = GetUnaryOperator (oper_name, type, expression.Type);
					if (method != null)
						return method;
				}

				throw new InvalidOperationException (
					string.Format ("Operation {0} not defined for {1}", oper_name != null ? oper_name.Substring (3) : "is", expression.Type));
		}

		static MethodInfo GetBinaryOperator (string oper_name, Type on_type, Expression left, Expression right)
		{
			MethodInfo [] methods = on_type.GetMethods (PublicStatic);

			foreach (var method in methods) {
				if (method.Name != oper_name)
					continue;

				var parameters = method.GetParameters ();
				if (parameters.Length != 2)
					continue;

				if (method.IsGenericMethod)
					continue;

				if (!IsAssignableToParameterType (left.Type, parameters [0]))
					continue;

				if (!IsAssignableToParameterType (right.Type, parameters [1]))
					continue;

				// Method has papers in order.
				return method;
			}

			return null;
		}

		//
		// Performs basic checks on the incoming expressions for binary expressions
		// and any provided MethodInfo.
		//
		static MethodInfo BinaryCoreCheck (string oper_name, Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method != null){
				if (method.ReturnType == typeof (void))
					throw new ArgumentException ("Specified method must return a value", "method");

				if (!method.IsStatic)
					throw new ArgumentException ("Method must be static", "method");

				var parameters = method.GetParameters ();

				if (parameters.Length != 2)
					throw new ArgumentException ("Must have only two parameters", "method");

				if (!IsAssignableToParameterType (left.Type, parameters [0]))
					throw new InvalidOperationException ("left-side argument type does not match left expression type");

				if (!IsAssignableToParameterType (right.Type, parameters [1]))
					throw new InvalidOperationException ("right-side argument type does not match right expression type");

				return method;
			} else {
				Type ltype = left.Type;
				Type rtype = right.Type;
				Type ultype = ltype.GetNotNullableType ();
				Type urtype = rtype.GetNotNullableType ();

				if (oper_name == "op_BitwiseOr" || oper_name == "op_BitwiseAnd") {
					if (ultype == typeof (bool)) {
						if (ultype == urtype && ltype == rtype)
							return null;
					}
				}

				// Use IsNumber to avoid expensive reflection.
				if (IsNumber (ultype)) {
					if (ultype == urtype && ltype == rtype)
						return null;

					if (oper_name != null){
						method = GetBinaryOperator (oper_name, urtype, left, right);
						if (method != null)
							return method;
					}
				}

				if (oper_name != null){
					method = GetBinaryOperator (oper_name, ultype, left, right);
					if (method != null)
						return method;
				}

				if (oper_name == "op_Equality" || oper_name == "op_Inequality") {
					//
					// == and != allow reference types without operators defined.
					//
					if (!ltype.IsValueType && !rtype.IsValueType)
						return null;

					if (ltype == rtype && ultype.IsEnum)
						return null;

					if (ltype == rtype && ultype == typeof (bool))
						return null;
				}

				if (oper_name == "op_LeftShift" || oper_name == "op_RightShift") {
					if (IsInt (ultype) && urtype == typeof (int))
						return null;
				}

				throw new InvalidOperationException (
					String.Format ("Operation {0} not defined for {1} and {2}", oper_name != null ? oper_name.Substring (3) : "is", ltype, rtype));
			}
		}

		//
		// This is like BinaryCoreCheck, but if no method is used adds the restriction that
		// only ints and bools are allowed
		//
		static MethodInfo BinaryBitwiseCoreCheck (string oper_name, Expression left, Expression right, MethodInfo method)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			if (method == null) {
				// avoid reflection shortcut and catches Ints/bools before we check Numbers in general
				if (left.Type == right.Type && IsIntOrBool (left.Type))
					return null;
			}

			method = BinaryCoreCheck (oper_name, left, right, method);
			if (method == null) {
				// The check in BinaryCoreCheck allows a bit more than we do
				// (floats and doubles).  Catch this here
				if (left.Type == typeof (double) || left.Type == typeof (float))
					throw new InvalidOperationException ("Types not supported");
			}

			return method;
		}

		static BinaryExpression MakeSimpleBinary (ExpressionType et, Expression left, Expression right, MethodInfo method)
		{
			bool is_lifted;
			Type type;

			if (method == null) {
				is_lifted = left.Type.IsNullable ();
				type = left.Type;
			} else {
				var parameters = method.GetParameters ();

				var lp = parameters [0];
				var rp = parameters [1];

				if (IsAssignableToOperatorParameter (left, lp) && IsAssignableToOperatorParameter (right, rp)) {
					is_lifted = false;
					type = method.ReturnType;
				} else if (left.Type.IsNullable ()
					&& right.Type.IsNullable ()
					&& left.Type.GetNotNullableType () == lp.ParameterType
					&& right.Type.GetNotNullableType () == rp.ParameterType
					&& !method.ReturnType.IsNullable ()) {

					is_lifted = true;
					type = method.ReturnType.MakeNullableType ();
				} else
					throw new InvalidOperationException ();
			}

			return new BinaryExpression (et, type, left, right, is_lifted, is_lifted, method, null);
		}

		static bool IsAssignableToOperatorParameter (Expression expression, ParameterInfo parameter)
		{
			if (expression.Type == parameter.ParameterType)
				return true;

			if ((!expression.Type.IsNullable () && !parameter.ParameterType.IsNullable ())
				&& IsAssignableToParameterType (expression.Type, parameter))
				return true;

			return false;
		}

		static UnaryExpression MakeSimpleUnary (ExpressionType et, Expression expression, MethodInfo method)
		{
			bool is_lifted;
			Type type;

			if (method == null) {
				type = expression.Type;
				is_lifted = type.IsNullable ();
			} else {
				var parameter = method.GetParameters () [0];

				if (IsAssignableToOperatorParameter (expression, parameter)) {
					is_lifted = false;
					type = method.ReturnType;
				} else if (expression.Type.IsNullable ()
					&& expression.Type.GetNotNullableType () == parameter.ParameterType
					&& !method.ReturnType.IsNullable ()) {

					is_lifted = true;
					type = method.ReturnType.MakeNullableType ();
				} else
					throw new InvalidOperationException ();
			}

			return new UnaryExpression (et, expression, type, method, is_lifted);
		}

		static BinaryExpression MakeBoolBinary (ExpressionType et, Expression left, Expression right, bool liftToNull, MethodInfo method)
		{
			bool is_lifted;
			Type type;

			if (method == null) {
				if (!left.Type.IsNullable () && !right.Type.IsNullable ()) {
					is_lifted = false;
					liftToNull = false;
					type = typeof (bool);
				} else if (left.Type.IsNullable () && right.Type.IsNullable ()) {
					is_lifted = true;
					type = liftToNull ? typeof (bool?) : typeof (bool);
				} else
					throw new InvalidOperationException ();
			} else {
				var parameters = method.GetParameters ();

				var lp = parameters [0];
				var rp = parameters [1];

				if (IsAssignableToOperatorParameter (left, lp) && IsAssignableToOperatorParameter (right, rp)) {
					is_lifted = false;
					liftToNull = false;
					type = method.ReturnType;
				} else if (left.Type.IsNullable ()
					&& right.Type.IsNullable ()
					&& left.Type.GetNotNullableType () == lp.ParameterType
					&& right.Type.GetNotNullableType () == rp.ParameterType) {

					is_lifted = true;

					if (method.ReturnType == typeof (bool))
						type = liftToNull ? typeof (bool?) : typeof (bool);
					else if (!method.ReturnType.IsNullable ()) {
						//
						// This behavior is not documented: what
						// happens if the result is not typeof(bool), but
						// the parameters are nullable: the result
						// becomes nullable<returntype>
						//
						// See:
						// https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=323139

						type = method.ReturnType.MakeNullableType ();
					} else
						throw new InvalidOperationException ();
				} else
					throw new InvalidOperationException ();
			}

			return new BinaryExpression (et, type, left, right, liftToNull, is_lifted, method, null);
		}

		//
		// Arithmetic
		//
		public static BinaryExpression Add (Expression left, Expression right)
		{
			return Add (left, right, null);
		}

		public static BinaryExpression Add (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_Addition", left, right, method);

			return MakeSimpleBinary (ExpressionType.Add, left, right, method);
		}

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

		public static BinaryExpression AddChecked (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_Addition", left, right, method);

			// The check in BinaryCoreCheck allows a bit more than we do
			// (byte, sbyte).  Catch that here
			if (method == null) {
				if (left.Type == typeof (byte) || left.Type == typeof (sbyte))
					throw new InvalidOperationException (String.Format ("AddChecked not defined for {0} and {1}", left.Type, right.Type));
			}

			return MakeSimpleBinary (ExpressionType.AddChecked, left, right, method);
		}

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

		public static BinaryExpression Subtract (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_Subtraction", left, right, method);

			return MakeSimpleBinary (ExpressionType.Subtract, left, right, method);
		}

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

		public static BinaryExpression SubtractChecked (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_Subtraction", left, right, method);

			// The check in BinaryCoreCheck allows a bit more than we do
			// (byte, sbyte).  Catch that here
			if (method == null) {
				if (left.Type == typeof (byte) || left.Type == typeof (sbyte))
					throw new InvalidOperationException (String.Format ("SubtractChecked not defined for {0} and {1}", left.Type, right.Type));
			}

			return MakeSimpleBinary (ExpressionType.SubtractChecked, left, right, method);
		}

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

		public static BinaryExpression Modulo (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_Modulus", left, right, method);

			return MakeSimpleBinary (ExpressionType.Modulo, left, right, method);
		}

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

		public static BinaryExpression Multiply (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_Multiply", left, right, method);

			return MakeSimpleBinary (ExpressionType.Multiply, left, right, method);
		}

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

		public static BinaryExpression MultiplyChecked (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_Multiply", left, right, method);

			return MakeSimpleBinary (ExpressionType.MultiplyChecked, left, right, method);
		}

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

		public static BinaryExpression Divide (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_Division", left, right, method);

			return MakeSimpleBinary (ExpressionType.Divide, left, right, method);
		}

		public static BinaryExpression Power (Expression left, Expression right)
		{
			return Power (left, right, null);
		}

		public static BinaryExpression Power (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryCoreCheck (null, left, right, method);

			if (left.Type.GetNotNullableType () != typeof (double))
				throw new InvalidOperationException ("Power only supports double arguments");

			return MakeSimpleBinary (ExpressionType.Power, left, right, method);
		}

		//
		// Bitwise
		//
		public static BinaryExpression And (Expression left, Expression right)
		{
			return And (left, right, null);
		}

		public static BinaryExpression And (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryBitwiseCoreCheck ("op_BitwiseAnd", left, right, method);

			return MakeSimpleBinary (ExpressionType.And, left, right, method);
		}

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

		public static BinaryExpression Or (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryBitwiseCoreCheck ("op_BitwiseOr", left, right, method);

			return MakeSimpleBinary (ExpressionType.Or, left, right, method);
		}

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

		public static BinaryExpression ExclusiveOr (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryBitwiseCoreCheck ("op_ExclusiveOr", left, right, method);

			return MakeSimpleBinary (ExpressionType.ExclusiveOr, left, right, method);
		}

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

		public static BinaryExpression LeftShift (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryBitwiseCoreCheck ("op_LeftShift", left, right, method);

			return MakeSimpleBinary (ExpressionType.LeftShift, left, right, method);
		}

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

		public static BinaryExpression RightShift (Expression left, Expression right, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_RightShift", left, right, method);

			return MakeSimpleBinary (ExpressionType.RightShift, left, right, method);
		}

		//
		// Short-circuit
		//
		public static BinaryExpression AndAlso (Expression left, Expression right)
		{
			return AndAlso (left, right, null);
		}

		public static BinaryExpression AndAlso (Expression left, Expression right, MethodInfo method)
		{
			method = ConditionalBinaryCheck ("op_BitwiseAnd", left, right, method);

			return MakeBoolBinary (ExpressionType.AndAlso, left, right, true, method);
		}

		static MethodInfo ConditionalBinaryCheck (string oper, Expression left, Expression right, MethodInfo method)
		{
			method = BinaryCoreCheck (oper, left, right, method);

			if (method == null) {
				if (left.Type.GetNotNullableType () != typeof (bool))
					throw new InvalidOperationException ("Only booleans are allowed");
			} else {
				var type = left.Type.GetNotNullableType ();

				// The method should have identical parameter and return types.
				if (left.Type != right.Type || method.ReturnType != type)
					throw new ArgumentException ("left, right and return type must match");

				var optrue = GetTrueOperator (type);
				var opfalse = GetFalseOperator (type);

				if (optrue == null || opfalse == null)
					throw new ArgumentException ("Operators true and false are required but not defined");
			}

			return method;
		}

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

		public static BinaryExpression OrElse (Expression left, Expression right, MethodInfo method)
		{
			method = ConditionalBinaryCheck ("op_BitwiseOr", left, right, method);

			return MakeBoolBinary (ExpressionType.OrElse, left, right, true, method);
		}

		//
		// Comparison
		//
		public static BinaryExpression Equal (Expression left, Expression right)
		{
			return Equal (left, right, false, null);
		}

		public static BinaryExpression Equal (Expression left, Expression right, bool liftToNull, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_Equality", left, right, method);

			return MakeBoolBinary (ExpressionType.Equal, left, right, liftToNull, method);
		}

		public static BinaryExpression NotEqual (Expression left, Expression right)
		{
			return NotEqual (left, right, false, null);
		}


		public static BinaryExpression NotEqual (Expression left, Expression right, bool liftToNull, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_Inequality", left, right, method);

			return MakeBoolBinary (ExpressionType.NotEqual, left, right, liftToNull, method);
		}

		public static BinaryExpression GreaterThan (Expression left, Expression right)
		{
			return GreaterThan (left, right, false, null);
		}

		public static BinaryExpression GreaterThan (Expression left, Expression right, bool liftToNull, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_GreaterThan", left, right, method);

			return MakeBoolBinary (ExpressionType.GreaterThan, left, right, liftToNull, method);
		}

		public static BinaryExpression GreaterThanOrEqual (Expression left, Expression right)
		{
			return GreaterThanOrEqual (left, right, false, null);
		}


		public static BinaryExpression GreaterThanOrEqual (Expression left, Expression right, bool liftToNull, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_GreaterThanOrEqual", left, right, method);

			return MakeBoolBinary (ExpressionType.GreaterThanOrEqual, left, right, liftToNull, method);
		}

		public static BinaryExpression LessThan (Expression left, Expression right)
		{
			return LessThan (left, right, false, null);
		}

		public static BinaryExpression LessThan (Expression left, Expression right, bool liftToNull, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_LessThan", left, right, method);

			return MakeBoolBinary (ExpressionType.LessThan, left, right, liftToNull, method);
		}

		public static BinaryExpression LessThanOrEqual (Expression left, Expression right)
		{
			return LessThanOrEqual (left, right, false, null);
		}

		public static BinaryExpression LessThanOrEqual (Expression left, Expression right, bool liftToNull, MethodInfo method)
		{
			method = BinaryCoreCheck ("op_LessThanOrEqual", left, right, method);

			return MakeBoolBinary (ExpressionType.LessThanOrEqual, left, right, liftToNull, method);
		}

		//
		// Miscelaneous
		//

		static void CheckArray (Expression array)
		{
			if (array == null)
				throw new ArgumentNullException ("array");
			if (!array.Type.IsArray)
				throw new ArgumentException ("The array argument must be of type array");
		}

		public static BinaryExpression ArrayIndex (Expression array, Expression index)
		{
			CheckArray (array);

			if (index == null)
				throw new ArgumentNullException ("index");
			if (array.Type.GetArrayRank () != 1)
				throw new ArgumentException ("The array argument must be a single dimensional array");
			if (index.Type != typeof (int))
				throw new ArgumentException ("The index must be of type int");

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

		public static BinaryExpression Coalesce (Expression left, Expression right)
		{
			return Coalesce (left, right, null);
		}

		static BinaryExpression MakeCoalesce (Expression left, Expression right)
		{
			Type result = null;

			if (left.Type.IsNullable ()) {
				Type lbase = left.Type.GetNotNullableType ();

				if (!right.Type.IsNullable () && right.Type.IsAssignableTo (lbase))
					result = lbase;
			}

			if (result == null && right.Type.IsAssignableTo (left.Type))
				result = left.Type;

			if (result == null) {
				if (left.Type.IsNullable () && left.Type.GetNotNullableType ().IsAssignableTo (right.Type))
					result = right.Type;
			}

			if (result == null)
				throw new ArgumentException ("Incompatible argument types");

			return new BinaryExpression (ExpressionType.Coalesce, result, left, right, false, false, null, null);
		}

		static BinaryExpression MakeConvertedCoalesce (Expression left, Expression right, LambdaExpression conversion)
		{
			var invoke = conversion.Type.GetInvokeMethod ();

			CheckNotVoid (invoke.ReturnType);

			if (invoke.ReturnType != right.Type)
				throw new InvalidOperationException ("Conversion return type doesn't march right type");

			var parameters = invoke.GetParameters ();

			if (parameters.Length != 1)
				throw new ArgumentException ("Conversion has wrong number of parameters");

			if (!IsAssignableToParameterType (left.Type, parameters [0]))
				throw new InvalidOperationException ("Conversion argument doesn't marcht left type");

			return new BinaryExpression (ExpressionType.Coalesce, right.Type, left, right, false, false, null, conversion);
		}

		public static BinaryExpression Coalesce (Expression left, Expression right, LambdaExpression conversion)
		{
			if (left == null)
				throw new ArgumentNullException ("left");
			if (right == null)
				throw new ArgumentNullException ("right");

			//
			// First arg must ne nullable (either Nullable<T> or a reference type
			//
			if (left.Type.IsValueType && !left.Type.IsNullable ())
				throw new InvalidOperationException ("Left expression can never be null");

			if (conversion != null)
				return MakeConvertedCoalesce (left, right, conversion);

			return MakeCoalesce (left, right);
		}

		//
		// MakeBinary constructors
		//
		public static BinaryExpression MakeBinary (ExpressionType binaryType, Expression left, Expression right)
		{
			return MakeBinary (binaryType, left, right, false, null);
		}

		public static BinaryExpression MakeBinary (ExpressionType binaryType, Expression left, Expression right, bool liftToNull, MethodInfo method)
		{
			return MakeBinary (binaryType, left, right, liftToNull, method, null);
		}

		public static BinaryExpression MakeBinary (ExpressionType binaryType, Expression left, Expression right, bool liftToNull, MethodInfo method, LambdaExpression conversion)
		{
			switch (binaryType) {
			case ExpressionType.Add:
				return Add (left, right, method);
			case ExpressionType.AddChecked:
				return AddChecked (left, right, method);
			case ExpressionType.AndAlso:
				return AndAlso (left, right);
			case ExpressionType.Coalesce:
				return Coalesce (left, right, conversion);
			case ExpressionType.Divide:
				return Divide (left, right, method);
			case ExpressionType.Equal:
				return Equal (left, right, liftToNull, method);
			case ExpressionType.ExclusiveOr:
				return ExclusiveOr (left, right, method);
			case ExpressionType.GreaterThan:
				return GreaterThan (left, right, liftToNull, method);
			case ExpressionType.GreaterThanOrEqual:
				return GreaterThanOrEqual (left, right, liftToNull, method);
			case ExpressionType.LeftShift:
				return LeftShift (left, right, method);
			case ExpressionType.LessThan:
				return LessThan (left, right, liftToNull, method);
			case ExpressionType.LessThanOrEqual:
				return LessThanOrEqual (left, right, liftToNull, method);
			case ExpressionType.Modulo:
				return Modulo (left, right, method);
			case ExpressionType.Multiply:
				return Multiply (left, right, method);
			case ExpressionType.MultiplyChecked:
				return MultiplyChecked (left, right, method);
			case ExpressionType.NotEqual:
				return NotEqual (left, right, liftToNull, method);
			case ExpressionType.OrElse:
				return OrElse (left, right);
			case ExpressionType.Power:
				return Power (left, right, method);
			case ExpressionType.RightShift:
				return RightShift (left, right, method);
			case ExpressionType.Subtract:
				return Subtract (left, right, method);
			case ExpressionType.SubtractChecked:
				return SubtractChecked (left, right, method);
			case ExpressionType.And:
				return And (left, right, method);
			case ExpressionType.Or:
				return Or (left, right, method);
			}

			throw new ArgumentException ("MakeBinary expect a binary node type");
		}

		#endregion

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

		public static MethodCallExpression ArrayIndex (Expression array, IEnumerable<Expression> indexes)
		{
			CheckArray (array);

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

			var args = indexes.ToReadOnlyCollection ();
			if (array.Type.GetArrayRank () != args.Count)
				throw new ArgumentException ("The number of arguments doesn't match the rank of the array");

			foreach (var arg in args)
				if (arg.Type != typeof (int))
					throw new ArgumentException ("The index must be of type int");

			return Call (array, array.Type.GetMethod ("Get", PublicInstance), args);
		}

		public static UnaryExpression ArrayLength (Expression array)
		{
			if (array == null)
				throw new ArgumentNullException ("array");
			if (!array.Type.IsArray)
				throw new ArgumentException ("The type of the expression must me Array");
			if (array.Type.GetArrayRank () != 1)
				throw new ArgumentException ("The array must be a single dimensional array");

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

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

			Type type = null;

			var prop = member as PropertyInfo;
			if (prop != null && prop.GetSetMethod (true) != null)
				type = prop.PropertyType;

			var field = member as FieldInfo;
			if (field != null)
				type = field.FieldType;

			if (type == null)
				throw new ArgumentException ("member");

			if (!expression.Type.IsAssignableTo (type))
				throw new ArgumentException ("member");

			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");

			CheckNonGenericMethod (propertyAccessor);

			var prop = GetAssociatedProperty (propertyAccessor);
			if (prop == null)
				throw new ArgumentException ("propertyAccessor");

			var setter = prop.GetSetMethod (true);
			if (setter == null)
				throw new ArgumentException ("setter");

			if (!expression.Type.IsAssignableTo (prop.PropertyType))
				throw new ArgumentException ("member");

			return new MemberAssignment (prop, expression);
		}

		public static MethodCallExpression Call (Expression instance, MethodInfo method)
		{
			return Call (instance, method, null as IEnumerable<Expression>);
		}

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

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

		public static MethodCallExpression Call (Expression instance, MethodInfo method, IEnumerable<Expression> arguments)
		{
			if (method == null)
				throw new ArgumentNullException ("method");
			if (instance == null && !method.IsStatic)
				throw new ArgumentNullException ("instance");
			if (method.IsStatic && instance != null)
				throw new ArgumentException ("instance");
			if (!method.IsStatic && !instance.Type.IsAssignableTo (method.DeclaringType))
				throw new ArgumentException ("Type is not assignable to the declaring type of the method");

			var args = CheckMethodArguments (method, arguments);

			return new MethodCallExpression (instance, method, args);
		}

		static Type [] CollectTypes (IEnumerable<Expression> expressions)
		{
			return (from arg in expressions select arg.Type).ToArray ();
		}

		static MethodInfo TryMakeGeneric (MethodInfo method, Type [] args)
		{
			if (method == null)
				return null;

			if (!method.IsGenericMethod && (args == null || args.Length == 0))
				return method;

			if (args.Length == method.GetGenericArguments ().Length)
				return method.MakeGenericMethod (args);

			return null;
		}

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

			var method = TryGetMethod (instance.Type, methodName, AllInstance,
				CollectTypes (arguments), typeArguments);

			var args = CheckMethodArguments (method, arguments);

			return new MethodCallExpression (instance, method, args);
		}

		static bool MethodMatch (MethodInfo method, string name, Type [] parameterTypes, Type [] argumentTypes)
		{
			if (method.Name != name)
				return false;

			var parameters = method.GetParameters ();

			if (parameters.Length != parameterTypes.Length)
				return false;

			if (method.IsGenericMethod && method.IsGenericMethodDefinition) {
				var closed = TryMakeGeneric (method, argumentTypes);
				if (closed == null)
					return false;

				return MethodMatch (closed, name, parameterTypes, argumentTypes);
			} else if (!method.IsGenericMethod && (argumentTypes != null && argumentTypes.Length > 0))
				return false;

			for (int i = 0; i < parameters.Length; i++) {
				var type = parameterTypes [i];
				var parameter = parameters [i];
				if (!IsAssignableToParameterType (type, parameter)
					&& !IsExpressionOfParameter (type, parameter.ParameterType))
					return false;
			}

			return true;
		}

		static bool IsExpressionOfParameter (Type type, Type ptype)
		{
			return ptype.IsGenericInstanceOf (typeof (Expression<>)) && ptype.GetFirstGenericArgument () == type;
		}

		static MethodInfo TryGetMethod (Type type, string methodName, BindingFlags flags, Type [] parameterTypes, Type [] argumentTypes)
		{
			var methods = from meth in type.GetMethods (flags)
						  where MethodMatch (meth, methodName, parameterTypes, argumentTypes)
						  select meth;

			if (methods.Count () > 1)
				throw new InvalidOperationException ("Too many method candidates");

			var method = TryMakeGeneric (methods.FirstOrDefault (), argumentTypes);
			if (method != null)
				return method;

			throw new InvalidOperationException ("No such method");
		}

		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");

			var method = TryGetMethod (type, methodName, AllStatic,
				CollectTypes (arguments), typeArguments);

			var args = CheckMethodArguments (method, arguments);

			return new MethodCallExpression (method, args);
		}

		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 ("Test expression should be of type bool");
			if (ifTrue.Type != ifFalse.Type)
				throw new ArgumentException ("The ifTrue and ifFalse type do not match");

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

		public static ConstantExpression Constant (object value)
		{
			if (value == null)
				return new ConstantExpression (null, typeof (object));

			return Constant (value, value.GetType ());
		}

		public static ConstantExpression Constant (object value, Type type)
		{
			if (type == null)
				throw new ArgumentNullException ("type");

			//
			// value must be compatible with type, no conversions
			// are allowed
			//
			if (value == null){
				if (type.IsValueType && !type.IsNullable ())
					throw new ArgumentException ();
			} else {
				if (!(type.IsValueType && type.IsNullable ()) && !value.GetType ().IsAssignableTo (type))
					throw new ArgumentException ();

			}

			return new ConstantExpression (value, type);
		}

		static bool IsConvertiblePrimitive (Type type)
		{
			var t = type.GetNotNullableType ();

			if (t == typeof (bool))
				return false;

			if (t.IsEnum)
				return true;

			return t.IsPrimitive;
		}

		internal static bool IsPrimitiveConversion (Type type, Type target)
		{
			if (type == target)
				return true;

			if (type.IsNullable () && target == type.GetNotNullableType ())
				return true;

			if (target.IsNullable () && type == target.GetNotNullableType ())
				return true;

			if (IsConvertiblePrimitive (type) && IsConvertiblePrimitive (target))
				return true;

			return false;
		}

		internal static bool IsReferenceConversion (Type type, Type target)
		{
			if (type == target)
				return true;

			if (type == typeof (object) || target == typeof (object))
				return true;

			if (type.IsInterface || target.IsInterface)
				return true;

			if (type.IsValueType || target.IsValueType)
				return false;

			if (type.IsAssignableTo (target) || target.IsAssignableTo (type))
				return true;

			return false;
		}

		public static UnaryExpression Convert (Expression expression, Type type)
		{
			return Convert (expression, type, null);
		}

		static MethodInfo GetUserConversionMethod (Type type, Type target)
		{
			var method = GetUnaryOperator ("op_Explicit", type, type, target);
			if (method == null)
				method = GetUnaryOperator ("op_Implicit", type, type, target);
			if (method == null)
				method = GetUnaryOperator ("op_Explicit", target, type, target);
			if (method == null)
				method = GetUnaryOperator ("op_Implicit", target, type, target);
			if (method == null)
				throw new InvalidOperationException ();

			return method;
		}

		public static UnaryExpression Convert (Expression expression, Type type, MethodInfo method)
		{
			if (expression == null)
				throw new ArgumentNullException ("expression");
			if (type == null)
				throw new ArgumentNullException ("type");

			var et = expression.Type;

			if (method != null)
				CheckUnaryMethod (method, et);
			else if (!IsPrimitiveConversion (et, type) && !IsReferenceConversion (et, type))
				method = GetUserConversionMethod (et, type);

			return new UnaryExpression (ExpressionType.Convert,
				expression, type, method,
				IsConvertNodeLifted (method, expression, type));
		}

		static bool IsConvertNodeLifted (MethodInfo method, Expression operand, Type target)
		{
			if (method == null)
				return operand.Type.IsNullable () || target.IsNullable ();

			if (operand.Type.IsNullable () && !ParameterMatch (method, operand.Type))
				return true;

			if (target.IsNullable () && !ReturnTypeMatch (method, target))
				return true;

			return false;
		}

		static bool ParameterMatch (MethodInfo method, Type type)
		{
			return method.GetParameters () [0].ParameterType == type;
		}

		static bool ReturnTypeMatch (MethodInfo method, Type type)
		{
			return method.ReturnType == type;
		}

		public static UnaryExpression ConvertChecked (Expression expression, Type type)
		{
			return ConvertChecked (expression, type, null);
		}

		public static UnaryExpression ConvertChecked (Expression expression, Type type, MethodInfo method)
		{
			if (expression == null)
				throw new ArgumentNullException ("expression");
			if (type == null)
				throw new ArgumentNullException ("type");

			var et = expression.Type;

			if (method != null)
				CheckUnaryMethod (method, et);
			else if (IsReferenceConversion (et, type))
				return Convert (expression, type, method);
			else if (!IsPrimitiveConversion (et, type))
				method = GetUserConversionMethod (et, type);

			return new UnaryExpression (ExpressionType.ConvertChecked,
				expression, type, method,
				IsConvertNodeLifted (method, expression, type));
		}

		public static ElementInit ElementInit (MethodInfo addMethod, params Expression [] arguments)
		{
			return ElementInit (addMethod, arguments as IEnumerable<Expression>);
		}

		public static ElementInit ElementInit (MethodInfo addMethod, IEnumerable<Expression> arguments)
		{
			if (addMethod == null)
				throw new ArgumentNullException ("addMethod");
			if (arguments == null)
				throw new ArgumentNullException ("arguments");
			if (addMethod.Name.ToLower (CultureInfo.InvariantCulture) != "add")
				throw new ArgumentException ("addMethod");
			if (addMethod.IsStatic)
				throw new ArgumentException ("addMethod must be an instance method", "addMethod");

			var args = CheckMethodArguments (addMethod, arguments);

			return new ElementInit (addMethod, args);
		}

		public static MemberExpression Field (Expression expression, FieldInfo field)
		{
			if (field == null)
				throw new ArgumentNullException ("field");
			if (!field.IsStatic) {
				if (expression == null)
					throw new ArgumentNullException ("expression");
				if (!expression.Type.IsAssignableTo (field.DeclaringType))
					throw new ArgumentException ("field");
			} else if (expression != null)
				throw new ArgumentException ("expression");

			return new MemberExpression (expression, field, field.FieldType);
		}

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

			var field = expression.Type.GetField (fieldName, AllInstance);
			if (field == null)
				throw new ArgumentException (string.Format ("No field named {0} on {1}", fieldName, expression.Type));

			return new MemberExpression (expression, field, field.FieldType);
		}

		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);
		}

		public static InvocationExpression Invoke (Expression expression, params Expression [] arguments)
		{
			return Invoke (expression, arguments as IEnumerable<Expression>);
		}

		static Type GetInvokableType (Type t)
		{
			if (t.IsAssignableTo (typeof (Delegate)))
				return t;

			return GetGenericType (t, typeof (Expression<>));
		}

		static Type GetGenericType (Type t, Type def)
		{
			if (t == null)
				return null;

			if (t.IsGenericType && t.GetGenericTypeDefinition () == def)
				return t;

			return GetGenericType (t.BaseType, def);
		}

		public static InvocationExpression Invoke (Expression expression, IEnumerable<Expression> arguments)
		{
			if (expression == null)
				throw new ArgumentNullException ("expression");

			var type = GetInvokableType (expression.Type);
			if (type == null)
				throw new ArgumentException ("The type of the expression is not invokable");

			var args = arguments.ToReadOnlyCollection ();
			CheckForNull (args, "arguments");

			var invoke = type.GetInvokeMethod ();
			if (invoke == null)
				throw new ArgumentException ("expression");

			if (invoke.GetParameters ().Length != args.Count)
				throw new InvalidOperationException ("Arguments count doesn't match parameters length");

			args = CheckMethodArguments (invoke, args);

			return new InvocationExpression (expression, invoke.ReturnType, args);
		}

		static bool CanAssign (Type target, Type source)
		{
			// This catches object and value type mixage, type compatibility is handled later
			if (target.IsValueType ^ source.IsValueType)
				return false;

			return source.IsAssignableTo (target);
		}

		static Expression CheckLambda (Type delegateType, Expression body, ReadOnlyCollection<ParameterExpression> parameters)
		{
			if (!delegateType.IsSubclassOf (typeof (System.Delegate)))
				throw new ArgumentException ("delegateType");

			var invoke = delegateType.GetInvokeMethod ();
			if (invoke == null)
				throw new ArgumentException ("delegate must contain an Invoke method", "delegateType");

			var invoke_parameters = invoke.GetParameters ();
			if (invoke_parameters.Length != parameters.Count)
				throw new ArgumentException (string.Format ("Different number of arguments in delegate {0}", delegateType), "delegateType");

			for (int i = 0; i < invoke_parameters.Length; i++) {
				var parameter = parameters [i];
				if (parameter == null)
					throw new ArgumentNullException ("parameters");

				if (!CanAssign (parameter.Type, invoke_parameters [i].ParameterType))
					throw new ArgumentException (String.Format ("Can not assign a {0} to a {1}", invoke_parameters [i].ParameterType, parameter.Type));
			}

			if (invoke.ReturnType != typeof (void)) {
				if (!CanAssign (invoke.ReturnType, body.Type)) {
					if (invoke.ReturnType.IsExpression ())
						return Expression.Quote (body);

					throw new ArgumentException (String.Format ("body type {0} can not be assigned to {1}", body.Type, invoke.ReturnType));
				}
			}
			return body;
		}

		public static Expression<TDelegate> Lambda<TDelegate> (Expression body, params ParameterExpression [] parameters)
		{
			return Lambda<TDelegate> (body, parameters as IEnumerable<ParameterExpression>);
		}

		public static Expression<TDelegate> Lambda<TDelegate> (Expression body, IEnumerable<ParameterExpression> parameters)
		{
			if (body == null)
				throw new ArgumentNullException ("body");

			var ps = parameters.ToReadOnlyCollection ();

			body = CheckLambda (typeof (TDelegate), body, ps);

			return new Expression<TDelegate> (body, ps);
		}

		public static LambdaExpression Lambda (Expression body, params ParameterExpression [] parameters)
		{
			if (body == null)
				throw new ArgumentNullException ("body");
			if (parameters.Length > 4)
				throw new ArgumentException ("Too many parameters");

			return Lambda (GetDelegateType (body.Type, parameters), body, parameters);
		}

		static Type GetDelegateType (Type return_type, ParameterExpression [] parameters)
		{
			if (parameters == null)
				parameters = new ParameterExpression [0];

			if (return_type == typeof (void))
				return GetActionType (parameters.Select (p => p.Type).ToArray ());

			var types = new Type [parameters.Length + 1];
			for (int i = 0; i < types.Length - 1; i++)
				types [i] = parameters [i].Type;

			types [types.Length - 1] = return_type;
			return GetFuncType (types);
		}

		public static LambdaExpression Lambda (Type delegateType, Expression body, params ParameterExpression [] parameters)
		{
			return Lambda (delegateType, body, parameters as IEnumerable<ParameterExpression>);
		}

		static LambdaExpression CreateExpressionOf (Type type, Expression body, ReadOnlyCollection<ParameterExpression> parameters)
		{
			return (LambdaExpression) typeof (Expression<>).MakeGenericType (type).GetConstructor (
				NonPublicInstance, null, new [] { typeof (Expression), typeof (ReadOnlyCollection<ParameterExpression>) }, null).Invoke (new object [] { body, parameters } );
		}

		public static LambdaExpression Lambda (Type delegateType, Expression body, IEnumerable<ParameterExpression> parameters)
		{
			if (delegateType == null)
				throw new ArgumentNullException ("delegateType");
			if (body == null)
				throw new ArgumentNullException ("body");

			var ps = parameters.ToReadOnlyCollection ();

			body = CheckLambda (delegateType, body, ps);

			return CreateExpressionOf (delegateType, body, ps);
		}

		public static MemberListBinding ListBind (MemberInfo member, params ElementInit [] initializers)
		{
			return ListBind (member, initializers as IEnumerable<ElementInit>);
		}

		static void CheckIsAssignableToIEnumerable (Type t)
		{
			if (!t.IsAssignableTo (typeof (IEnumerable)))
				throw new ArgumentException (string.Format ("Type {0} doesn't implemen IEnumerable", t));
		}

		public static MemberListBinding ListBind (MemberInfo member, IEnumerable<ElementInit> initializers)
		{
			if (member == null)
				throw new ArgumentNullException ("member");
			if (initializers == null)
				throw new ArgumentNullException ("initializers");

			var inits = initializers.ToReadOnlyCollection ();
			CheckForNull (inits, "initializers");

			member.OnFieldOrProperty (
				field => CheckIsAssignableToIEnumerable (field.FieldType),
				prop => CheckIsAssignableToIEnumerable (prop.PropertyType));

			return new MemberListBinding (member, inits);
		}

		public static MemberListBinding ListBind (MethodInfo propertyAccessor, params ElementInit [] initializers)
		{
			return ListBind (propertyAccessor, initializers as IEnumerable<ElementInit>);
		}

		static void CheckForNull<T> (ReadOnlyCollection<T> collection, string name) where T : class
		{
			foreach (var t in collection)
				if (t == null)
					throw new ArgumentNullException (name);
		}

		public static MemberListBinding ListBind (MethodInfo propertyAccessor, IEnumerable<ElementInit> initializers)
		{
			if (propertyAccessor == null)
				throw new ArgumentNullException ("propertyAccessor");
			if (initializers == null)
				throw new ArgumentNullException ("initializers");

			var inits = initializers.ToReadOnlyCollection ();
			CheckForNull (inits, "initializers");

			var prop = GetAssociatedProperty (propertyAccessor);
			if (prop == null)
				throw new ArgumentException ("propertyAccessor");

			CheckIsAssignableToIEnumerable (prop.PropertyType);

			return new MemberListBinding (prop, inits);
		}

		public static ListInitExpression ListInit (NewExpression newExpression, params ElementInit [] initializers)
		{
			return ListInit (newExpression, initializers as IEnumerable<ElementInit>);
		}

		public static ListInitExpression ListInit (NewExpression newExpression, IEnumerable<ElementInit> initializers)
		{
			var inits = CheckListInit (newExpression, initializers);

			return new ListInitExpression (newExpression, inits);
		}

		public static ListInitExpression ListInit (NewExpression newExpression, params Expression [] initializers)
		{
			return ListInit (newExpression, initializers as IEnumerable<Expression>);
		}

		public static ListInitExpression ListInit (NewExpression newExpression, IEnumerable<Expression> initializers)
		{
			var inits = CheckListInit (newExpression, initializers);

			var add_method = GetAddMethod (newExpression.Type, inits [0].Type);
			if (add_method == null)
				throw new InvalidOperationException ("No suitable add method found");

			return new ListInitExpression (newExpression, CreateInitializers (add_method, inits));
		}

		static ReadOnlyCollection<ElementInit> CreateInitializers (MethodInfo add_method, ReadOnlyCollection<Expression> initializers)
		{
			return (from init in initializers select Expression.ElementInit (add_method, init)).ToReadOnlyCollection ();
		}

		static MethodInfo GetAddMethod (Type type, Type arg)
		{
			return type.GetMethod ("Add", PublicInstance | BindingFlags.IgnoreCase, null, new [] { arg }, null);
		}

		public static ListInitExpression ListInit (NewExpression newExpression, MethodInfo addMethod, params Expression [] initializers)
		{
			return ListInit (newExpression, addMethod, initializers as IEnumerable<Expression>);
		}

		static ReadOnlyCollection<T> CheckListInit<T> (NewExpression newExpression, IEnumerable<T> initializers) where T : class
		{
			if (newExpression == null)
				throw new ArgumentNullException ("newExpression");
			if (initializers == null)
				throw new ArgumentNullException ("initializers");
			if (!newExpression.Type.IsAssignableTo (typeof (IEnumerable)))
				throw new InvalidOperationException ("The type of the new expression does not implement IEnumerable");

			var inits = initializers.ToReadOnlyCollection ();
			if (inits.Count == 0)
				throw new ArgumentException ("Empty initializers");

			CheckForNull (inits, "initializers");

			return inits;
		}

		public static ListInitExpression ListInit (NewExpression newExpression, MethodInfo addMethod, IEnumerable<Expression> initializers)
		{
			var inits = CheckListInit (newExpression, initializers);

			if (addMethod != null) {
				if (addMethod.Name.ToLower (CultureInfo.InvariantCulture) != "add")
					throw new ArgumentException ("addMethod");

				var parameters = addMethod.GetParameters ();
				if (parameters.Length != 1)
					throw new ArgumentException ("addMethod");

				foreach (var expression in inits)
					if (!IsAssignableToParameterType (expression.Type, parameters [0]))
						throw new InvalidOperationException ("Initializer not assignable to the add method parameter type");
			}

			if (addMethod == null)
				addMethod = GetAddMethod (newExpression.Type, inits [0].Type);

			if (addMethod == null)
				throw new InvalidOperationException ("No suitable add method found");

			return new ListInitExpression (newExpression, CreateInitializers (addMethod, inits));
		}

		public static MemberExpression MakeMemberAccess (Expression expression, MemberInfo member)
		{
			if (expression == null)
				throw new ArgumentNullException ("expression");
			if (member == null)
				throw new ArgumentNullException ("member");

			var field = member as FieldInfo;
			if (field != null)
				return Field (expression, field);

			var property = member as PropertyInfo;
			if (property != null)
				return Property (expression, property);

			throw new ArgumentException ("Member should either be a field or a property");
		}

		public static UnaryExpression MakeUnary (ExpressionType unaryType, Expression operand, Type type)
		{
			return MakeUnary (unaryType, operand, type, null);
		}

		public static UnaryExpression MakeUnary (ExpressionType unaryType, Expression operand, Type type, MethodInfo method)
		{
			switch (unaryType) {
			case ExpressionType.ArrayLength:
				return ArrayLength (operand);
			case ExpressionType.Convert:
				return Convert (operand, type, method);
			case ExpressionType.ConvertChecked:
				return ConvertChecked (operand, type, method);
			case ExpressionType.Negate:
				return Negate (operand, method);
			case ExpressionType.NegateChecked:
				return NegateChecked (operand, method);
			case ExpressionType.Not:
				return Not (operand, method);
			case ExpressionType.Quote:
				return Quote (operand);
			case ExpressionType.TypeAs:
				return TypeAs (operand, type);
			case ExpressionType.UnaryPlus:
				return UnaryPlus (operand, method);
			}

			throw new ArgumentException ("MakeUnary expect an unary operator");
		}

		public static MemberMemberBinding MemberBind (MemberInfo member, params MemberBinding [] bindings)
		{
			return MemberBind (member, bindings as IEnumerable<MemberBinding>);
		}

		public static MemberMemberBinding MemberBind (MemberInfo member, IEnumerable<MemberBinding> bindings)
		{
			if (member == null)
				throw new ArgumentNullException ("member");

			var type = member.OnFieldOrProperty (
				field => field.FieldType,
				prop => prop.PropertyType);

			return new MemberMemberBinding (member, CheckMemberBindings (type, bindings));
		}

		public static MemberMemberBinding MemberBind (MethodInfo propertyAccessor, params MemberBinding [] bindings)
		{
			return MemberBind (propertyAccessor, bindings as IEnumerable<MemberBinding>);
		}

		public static MemberMemberBinding MemberBind (MethodInfo propertyAccessor, IEnumerable<MemberBinding> bindings)
		{
			if (propertyAccessor == null)
				throw new ArgumentNullException ("propertyAccessor");

			var bds = bindings.ToReadOnlyCollection ();
			CheckForNull (bds, "bindings");

			var prop = GetAssociatedProperty (propertyAccessor);
			if (prop == null)
				throw new ArgumentException ("propertyAccessor");

			return new MemberMemberBinding (prop, CheckMemberBindings (prop.PropertyType, bindings));
		}

		static ReadOnlyCollection<MemberBinding> CheckMemberBindings (Type type, IEnumerable<MemberBinding> bindings)
		{
			if (bindings == null)
				throw new ArgumentNullException ("bindings");

			var bds = bindings.ToReadOnlyCollection ();
			CheckForNull (bds, "bindings");

			foreach (var binding in bds)
				if (!type.IsAssignableTo (binding.Member.DeclaringType))
					throw new ArgumentException ("Type not assignable to member type");

			return bds;
		}

		public static MemberInitExpression MemberInit (NewExpression newExpression, params MemberBinding [] bindings)
		{
			return MemberInit (newExpression, bindings as IEnumerable<MemberBinding>);
		}

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

			return new MemberInitExpression (newExpression, CheckMemberBindings (newExpression.Type, bindings));
		}

		public static UnaryExpression Negate (Expression expression)
		{
			return Negate (expression, null);
		}

		public static UnaryExpression Negate (Expression expression, MethodInfo method)
		{
			method = UnaryCoreCheck ("op_UnaryNegation", expression, method, type => IsSignedNumber (type));

			return MakeSimpleUnary (ExpressionType.Negate, expression, method);
		}

		public static UnaryExpression NegateChecked (Expression expression)
		{
			return NegateChecked (expression, null);
		}

		public static UnaryExpression NegateChecked (Expression expression, MethodInfo method)
		{
			method = UnaryCoreCheck ("op_UnaryNegation", expression, method, type => IsSignedNumber (type));

			return MakeSimpleUnary (ExpressionType.NegateChecked, expression, method);
		}

		public static NewExpression New (ConstructorInfo constructor)
		{
			if (constructor == null)
				throw new ArgumentNullException ("constructor");

			if (constructor.GetParameters ().Length > 0)
				throw new ArgumentException ("Constructor must be parameter less");

			return new NewExpression (constructor, (null as IEnumerable<Expression>).ToReadOnlyCollection (), null);
		}

		public static NewExpression New (Type type)
		{
			if (type == null)
				throw new ArgumentNullException ("type");

			CheckNotVoid (type);

			var args = (null as IEnumerable<Expression>).ToReadOnlyCollection ();

			if (type.IsValueType)
				return new NewExpression (type, args);

			var ctor = type.GetConstructor (Type.EmptyTypes);
			if (ctor == null)
				throw new ArgumentException ("Type doesn't have a parameter less constructor");

			return new NewExpression (ctor, args, null);
		}

		public static NewExpression New (ConstructorInfo constructor, params Expression [] arguments)
		{
			return New (constructor, arguments as IEnumerable<Expression>);
		}

		public static NewExpression New (ConstructorInfo constructor, IEnumerable<Expression> arguments)
		{
			if (constructor == null)
				throw new ArgumentNullException ("constructor");

			var args = CheckMethodArguments (constructor, arguments);

			return new NewExpression (constructor, args, null);
		}

		static IList<Expression> CreateArgumentList (IEnumerable<Expression> arguments)
		{
			if (arguments == null)
				return arguments.ToReadOnlyCollection ();

			return arguments.ToList ();
		}

		static void CheckNonGenericMethod (MethodBase method)
		{
			if (method.IsGenericMethodDefinition || method.ContainsGenericParameters)
				throw new ArgumentException ("Can not used open generic methods");
		}

		static ReadOnlyCollection<Expression> CheckMethodArguments (MethodBase method, IEnumerable<Expression> args)
		{
			CheckNonGenericMethod (method);

			var arguments = CreateArgumentList (args);
			var parameters = method.GetParameters ();

			if (arguments.Count != parameters.Length)
				throw new ArgumentException ("The number of arguments doesn't match the number of parameters");

			for (int i = 0; i < parameters.Length; i++) {
				if (arguments [i] == null)
					throw new ArgumentNullException ("arguments");

				if (!IsAssignableToParameterType (arguments [i].Type, parameters [i])) {
					if (!parameters [i].ParameterType.IsExpression ())
						throw new ArgumentException ("arguments");

					arguments [i] = Expression.Quote (arguments [i]);
				}
			}

			return arguments.ToReadOnlyCollection ();
		}

		public static NewExpression New (ConstructorInfo constructor, IEnumerable<Expression> arguments, params MemberInfo [] members)
		{
			return New (constructor, arguments, members as IEnumerable<MemberInfo>);
		}

		public static NewExpression New (ConstructorInfo constructor, IEnumerable<Expression> arguments, IEnumerable<MemberInfo> members)
		{
			if (constructor == null)
				throw new ArgumentNullException ("constructor");

			var args = arguments.ToReadOnlyCollection ();
			var mmbs = members.ToReadOnlyCollection ();

			CheckForNull (args, "arguments");
			CheckForNull (mmbs, "members");

			args = CheckMethodArguments (constructor, arguments);

			if (args.Count != mmbs.Count)
				throw new ArgumentException ("Arguments count does not match members count");

			for (int i = 0; i < mmbs.Count; i++) {
				var member = mmbs [i];
				Type type = null;
				switch (member.MemberType) {
				case MemberTypes.Field:
					type = (member as FieldInfo).FieldType;
					break;
				case MemberTypes.Method:
					type = (member as MethodInfo).ReturnType;
					break;
				case MemberTypes.Property:
					var prop = member as PropertyInfo;
					if (prop.GetGetMethod (true) == null)
						throw new ArgumentException ("Property must have a getter");

					type = (member as PropertyInfo).PropertyType;
					break;
				default:
					throw new ArgumentException ("Member type not allowed");
				}

				if (!args [i].Type.IsAssignableTo (type))
					throw new ArgumentException ("Argument type not assignable to member type");
			}

			return new NewExpression (constructor, args, mmbs);
		}

		public static NewArrayExpression NewArrayBounds (Type type, params Expression [] bounds)
		{
			return NewArrayBounds (type, bounds as IEnumerable<Expression>);
		}

		public static NewArrayExpression NewArrayBounds (Type type, IEnumerable<Expression> bounds)
		{
			if (type == null)
				throw new ArgumentNullException ("type");
			if (bounds == null)
				throw new ArgumentNullException ("bounds");

			CheckNotVoid (type);

			var array_bounds = bounds.ToReadOnlyCollection ();
			foreach (var expression in array_bounds)
				if (!IsInt (expression.Type))
					throw new ArgumentException ("The bounds collection can only contain expression of integers types");

			return new NewArrayExpression (ExpressionType.NewArrayBounds, type.MakeArrayType (array_bounds.Count), array_bounds);
		}

		public static NewArrayExpression NewArrayInit (Type type, params Expression [] initializers)
		{
			return NewArrayInit (type, initializers as IEnumerable<Expression>);
		}

		public static NewArrayExpression NewArrayInit (Type type, IEnumerable<Expression> initializers)
		{
			if (type == null)
				throw new ArgumentNullException ("type");
			if (initializers == null)
				throw new ArgumentNullException ("initializers");

			CheckNotVoid (type);

			var inits = initializers.ToReadOnlyCollection ();

			foreach (var expression in inits) {
				if (expression == null)
					throw new ArgumentNullException ("initializers");

				if (!expression.Type.IsAssignableTo (type))
					throw new InvalidOperationException (
						string.Format ("{0} IsAssignableTo {1}, expression [ {2} ] : {3}", expression.Type, type, expression.NodeType, expression));

				// TODO: Quote elements if type == typeof (Expression)
			}

			return new NewArrayExpression (ExpressionType.NewArrayInit, type.MakeArrayType (), inits);
		}

		public static UnaryExpression Not (Expression expression)
		{
			return Not (expression, null);
		}

		public static UnaryExpression Not (Expression expression, MethodInfo method)
		{
			Func<Type, bool> validator = type => IsIntOrBool (type);

			method = UnaryCoreCheck ("op_LogicalNot", expression, method, validator);

			if (method == null)
				method = UnaryCoreCheck ("op_OnesComplement", expression, method, validator);

			return MakeSimpleUnary (ExpressionType.Not, expression, method);
		}

		static void CheckNotVoid (Type type)
		{
			if (type == typeof (void))
				throw new ArgumentException ("Type can't be void");
		}

		public static ParameterExpression Parameter (Type type, string name)
		{
			if (type == null)
				throw new ArgumentNullException ("type");

			CheckNotVoid (type);

			return new ParameterExpression (type, name);
		}

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

			CheckNonGenericMethod (propertyAccessor);

			if (!propertyAccessor.IsStatic) {
				if (expression == null)
					throw new ArgumentNullException ("expression");
				if (!expression.Type.IsAssignableTo (propertyAccessor.DeclaringType))
					throw new ArgumentException ("expression");
			}
			//
			// .NET does not mandate that if the property is static, that the expression must be null
			// fixes a bug exposed by Orchard's ContentItemRecordAlteration.Alteration
			// else if (expression != null)
			//		throw new ArgumentException ("expression");

			var prop = GetAssociatedProperty (propertyAccessor);
			if (prop == null)
				throw new ArgumentException (string.Format ("Method {0} has no associated property", propertyAccessor));

			return new MemberExpression (expression, prop, prop.PropertyType);
		}

		static PropertyInfo GetAssociatedProperty (MethodInfo method)
		{
			if (method == null)
				return null;

			foreach (var prop in method.DeclaringType.GetProperties (All)) {
				if (method.Equals (prop.GetGetMethod (true)))
					return prop;
				if (method.Equals (prop.GetSetMethod (true)))
					return prop;
			}

			return null;
		}

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

			var getter = property.GetGetMethod (true);
			if (getter == null)
				throw new ArgumentException ("getter");

			if (!getter.IsStatic) {
				if (expression == null)
					throw new ArgumentNullException ("expression");
				if (!expression.Type.IsAssignableTo (property.DeclaringType))
					throw new ArgumentException ("expression");
			} else if (expression != null)
				throw new ArgumentException ("expression");

			return new MemberExpression (expression, property, property.PropertyType);
		}

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

			var prop = expression.Type.GetProperty (propertyName, AllInstance);
			if (prop == null)
				throw new ArgumentException (string.Format ("No property named {0} on {1}", propertyName, expression.Type));

			return new MemberExpression (expression, prop, prop.PropertyType);
		}

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

			var prop = expression.Type.GetProperty (propertyOrFieldName, AllInstance);
			if (prop != null)
				return new MemberExpression (expression, prop, prop.PropertyType);

			var field = expression.Type.GetField (propertyOrFieldName, AllInstance);
			if (field != null)
				return new MemberExpression (expression, field, field.FieldType);

			throw new ArgumentException (string.Format ("No field or property named {0} on {1}", propertyOrFieldName, expression.Type));
		}

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

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

		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 && !type.IsNullable ())
				throw new ArgumentException ("TypeAs expect a reference or a nullable type");

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

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

			CheckNotVoid (type);

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

		public static UnaryExpression UnaryPlus (Expression expression)
		{
			return UnaryPlus (expression, null);
		}

		public static UnaryExpression UnaryPlus (Expression expression, MethodInfo method)
		{
			method = UnaryCoreCheck ("op_UnaryPlus", expression, method, type => IsNumber (type));

			return MakeSimpleUnary (ExpressionType.UnaryPlus, expression, method);
		}

		static bool IsInt (Type t)
		{
			return t == typeof (byte) || t == typeof (sbyte) ||
				t == typeof (short) || t == typeof (ushort) ||
				t == typeof (int) || t == typeof (uint) ||
				t == typeof (long) || t == typeof (ulong);
		}

		static bool IsIntOrBool (Type t)
		{
			return IsInt (t) || t == typeof (bool);
		}

		static bool IsNumber (Type t)
		{
			if (IsInt (t))
				return true;

			return t == typeof (float) || t == typeof (double);
		}

		static bool IsSignedNumber (Type t)
		{
			return IsNumber (t) && !IsUnsigned (t);
		}

		internal static bool IsUnsigned (Type t)
		{
#if !TARGET_JVM
			if (t.IsPointer)
				return IsUnsigned (t.GetElementType ());

#endif
			return t == typeof (ushort) ||
				t == typeof (uint) ||
				t == typeof (ulong) ||
				t == typeof (byte);
		}

		//
		// This method must be overwritten by derived classes to
		// compile the expression
		//
		internal virtual void Emit (EmitContext ec)
		{
			throw new NotImplementedException (String.Format ("Emit method is not implemented in expression type {0}", GetType ()));
		}
	}
}