2001-09-18 Miguel de Icaza <miguel@ximian.com>

[mono.git] / mcs / mcs / expression.cs

//
// expression.cs: Expression representation for the IL tree.
//
// Author:
//   Miguel de Icaza (miguel@ximian.com)
//
// (C) 2001 Ximian, Inc.
//
namespace CIR {
        using System.Collections;
        using System.Diagnostics;
        using System;
        using System.Reflection;
        using System.Reflection.Emit;

        // <remarks>
        //   The ExprClass class contains the is used to pass the 
        //   classification of an expression (value, variable, namespace,
        //   type, method group, property access, event access, indexer access,
        //   nothing).
        // </remarks>
        public enum ExprClass {
                Invalid,
                
                Value, Variable, Namespace, Type,
                MethodGroup, PropertyAccess,
                EventAccess, IndexerAccess, Nothing, 
        }

        // <remarks>
        //   Base class for expressions
        // </remarks>
        public abstract class Expression {
                protected ExprClass eclass;
                protected Type      type;
                
                public Type Type {
                        get {
                                return type;
                        }

                        set {
                                type = value;
                        }
                }

                public ExprClass ExprClass {
                        get {
                                return eclass;
                        }

                        set {
                                eclass = value;
                        }
                }

                public abstract Expression Resolve (TypeContainer tc);
                public abstract void Emit (EmitContext ec);
                
                // <summary>
                //   Protected constructor.  Only derivate types should
                //   be able to be created
                // </summary>

                protected Expression ()
                {
                        eclass = ExprClass.Invalid;
                        type = null;
                }

                // 
                // Returns a fully formed expression after a MemberLookup
                //
                static Expression ExprClassFromMemberInfo (MemberInfo mi)
                {
                        if (mi is EventInfo){
                                return new EventExpr ((EventInfo) mi);
                        } else if (mi is FieldInfo){
                                return new FieldExpr ((FieldInfo) mi);
                        } else if (mi is PropertyInfo){
                                return new PropertyExpr ((PropertyInfo) mi);
                        } else if (mi is Type)
                                return new TypeExpr ((Type) mi);

                        return null;
                }
                
                //
                // FIXME: Probably implement a cache for (t,name,current_access_set)?
                //
                // FIXME: We need to cope with access permissions here, or this wont
                // work!
                //
                // This code could use some optimizations, but we need to do some
                // measurements.  For example, we could use a delegate to `flag' when
                // something can not any longer be a method-group (because it is something
                // else).
                //
                // Return values:
                //     If the return value is an Array, then it is an array of
                //     MethodBases
                //   
                //     If the return value is an MemberInfo, it is anything, but a Method
                //
                //     null on error.
                //
                // FIXME: When calling MemberLookup inside an `Invocation', we should pass
                // the arguments here and have MemberLookup return only the methods that
                // match the argument count/type, unlike we are doing now (we delay this
                // decision).
                //
                // This is so we can catch correctly attempts to invoke instance methods
                // from a static body (scan for error 120 in ResolveSimpleName).
                //
                public static Expression MemberLookup (RootContext rc, Type t, string name,
                                                          bool same_type, MemberTypes mt, BindingFlags bf)
                {
                        if (same_type)
                                bf |= BindingFlags.NonPublic;

                        MemberInfo [] mi = rc.TypeManager.FindMembers (t, mt, bf, Type.FilterName, name);

                        if (mi == null)
                                return null;
                        
                        if (mi.Length == 1 && !(mi [0] is MethodBase))
                                return Expression.ExprClassFromMemberInfo (mi [0]);
                        
                        for (int i = 0; i < mi.Length; i++)
                                if (!(mi [i] is MethodBase)){
                                        rc.Report.Error (-5, "Do not know how to reproduce this case: " + 
                                                         "Methods and non-Method with the same name, report this please");

                                        for (i = 0; i < mi.Length; i++){
                                                Type tt = mi [i].GetType ();

                                                Console.WriteLine (i + ": " + mi [i]);
                                                while (tt != TypeManager.object_type){
                                                        Console.WriteLine (tt);
                                                        tt = tt.BaseType;
                                                }
                                        }
                                }

                        return new MethodGroupExpr (mi);
                }

                public const MemberTypes AllMemberTypes =
                        MemberTypes.Constructor |
                        MemberTypes.Event       |
                        MemberTypes.Field       |
                        MemberTypes.Method      |
                        MemberTypes.NestedType  |
                        MemberTypes.Property;
                
                public const BindingFlags AllBindingsFlags =
                        BindingFlags.Public |
                        BindingFlags.Static |
                        BindingFlags.Instance;

                public static Expression MemberLookup (RootContext rc, Type t, string name,
                                                       bool same_type)
                {
                        return MemberLookup (rc, t, name, same_type, AllMemberTypes, AllBindingsFlags);
                }
                
                // <summary>
                //   Resolves the E in `E.I' side for a member_access
                //
                // This is suboptimal and should be merged with ResolveMemberAccess
                static Expression ResolvePrimary (TypeContainer tc, string name)
                {
                        int dot_pos = name.LastIndexOf (".");

                        if (tc.RootContext.IsNamespace (name))
                                return new NamespaceExpr (name);

                        if (dot_pos != -1){
                        } else {
                                Type t = tc.LookupType (name, false);

                                if (t != null)
                                        return new TypeExpr (t);
                        }

                        return null;
                }
                        
                static public Expression ResolveMemberAccess (TypeContainer tc, string name)
                {
                        Expression left_e;
                        int dot_pos = name.LastIndexOf (".");
                        string left = name.Substring (0, dot_pos);
                        string right = name.Substring (dot_pos + 1);

                        left_e = ResolvePrimary (tc, left);
                        if (left_e == null)
                                return null;

                        switch (left_e.ExprClass){
                        case ExprClass.Type:
                                return  MemberLookup (tc.RootContext,
                                                      left_e.Type, right,
                                                      left_e.Type == tc.TypeBuilder);
                                
                        case ExprClass.Namespace:
                        case ExprClass.PropertyAccess:
                        case ExprClass.IndexerAccess:
                        case ExprClass.Variable:
                        case ExprClass.Value:
                        case ExprClass.Nothing:
                        case ExprClass.EventAccess:
                        case ExprClass.MethodGroup:
                        case ExprClass.Invalid:
                                tc.RootContext.Report.Error (-1000,
                                                             "Internal compiler error, should have " +
                                                             "got these handled before");
                                break;
                        }
                        
                        return null;
                }

                static public Expression ImplicitReferenceConversion (Expression expr, Type target_type)
                {
                        Type expr_type = expr.Type;
                        
                        if (target_type == TypeManager.object_type) {
                                if (expr_type.IsClass)
                                        return new EmptyCast (expr, target_type);
                                if (expr_type.IsValueType)
                                        return new BoxedCast (expr, target_type);
                        } else if (expr_type.IsSubclassOf (target_type))
                                return new EmptyCast (expr, target_type);
                        else 
                                // FIXME: missing implicit reference conversions:
                                // 
                                // from any class-type S to any interface-type T.
                                // from any interface type S to interface-type T.
                                // from an array-type S to an array-type of type T
                                // from an array-type to System.Array
                                // from any delegate type to System.Delegate
                                // from any array-type or delegate type into System.ICloneable.
                                // from the null type to any reference-type.
                                     
                                return null;

                        return null;
                }
                       
                // <summary>
                //   Converts implicitly the resolved expression `expr' into the
                //   `target_type'.  It returns a new expression that can be used
                //   in a context that expects a `target_type'. 
                // </summary>
                static public Expression ConvertImplicit (Expression expr, Type target_type)
                {
                        Type expr_type = expr.Type;

                        if (expr_type == target_type){
                                Console.WriteLine ("Hey, ConvertImplicit was called with no job to do");
                                return expr;
                        }

                        //
                        // Step 1: Perform implicit conversions as found on expr.Type
                        //

                        //
                        // Step 2: Built-in conversions.
                        //
                        if (expr_type == TypeManager.sbyte_type){
                                //
                                // From sbyte to short, int, long, float, double.
                                //
                                if (target_type == TypeManager.int32_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (target_type == TypeManager.short_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
                        } else if (expr_type == TypeManager.byte_type){
                                //
                                // From byte to short, ushort, int, uint, long, ulong, float, double
                                // 
                                if ((target_type == TypeManager.short_type) ||
                                    (target_type == TypeManager.ushort_type) ||
                                    (target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.uint32_type))
                                        return new EmptyCast (expr, target_type);

                                if (target_type == TypeManager.uint64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                        } else if (expr_type == TypeManager.short_type){
                                //
                                // From short to int, long, float, double
                                // 
                                if (target_type == TypeManager.int32_type)
                                        return new EmptyCast (expr, target_type);
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                        } else if (expr_type == TypeManager.ushort_type){
                                //
                                // From ushort to int, uint, long, ulong, float, double
                                //
                                if ((target_type == TypeManager.uint32_type) ||
                                    (target_type == TypeManager.uint64_type))
                                        return new EmptyCast (expr, target_type);
                                        
                                if (target_type == TypeManager.int32_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                        } else if (expr_type == TypeManager.int32_type){
                                //
                                // From int to long, float, double
                                //
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                        } else if (expr_type == TypeManager.uint32_type){
                                //
                                // From uint to long, ulong, float, double
                                //
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (target_type == TypeManager.uint64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
                                                               OpCodes.Conv_R8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
                                                               OpCodes.Conv_R4);
                        } else if ((expr_type == TypeManager.uint64_type) ||
                                   (expr_type == TypeManager.int64_type)){
                                //
                                // From long to float, double
                                //
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
                                                               OpCodes.Conv_R8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
                                                               OpCodes.Conv_R4);        
                        } else if (expr_type == TypeManager.char_type){
                                //
                                // From char to ushort, int, uint, long, ulong, float, double
                                // 
                                if ((target_type == TypeManager.ushort_type) ||
                                    (target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.uint32_type))
                                        return new EmptyCast (expr, target_type);
                                if (target_type == TypeManager.uint64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                        } else
                                return ImplicitReferenceConversion (expr, target_type);

                        

                        //
                        //  Could not find an implicit cast.
                        //
                        return null;
                }

                // <summary>
                //   Performs an explicit conversion of the expression `expr' whose
                //   type is expr.Type to `target_type'.
                // </summary>
                static public Expression ConvertExplicit (Expression expr, Type target_type)
                {
                        return expr;
                }
                
        }

        // <summary>
        //   This kind of cast is used to encapsulate the child
        //   whose type is child.Type into an expression that is
        //   reported to return "return_type".  This is used to encapsulate
        //   expressions which have compatible types, but need to be dealt
        //   at higher levels with.
        //
        //   For example, a "byte" expression could be encapsulated in one
        //   of these as an "unsigned int".  The type for the expression
        //   would be "unsigned int".
        //
        // </summary>
        
        public class EmptyCast : Expression {
                protected Expression child;

                public EmptyCast (Expression child, Type return_type)
                {
                        ExprClass = child.ExprClass;
                        type = return_type;
                        this.child = child;
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        child.Emit (ec);
                }                       
        }

        public class BoxedCast : EmptyCast {

                public BoxedCast (Expression expr, Type target_type)
                        : base (expr, target_type)
                {
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        base.Emit (ec);
                        ec.ig.Emit (OpCodes.Box, child.Type);
                }
        }
        

        // <summary>
        //   This kind of cast is used to encapsulate a child expression
        //   that can be trivially converted to a target type using one or 
        //   two opcodes.  The opcodes are passed as arguments.
        // </summary>
        public class OpcodeCast : EmptyCast {
                OpCode op, op2;
                bool second_valid;
                
                public OpcodeCast (Expression child, Type return_type, OpCode op)
                        : base (child, return_type)
                        
                {
                        this.op = op;
                        second_valid = false;
                }

                public OpcodeCast (Expression child, Type return_type, OpCode op, OpCode op2)
                        : base (child, return_type)
                        
                {
                        this.op = op;
                        this.op2 = op2;
                        second_valid = true;
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        base.Emit (ec);
                        ec.ig.Emit (op);

                        if (second_valid)
                                ec.ig.Emit (op2);
                }                       
                
        }
        
        public class Unary : Expression {
                public enum Operator {
                        Plus, Minus, Negate, BitComplement,
                        Indirection, AddressOf, PreIncrement,
                        PreDecrement, PostIncrement, PostDecrement
                }

                Operator   oper;
                Expression expr;
                
                public Unary (Operator op, Expression expr)
                {
                        this.oper = op;
                        this.expr = expr;
                }

                public Expression Expr {
                        get {
                                return expr;
                        }

                        set {
                                expr = value;
                        }
                }

                public Operator Oper {
                        get {
                                return oper;
                        }

                        set {
                                oper = value;
                        }
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        // FIXME: Implement;
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                }
        }

        public class Probe : Expression {
                string probe_type;
                Expression expr;
                Operator oper;

                public enum Operator {
                        Is, As
                }
                
                public Probe (Operator oper, Expression expr, string probe_type)
                {
                        this.oper = oper;
                        this.probe_type = probe_type;
                        this.expr = expr;
                }

                public Operator Oper {
                        get {
                                return oper;
                        }
                }

                public Expression Expr {
                        get {
                                return expr;
                        }
                }

                public string ProbeType {
                        get {
                                return probe_type;
                        }
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        // FIXME: Implement;
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                }
        }
        
        public class Cast : Expression {
                string target_type;
                Expression expr;
                
                public Cast (string cast_type, Expression expr)
                {
                        this.target_type = target_type;
                        this.expr = expr;
                }

                public string TargetType {
                        get {
                                return target_type;
                        }
                }

                public Expression Expr {
                        get {
                                return expr;
                        }
                        set {
                                expr = value;
                        }
                }
                
                public override Expression Resolve (TypeContainer tc)
                {
                        // FIXME: Implement;
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                }
        }

        public class Binary : Expression {
                public enum Operator {
                        Multiply, Divide, Modulo,
                        Add, Subtract,
                        ShiftLeft, ShiftRight,
                        LessThan, GreaterThan, LessOrEqual, GreaterOrEqual, 
                        Equal, NotEqual,
                        BitwiseAnd,
                        ExclusiveOr,
                        BitwiseOr,
                        LogicalAnd,
                        LogicalOr
                }

                Operator oper;
                Expression left, right;
                MethodBase method;
                ArrayList  Arguments;
                

                public Binary (Operator oper, Expression left, Expression right)
                {
                        this.oper = oper;
                        this.left = left;
                        this.right = right;
                }

                public Operator Oper {
                        get {
                                return oper;
                        }
                        set {
                                oper = value;
                        }
                }
                
                public Expression Left {
                        get {
                                return left;
                        }
                        set {
                                left = value;
                        }
                }

                public Expression Right {
                        get {
                                return right;
                        }
                        set {
                                right = value;
                        }
                }


                // <summary>
                //   Retruns a stringified representation of the Operator
                // </summary>
                string OperName ()
                {
                        switch (oper){
                        case Operator.Multiply:
                                return "*";
                        case Operator.Divide:
                                return "/";
                        case Operator.Modulo:
                                return "%";
                        case Operator.Add:
                                return "+";
                        case Operator.Subtract:
                                return "-";
                        case Operator.ShiftLeft:
                                return "<<";
                        case Operator.ShiftRight:
                                return ">>";
                        case Operator.LessThan:
                                return "<";
                        case Operator.GreaterThan:
                                return ">";
                        case Operator.LessOrEqual:
                                return "<=";
                        case Operator.GreaterOrEqual:
                                return ">=";
                        case Operator.Equal:
                                return "==";
                        case Operator.NotEqual:
                                return "!=";
                        case Operator.BitwiseAnd:
                                return "&";
                        case Operator.BitwiseOr:
                                return "|";
                        case Operator.ExclusiveOr:
                                return "^";
                        case Operator.LogicalOr:
                                return "||";
                        case Operator.LogicalAnd:
                                return "&&";
                        }

                        return oper.ToString ();
                }

                Expression ForceConversion (Expression expr, Type target_type)
                {
                        if (expr.Type == target_type)
                                return expr;

                        return ConvertImplicit (expr, target_type);
                }
                
                //
                // Note that handling the case l == Decimal || r == Decimal
                // is taken care of by the Step 1 Operator Overload resolution.
                //
                void DoNumericPromotions (TypeContainer tc, Type l, Type r)
                {
                        if (l == TypeManager.double_type || r == TypeManager.double_type){
                                //
                                // If either operand is of type double, the other operand is
                                // conveted to type double.
                                //
                                if (r != TypeManager.double_type)
                                        right = ConvertImplicit (right, TypeManager.double_type);
                                if (l != TypeManager.double_type)
                                        left = ConvertImplicit (left, TypeManager.double_type);
                                
                                type = TypeManager.double_type;
                        } else if (l == TypeManager.float_type || r == TypeManager.float_type){
                                //
                                // if either operand is of type float, th eother operand is
                                // converd to type float.
                                //
                                if (r != TypeManager.double_type)
                                        right = ConvertImplicit (right, TypeManager.float_type);
                                if (l != TypeManager.double_type)
                                        left = ConvertImplicit (left, TypeManager.float_type);
                                type = TypeManager.float_type;
                        } else if (l == TypeManager.uint64_type || r == TypeManager.uint64_type){
                                //
                                // If either operand is of type ulong, the other operand is
                                // converted to type ulong.  or an error ocurrs if the other
                                // operand is of type sbyte, short, int or long
                                //
                                Type other = null;
                                
                                if (l == TypeManager.uint64_type)
                                        other = r;
                                else if (r == TypeManager.uint64_type)
                                        other = l;

                                if ((other == TypeManager.sbyte_type) ||
                                    (other == TypeManager.short_type) ||
                                    (other == TypeManager.int32_type) ||
                                    (other == TypeManager.int64_type)){
                                        string oper = OperName ();
                                        
                                        tc.RootContext.Report.Error (34, "Operator `" + OperName ()
                                                                     + "' is ambiguous on operands of type `"
                                                                     + TypeManager.CSharpName (l) + "' "
                                                                     + "and `" + TypeManager.CSharpName (r)
                                                                     + "'");
                                }
                                type = TypeManager.uint64_type;
                        } else if (l == TypeManager.int64_type || r == TypeManager.int64_type){
                                //
                                // If either operand is of type long, the other operand is converted
                                // to type long.
                                //
                                if (l != TypeManager.int64_type)
                                        left = ConvertImplicit (left, TypeManager.int64_type);
                                if (r != TypeManager.int64_type)
                                        right = ConvertImplicit (right, TypeManager.int64_type);

                                type = TypeManager.int64_type;
                        } else if (l == TypeManager.uint32_type || r == TypeManager.uint32_type){
                                //
                                // If either operand is of type uint, and the other
                                // operand is of type sbyte, short or int, othe operands are
                                // converted to type long.
                                //
                                Type other = null;
                                
                                if (l == TypeManager.uint32_type)
                                        other = r;
                                else if (r == TypeManager.uint32_type)
                                        other = l;

                                if ((other == TypeManager.sbyte_type) ||
                                    (other == TypeManager.short_type) ||
                                    (other == TypeManager.int32_type)){
                                        left = ForceConversion (left, TypeManager.int64_type);
                                        right = ForceConversion (right, TypeManager.int64_type);
                                        type = TypeManager.int64_type;
                                } else {
                                        //
                                        // if either operand is of type uint, the other
                                        // operand is converd to type uint
                                        //
                                        left = ForceConversion (left, TypeManager.uint32_type);
                                        right = ForceConversion (left, TypeManager.uint32_type);
                                        type = TypeManager.uint32_type;
                                } 
                        } else {
                                left = ForceConversion (left, TypeManager.int32_type);
                                right = ForceConversion (right, TypeManager.int32_type);
                                type = TypeManager.int32_type;
                        }
                }

                void error19 (TypeContainer tc)
                {
                        tc.RootContext.Report.Error (
                                19,
                                "Operator " + OperName () + " cannot be applied to operands of type `" +
                                TypeManager.CSharpName (left.Type) + "' and `" +
                                TypeManager.CSharpName (right.Type) + "'");
                                                     
                }
                
                Expression CheckShiftArguments (TypeContainer tc)
                {
                        Expression e;
                        Type l = left.Type;
                        Type r = right.Type;

                        e = ForceConversion (right, TypeManager.int32_type);
                        if (e == null){
                                error19 (tc);
                                return null;
                        }
                        right = e;

                        if (((e = ConvertImplicit (left, TypeManager.int32_type)) != null) ||
                            ((e = ConvertImplicit (left, TypeManager.uint32_type)) != null) ||
                            ((e = ConvertImplicit (left, TypeManager.int64_type)) != null) ||
                            ((e = ConvertImplicit (left, TypeManager.uint64_type)) != null)){
                                left = e;

                                return this;
                        }
                        error19 (tc);
                        return null;
                }
                
                Expression ResolveOperator (TypeContainer tc)
                {
                        Type l = left.Type;
                        Type r = right.Type;

                        //
                        // Step 1: Perform Operator Overload location
                        //
                        Expression left_expr, right_expr;
                        
                        string op = "Operator" + oper;

                        left_expr = MemberLookup (tc.RootContext, l, op, false);

                        if (!(left_expr is MethodGroupExpr)){
                                // FIXME: Find proper error
                                tc.RootContext.Report.Error (118, "Did find something that is not a method");
                                return null;
                        }

                        right_expr = MemberLookup (tc.RootContext, r, op, false);

                        if (!(right_expr is MethodGroupExpr)){
                                // FIXME: Find proper error
                                tc.RootContext.Report.Error (118, "Did find something that is not a method");
                                return null;
                        }

                        if (left_expr != null || right_expr != null) {
                                //
                                // Now we need to form the union of these two sets and
                                // then call OverloadResolve on that.
                                //
                                MethodGroupExpr left_set = null, right_set = null;
                                int length1 = 0, length2 = 0;
                                
                                if (left_expr != null) {
                                        left_set = (MethodGroupExpr) left_expr;
                                        length1 = left_set.Methods.Length;
                                }

                                if (right_expr != null) {
                                        right_set = (MethodGroupExpr) right_expr;
                                        length2 = right_set.Methods.Length;
                                }

                                MemberInfo [] mi = new MemberInfo [length1 + length2];
                                if (left_set != null)
                                        left_set.Methods.CopyTo (mi, 0);
                                if (right_set != null)
                                        right_set.Methods.CopyTo (mi, length1);
                                
                                MethodGroupExpr union = new MethodGroupExpr (mi);
                                
                                Arguments = new ArrayList ();
                                Arguments.Add (new Argument (left, Argument.AType.Expression));
                                Arguments.Add (new Argument (right, Argument.AType.Expression));

                                method = Invocation.OverloadResolve (union, Arguments);
                                if (method != null)
                                        return this;

                        }

                        //
                        // Step 2: Default operations on CLI native types.
                        //
                        
                        // Only perform numeric promotions on:
                        // +, -, *, /, %, &, |, ^, ==, !=, <, >, <=, >=
                        //
                        if (oper == Operator.ShiftLeft || oper == Operator.ShiftRight){
                                return CheckShiftArguments (tc);
                        } else if (oper == Operator.LogicalOr || oper == Operator.LogicalAnd){

                                if (l != TypeManager.bool_type || r != TypeManager.bool_type)
                                        error19 (tc);
                        } else
                                DoNumericPromotions (tc, l, r);

                        if (left == null || right == null)
                                return null;

                        if (oper == Operator.BitwiseAnd ||
                            oper == Operator.BitwiseOr ||
                            oper == Operator.ExclusiveOr){
                                if (!((l == TypeManager.int32_type) ||
                                      (l == TypeManager.uint32_type) ||
                                      (l == TypeManager.int64_type) ||
                                      (l == TypeManager.uint64_type))){
                                        error19 (tc);
                                        return null;
                                }
                        }

                        if (oper == Operator.Equal ||
                            oper == Operator.NotEqual ||
                            oper == Operator.LessOrEqual ||
                            oper == Operator.LessThan ||
                            oper == Operator.GreaterOrEqual ||
                            oper == Operator.GreaterThan){
                                type = TypeManager.bool_type;
                        }
                        
                        return this;
                }
                
                public override Expression Resolve (TypeContainer tc)
                {
                        left = left.Resolve (tc);
                        right = right.Resolve (tc);

                        if (left == null || right == null)
                                return null;

                        return ResolveOperator (tc);
                }

                public bool IsBranchable ()
                {
                        if (oper == Operator.Equal ||
                            oper == Operator.NotEqual ||
                            oper == Operator.LessThan ||
                            oper == Operator.GreaterThan ||
                            oper == Operator.LessOrEqual ||
                            oper == Operator.GreaterOrEqual){
                                return true;
                        } else
                                return false;
                }

                // <summary>
                //   This entry point is used by routines that might want
                //   to emit a brfalse/brtrue after an expression, and instead
                //   they could use a more compact notation.
                //
                //   Typically the code would generate l.emit/r.emit, followed
                //   by the comparission and then a brtrue/brfalse.  The comparissions
                //   are sometimes inneficient (there are not as complete as the branches
                //   look for the hacks in Emit using double ceqs).
                //
                //   So for those cases we provide EmitBranchable that can emit the
                //   branch with the test
                // </summary>
                public void EmitBranchable (EmitContext ec, int target)
                {
                        OpCode opcode;
                        bool close_target = false;
                        
                        left.Emit (ec);
                        right.Emit (ec);
                        
                        switch (oper){
                        case Operator.Equal:
                                if (close_target)
                                        opcode = OpCodes.Beq_S;
                                else
                                        opcode = OpCodes.Beq;
                                break;

                        case Operator.NotEqual:
                                if (close_target)
                                        opcode = OpCodes.Bne_Un_S;
                                else
                                        opcode = OpCodes.Bne_Un;
                                break;

                        case Operator.LessThan:
                                if (close_target)
                                        opcode = OpCodes.Blt_S;
                                else
                                        opcode = OpCodes.Blt;
                                break;

                        case Operator.GreaterThan:
                                if (close_target)
                                        opcode = OpCodes.Bgt_S;
                                else
                                        opcode = OpCodes.Bgt;
                                break;

                        case Operator.LessOrEqual:
                                if (close_target)
                                        opcode = OpCodes.Ble_S;
                                else
                                        opcode = OpCodes.Ble;
                                break;

                        case Operator.GreaterOrEqual:
                                if (close_target)
                                        opcode = OpCodes.Bge_S;
                                else
                                        opcode = OpCodes.Ble;
                                break;

                        default:
                                throw new Exception ("EmitBranchable called on non-EmitBranchable operator: "
                                                     + oper.ToString ());
                        }

                        ec.ig.Emit (opcode, target);
                }
                
                public override void Emit (EmitContext ec)
                {
                        ILGenerator ig = ec.ig;
                        Type l = left.Type;
                        Type r = right.Type;
                        OpCode opcode;

                        if (method != null) {

                                bool is_static = method.IsStatic;

                                // FIXME : I am just not able to get this right !!
                                // There's something wrong with this part which causes
                                // an InvalidProgramException if this code is emitted
                                
                                //if (Arguments != null)
                                //      Invocation.EmitArguments (ec, Arguments);
                                
                                //if (is_static){
                                //      if (method is MethodInfo)
                                //              ig.Emit (OpCodes.Call, (MethodInfo) method);
                                //      else
                                //              ig.Emit (OpCodes.Call, (ConstructorInfo) method);
                                //} else {
                                //      if (method is MethodInfo)
                                //              ig.Emit (OpCodes.Callvirt, (MethodInfo) method);
                                //      else
                                //              ig.Emit (OpCodes.Callvirt, (ConstructorInfo) method);
                                //}
                                
                                //return;
                        }
                        
                        left.Emit (ec);
                        right.Emit (ec);

                        switch (oper){
                        case Operator.Multiply:
                                if (ec.CheckState){
                                        if (l == TypeManager.int32_type || l == TypeManager.int64_type)
                                                opcode = OpCodes.Mul_Ovf;
                                        else if (l==TypeManager.uint32_type || l==TypeManager.uint64_type)
                                                opcode = OpCodes.Mul_Ovf_Un;
                                        else
                                                opcode = OpCodes.Mul;
                                } else
                                        opcode = OpCodes.Mul;

                                break;

                        case Operator.Divide:
                                if (l == TypeManager.uint32_type || l == TypeManager.uint64_type)
                                        opcode = OpCodes.Div_Un;
                                else
                                        opcode = OpCodes.Div;
                                break;

                        case Operator.Modulo:
                                if (l == TypeManager.uint32_type || l == TypeManager.uint64_type)
                                        opcode = OpCodes.Rem_Un;
                                else
                                        opcode = OpCodes.Rem;
                                break;

                        case Operator.Add:
                                if (ec.CheckState){
                                        if (l == TypeManager.int32_type || l == TypeManager.int64_type)
                                                opcode = OpCodes.Add_Ovf;
                                        else if (l==TypeManager.uint32_type || l==TypeManager.uint64_type)
                                                opcode = OpCodes.Add_Ovf_Un;
                                        else
                                                opcode = OpCodes.Mul;
                                } else
                                        opcode = OpCodes.Add;
                                break;

                        case Operator.Subtract:
                                if (ec.CheckState){
                                        if (l == TypeManager.int32_type || l == TypeManager.int64_type)
                                                opcode = OpCodes.Sub_Ovf;
                                        else if (l==TypeManager.uint32_type || l==TypeManager.uint64_type)
                                                opcode = OpCodes.Sub_Ovf_Un;
                                        else
                                                opcode = OpCodes.Sub;
                                } else
                                        opcode = OpCodes.Sub;
                                break;

                        case Operator.ShiftRight:
                                opcode = OpCodes.Shr;
                                break;
                                
                        case Operator.ShiftLeft:
                                opcode = OpCodes.Shl;
                                break;

                        case Operator.Equal:
                                opcode = OpCodes.Ceq;
                                break;

                        case Operator.NotEqual:
                                ec.ig.Emit (OpCodes.Ceq);
                                ec.ig.Emit (OpCodes.Ldc_I4_0);
                                
                                opcode = OpCodes.Ceq;
                                break;

                        case Operator.LessThan:
                                opcode = OpCodes.Clt;
                                break;

                        case Operator.GreaterThan:
                                opcode = OpCodes.Cgt;
                                break;

                        case Operator.LessOrEqual:
                                ec.ig.Emit (OpCodes.Cgt);
                                ec.ig.Emit (OpCodes.Ldc_I4_0);
                                
                                opcode = OpCodes.Ceq;
                                break;

                        case Operator.GreaterOrEqual:
                                ec.ig.Emit (OpCodes.Clt);
                                ec.ig.Emit (OpCodes.Ldc_I4_1);
                                
                                opcode = OpCodes.Sub;
                                break;

                        case Operator.LogicalOr:
                        case Operator.BitwiseOr:
                                opcode = OpCodes.Or;
                                break;

                        case Operator.LogicalAnd:
                        case Operator.BitwiseAnd:
                                opcode = OpCodes.And;
                                break;

                        case Operator.ExclusiveOr:
                                opcode = OpCodes.Xor;
                                break;

                        default:
                                throw new Exception ("This should not happen: Operator = "
                                                     + oper.ToString ());
                        }

                        ec.ig.Emit (opcode);
                }
        }

        public class Conditional : Expression {
                Expression expr, trueExpr, falseExpr;
                
                public Conditional (Expression expr, Expression trueExpr, Expression falseExpr)
                {
                        this.expr = expr;
                        this.trueExpr = trueExpr;
                        this.falseExpr = falseExpr;
                }

                public Expression Expr {
                        get {
                                return expr;
                        }
                }

                public Expression TrueExpr {
                        get {
                                return trueExpr;
                        }
                }

                public Expression FalseExpr {
                        get {
                                return falseExpr;
                        }
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        // FIXME: Implement;
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                }
        }

        public class SimpleName : Expression {
                string name;
                
                public SimpleName (string name)
                {
                        this.name = name;
                }

                public string Name {
                        get {
                                return name;
                        }
                }

                //
                // Checks whether we are trying to access an instance
                // property, method or field from a static body.
                //
                Expression MemberStaticCheck (Report r, Expression e)
                {
                        if (e is FieldExpr){
                                FieldInfo fi = ((FieldExpr) e).FieldInfo;
                                
                                if (!fi.IsStatic){
                                        r.Error (120,
                                                 "An object reference is required " +
                                                 "for the non-static field `"+name+"'");
                                        return null;
                                }
                        } else if (e is MethodGroupExpr){
                                // FIXME: Pending reorganization of MemberLookup
                                // Basically at this point we should have the
                                // best match already selected for us, and
                                // we should only have to check a *single*
                                // Method for its static on/off bit.
                                return e;
                        } else if (e is PropertyExpr){
                                if (!((PropertyExpr) e).IsStatic){
                                        r.Error (120,
                                                 "An object reference is required " +
                                                 "for the non-static property access `"+
                                                 name+"'");
                                        return null;
                                }
                        }

                        return e;
                }
                
                //
                // 7.5.2: Simple Names. 
                //
                // Local Variables and Parameters are handled at
                // parse time, so they never occur as SimpleNames.
                //
                Expression ResolveSimpleName (TypeContainer tc)
                {
                        Expression e;
                        Report r = tc.RootContext.Report;

                        e = MemberLookup (tc.RootContext, tc.TypeBuilder, name, true);
                        if (e != null){
                                if (e is TypeExpr)
                                        return e;
                                else if (e is FieldExpr){
                                        FieldExpr fe = (FieldExpr) e;

                                        if (!fe.FieldInfo.IsStatic)
                                                fe.Instance = new This ();
                                }
                                
                                if ((tc.ModFlags & Modifiers.STATIC) != 0)
                                        return MemberStaticCheck (r, e);
                                else
                                        return e;
                        }

                        //
                        // Do step 3 of the Simple Name resolution.
                        //
                        // FIXME: implement me.
                        
                        return this;
                }
                
                //
                // SimpleName needs to handle a multitude of cases:
                //
                // simple_names and qualified_identifiers are placed on
                // the tree equally.
                //
                public override Expression Resolve (TypeContainer tc)
                {
                        if (name.IndexOf (".") != -1)
                                return ResolveMemberAccess (tc, name);
                        else
                                return ResolveSimpleName (tc);
                }

                public override void Emit (EmitContext ec)
                {
                }
        }
        
        public class LocalVariableReference : Expression {
                public readonly string Name;
                public readonly Block Block;
                
                public LocalVariableReference (Block block, string name)
                {
                        Block = block;
                        Name = name;
                        eclass = ExprClass.Variable;
                }

                public VariableInfo VariableInfo {
                        get {
                                return Block.GetVariableInfo (Name);
                        }
                }
                
                public override Expression Resolve (TypeContainer tc)
                {
                        VariableInfo vi = Block.GetVariableInfo (Name);

                        type = vi.VariableType;
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        VariableInfo vi = VariableInfo;
                        ILGenerator ig = ec.ig;
                        int idx = vi.Idx;
                        
                        switch (idx){
                        case 0:
                                ig.Emit (OpCodes.Ldloc_0);
                                break;
                                
                        case 1:
                                ig.Emit (OpCodes.Ldloc_1);
                                break;

                        case 2:
                                ig.Emit (OpCodes.Ldloc_2);
                                break;

                        case 3:
                                ig.Emit (OpCodes.Ldloc_3);
                                break;

                        default:
                                if (idx < 255)
                                        ig.Emit (OpCodes.Ldloc_S, idx);
                                else
                                        ig.Emit (OpCodes.Ldloc, idx);
                                break;
                        }
                }
        }

        public class ParameterReference : Expression {
                public readonly Parameters Pars;
                public readonly String Name;
                public readonly int Idx;
                
                public ParameterReference (Parameters pars, int idx, string name)
                {
                        Pars = pars;
                        Idx  = idx;
                        Name = name;
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        Type [] types = Pars.GetParameterInfo (tc);

                        type = types [Idx];
                        
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        if (Idx < 255)
                                ec.ig.Emit (OpCodes.Ldarg_S, Idx);
                        else
                                ec.ig.Emit (OpCodes.Ldarg, Idx);
                }
        }
        
        // <summary>
        //   Used for arguments to New(), Invocation()
        // </summary>
        public class Argument {
                public enum AType {
                        Expression,
                        Ref,
                        Out
                };

                public readonly AType Type;
                Expression expr;

                public Argument (Expression expr, AType type)
                {
                        this.expr = expr;
                        this.Type = type;
                }

                public Expression Expr {
                        get {
                                return expr;
                        }
                }

                public bool Resolve (TypeContainer tc)
                {
                        expr = expr.Resolve (tc);

                        return expr != null;
                }

                public void Emit (EmitContext ec)
                {
                        expr.Emit (ec);
                }
        }

        // <summary>
        //   Invocation of methods or delegates.
        // </summary>
        public class Invocation : Expression {
                public readonly ArrayList Arguments;
                Expression expr;
                MethodBase method = null;
                
                static Hashtable method_parameter_cache;

                static Invocation ()
                {
                        method_parameter_cache = new Hashtable ();
                }
                        
                //
                // arguments is an ArrayList, but we do not want to typecast,
                // as it might be null.
                //
                // FIXME: only allow expr to be a method invocation or a
                // delegate invocation (7.5.5)
                //
                public Invocation (Expression expr, ArrayList arguments)
                {
                        this.expr = expr;
                        Arguments = arguments;
                }

                public Expression Expr {
                        get {
                                return expr;
                        }
                }

                /// <summary>
                ///   Computes whether Argument `a' and the ParameterInfo `pi' are
                ///   compatible, and if so, how good is the match (in terms of
                ///   "better conversions" (7.4.2.3).
                ///
                ///   0   is the best possible match.
                ///   -1  represents a type mismatch.
                ///   -2  represents a ref/out mismatch.
                /// </summary>
                static int Badness (Argument a, Type t)
                {
                        if (a.Expr.Type == null){
                                throw new Exception ("Expression of type " + a.Expr + " does not resolve its type");
                        }
                        
                        if (t == a.Expr.Type) 
                                return 0;
                        
                        // FIXME: Implement implicit conversions here.
                        // FIXME: Implement better conversion here.
                        
                        return -1;
                }

                // <summary>
                //   Returns the Parameters (a ParameterData interface) for the
                //   Method `mb'
                // </summary>
                static ParameterData GetParameterData (MethodBase mb)
                {
                        object pd = method_parameter_cache [mb];

                        if (pd != null)
                                return (ParameterData) pd;

                        if (mb is MethodBuilder || mb is ConstructorBuilder){
                                MethodCore mc = TypeContainer.LookupMethodByBuilder (mb);

                                InternalParameters ip = mc.ParameterInfo;
                                method_parameter_cache [mb] = ip;

                                return (ParameterData) ip;
                        } else {
                                ParameterInfo [] pi = mb.GetParameters ();
                                ReflectionParameters rp = new ReflectionParameters (pi);
                                method_parameter_cache [mb] = rp;

                                return (ParameterData) rp;
                        }
                }
                
                // <summary>
                //   Find the Applicable Function Members (7.4.2.1)
                //
                //   me: Method Group expression with the members to select.
                //       it might contain constructors or methods (or anything
                //       that maps to a method).
                //
                //   Arguments: ArrayList containing resolved Argument objects.
                //
                //   Returns: The MethodBase (either a ConstructorInfo or a MethodInfo)
                //            that is the best match of me on Arguments.
                //
                // </summary>
                public static MethodBase OverloadResolve (MethodGroupExpr me, ArrayList Arguments)
                {
                        ArrayList afm = new ArrayList ();
                        int best_match = 10000;
                        int best_match_idx = -1;
                        MethodBase method = null;
                        int argument_count;

                        if (Arguments == null)
                                argument_count = 0;
                        else
                                argument_count = Arguments.Count;

                        for (int i = me.Methods.Length; i > 0; ){
                                i--;
                                MethodBase mb = me.Methods [i];
                                ParameterData pd;

                                pd = GetParameterData (mb);

                                // If this is the case, we have a method with no args - presumably
                                if (pd == null && argument_count == 0)
                                        return me.Methods [0];

                                //
                                // Compute how good this is
                                //
                                if (pd.Count == argument_count){
                                        int badness = 0;
                                        
                                        for (int j = argument_count; j > 0;){
                                                int x;
                                                j--;
                                                
                                                Argument a = (Argument) Arguments [j];

                                                x = Badness (a, pd.ParameterType (j));
                                                
                                                if (x < 0){
                                                        badness = best_match;
                                                        continue;
                                                }
                                                
                                                badness += x;
                                        }
                                        
                                        if (badness < best_match){
                                                best_match = badness;
                                                method = me.Methods [i];
                                                best_match_idx = i;
                                        }
                                }
                        }

                        if (best_match_idx == -1)
                                return null;
                        
                        return method;
                }

                        
                public override Expression Resolve (TypeContainer tc)
                {
                        //
                        // First, resolve the expression that is used to
                        // trigger the invocation
                        //
                        this.expr = expr.Resolve (tc);
                        if (this.expr == null)
                                return null;

                        if (!(this.expr is MethodGroupExpr)){
                                tc.RootContext.Report.Error (118,
                                       "Denotes a non-method (Detail: ExprClass=" + this.expr.ExprClass+")");
                                return null;
                        }

                        //
                        // Next, evaluate all the expressions in the argument list
                        //
                        if (Arguments != null){
                                for (int i = Arguments.Count; i > 0;){
                                        --i;
                                        Argument a = (Argument) Arguments [i];

                                        if (!a.Resolve (tc))
                                                return null;
                                }
                        }

                        method = OverloadResolve ((MethodGroupExpr) this.expr, Arguments);

                        if (method == null){
                                tc.RootContext.Report.Error (-6,
                                "Figure out error: Can not find a good function for this argument list");
                                return null;
                        }

                        if (method is MethodInfo)
                                type = ((MethodInfo)method).ReturnType;

                        return this;
                }

                public static void EmitArguments (EmitContext ec, ArrayList Arguments)
                {
                        int top;

                        if (Arguments != null)
                                top = Arguments.Count;
                        else
                                top = 0;

                        for (int i = 0; i < top; i++){
                                Argument a = (Argument) Arguments [i];

                                a.Emit (ec);
                        }
                }
                
                public override void Emit (EmitContext ec)
                {
                        bool is_static = method.IsStatic;

                        if (!is_static){
                                MethodGroupExpr mg = (MethodGroupExpr) this.expr;

                                if (mg.InstanceExpression == null){
                                        Console.WriteLine ("Internal compiler error.  Should check in the method groups for static/instance");
                                }

                                mg.InstanceExpression.Emit (ec);
                        }

                        if (Arguments != null)
                                EmitArguments (ec, Arguments);

                        if (is_static){
                                if (method is MethodInfo)
                                        ec.ig.Emit (OpCodes.Call, (MethodInfo) method);
                                else
                                        ec.ig.Emit (OpCodes.Call, (ConstructorInfo) method);
                        } else {
                                if (method is MethodInfo)
                                        ec.ig.Emit (OpCodes.Callvirt, (MethodInfo) method);
                                else
                                        ec.ig.Emit (OpCodes.Callvirt, (ConstructorInfo) method);
                        } 

                }
        }

        public class New : Expression {

                public enum NType {
                        Object,
                        Array
                };

                public readonly NType     NewType;
                public readonly ArrayList Arguments;
                public readonly string    RequestedType;
                // These are for the case when we have an array
                public readonly string    Rank;
                public readonly ArrayList Indices;
                public readonly ArrayList Initializers;
                
                MethodBase method = null;

                public New (string requested_type, ArrayList arguments)
                {
                        RequestedType = requested_type;
                        Arguments = arguments;
                        NewType = NType.Object;
                }

                public New (string requested_type, ArrayList exprs, string rank, ArrayList initializers)
                {
                        RequestedType = requested_type;
                        Indices       = exprs;
                        Rank          = rank;
                        Initializers  = initializers;
                        NewType       = NType.Array;
                }
                
                public override Expression Resolve (TypeContainer tc)
                {
                        type = tc.LookupType (RequestedType, false);

                        if (type == null)
                                return null;

                        Expression ml;

                        ml = MemberLookup (tc.RootContext, type, ".ctor", false,
                                           MemberTypes.Constructor, AllBindingsFlags);

                        if (! (ml is MethodGroupExpr)){
                                //
                                // FIXME: Find proper error
                                //
                                tc.RootContext.Report.Error (118, "Did find something that is not a method");
                                return null;
                        }
                        
                        if (Arguments != null){
                                for (int i = Arguments.Count; i > 0;){
                                        --i;
                                        Argument a = (Argument) Arguments [i];

                                        if (!a.Resolve (tc))
                                                return null;
                                }
                        }

                        method = Invocation.OverloadResolve ((MethodGroupExpr) ml, Arguments);

                        if (method == null) {
                                tc.RootContext.Report.Error (-6,
                                "New invocation: Can not find a constructor for this argument list");
                                return null;
                        }

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        Invocation.EmitArguments (ec, Arguments);
                        ec.ig.Emit (OpCodes.Newobj, (ConstructorInfo) method);
                }
        }

        //
        // Represents the `this' construct
        //
        public class This : Expression {
                public override Expression Resolve (TypeContainer tc)
                {
                        eclass = ExprClass.Variable;
                        type = tc.TypeBuilder;
                        
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        ec.ig.Emit (OpCodes.Ldarg_0);
                }
        }

        public class TypeOf : Expression {
                public readonly string QueriedType;
                
                public TypeOf (string queried_type)
                {
                        QueriedType = queried_type;
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        type = tc.LookupType (QueriedType, false);

                        if (type == null)
                                return null;
                        
                        eclass = ExprClass.Type;
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        // FIXME: Implement.
                }
        }

        public class SizeOf : Expression {
                public readonly string QueriedType;
                
                public SizeOf (string queried_type)
                {
                        this.QueriedType = queried_type;
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        // FIXME: Implement;
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                }
        }

        public class MemberAccess : Expression {
                public readonly string Identifier;
                Expression expr;
                Expression member_lookup;
                
                public MemberAccess (Expression expr, string id)
                {
                        this.expr = expr;
                        Identifier = id;
                }

                public Expression Expr {
                        get {
                                return expr;
                        }
                }
                
                public override Expression Resolve (TypeContainer tc)
                {
                        Expression new_expression = expr.Resolve (tc);

                        if (new_expression == null)
                                return null;

                        Console.WriteLine ("This is what I figured: " + expr.Type + "/" + expr.ExprClass);

                        member_lookup = MemberLookup (tc.RootContext, expr.Type, Identifier, false);

                        if (member_lookup is MethodGroupExpr){
                                MethodGroupExpr mg = (MethodGroupExpr) member_lookup;

                                //
                                // Bind the instance expression to it
                                //
                                // FIXME: This is a horrible way of detecting if it is
                                // an instance expression.  Figure out how to fix this.
                                //

                                if (expr is LocalVariableReference ||
                                    expr is ParameterReference ||
                                    expr is FieldExpr)
                                        mg.InstanceExpression = expr;
                                        
                                return member_lookup;
                        } else if (member_lookup is FieldExpr){
                                FieldExpr fe = (FieldExpr) member_lookup;

                                fe.Instance = expr;

                                return member_lookup;
                        } else
                                //
                                // FIXME: This should generate the proper node
                                // ie, for a Property Access, it should like call it
                                // and stuff.

                                return member_lookup;
                }

                public override void Emit (EmitContext ec)
                {
                }

        }

        // <summary>
        //   Nodes of type Namespace are created during the semantic
        //   analysis to resolve member_access/qualified_identifier/simple_name
        //   accesses.
        //
        //   They are born `resolved'. 
        // </summary>
        public class NamespaceExpr : Expression {
                public readonly string Name;
                
                public NamespaceExpr (string name)
                {
                        Name = name;
                        eclass = ExprClass.Namespace;
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                }
        }

        // <summary>
        //   Fully resolved expression that evaluates to a type
        // </summary>
        public class TypeExpr : Expression {
                public TypeExpr (Type t)
                {
                        Type = t;
                        eclass = ExprClass.Type;
                }

                override public Expression Resolve (TypeContainer tc)
                {
                        return this;
                }

                override public void Emit (EmitContext ec)
                {
                        
                }
        }

        // <summary>
        //   MethodGroup Expression.
        //  
        //   This is a fully resolved expression that evaluates to a type
        // </summary>
        public class MethodGroupExpr : Expression {
                public readonly MethodBase [] Methods;
                Expression instance_expression = null;
                
                public MethodGroupExpr (MemberInfo [] mi)
                {
                        Methods = new MethodBase [mi.Length];
                        mi.CopyTo (Methods, 0);
                        eclass = ExprClass.MethodGroup;
                }

                //
                // `A method group may have associated an instance expression' 
                // 
                public Expression InstanceExpression {
                        get {
                                return instance_expression;
                        }

                        set {
                                instance_expression = value;
                        }
                }
                
                override public Expression Resolve (TypeContainer tc)
                {
                        return this;
                }

                override public void Emit (EmitContext ec)
                {
                        
                }
        }
        
        public class BuiltinTypeAccess : Expression {
                public readonly string AccessBase;
                public readonly string Method;
                
                public BuiltinTypeAccess (string type, string method)
                {
                        System.Console.WriteLine ("DUDE! This type should be fully resolved!");
                        AccessBase = type;
                        Method = method;
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        // FIXME: Implement;
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                }
        }


        //   Fully resolved expression that evaluates to a Field
        // </summary>
        public class FieldExpr : Expression {
                public readonly FieldInfo FieldInfo;
                public Expression Instance;
                        
                public FieldExpr (FieldInfo fi)
                {
                        FieldInfo = fi;
                        eclass = ExprClass.Variable;
                        type = fi.FieldType;
                }

                override public Expression Resolve (TypeContainer tc)
                {
                        if (!FieldInfo.IsStatic){
                                if (Instance == null){
                                        throw new Exception ("non-static FieldExpr without instance var\n" +
                                                             "You have to assign the Instance variable\n" +
                                                             "Of the FieldExpr to set this\n");
                                }

                                Instance = Instance.Resolve (tc);
                                if (Instance == null)
                                        return null;
                                
                        }
                        return this;
                }

                override public void Emit (EmitContext ec)
                {
                        ILGenerator ig = ec.ig;

                        if (FieldInfo.IsStatic)
                                ig.Emit (OpCodes.Ldsfld, FieldInfo);
                        else {
                                Instance.Emit (ec);
                                
                                ig.Emit (OpCodes.Ldfld, FieldInfo);
                        }
                }
        }
        
        // <summary>
        //   Fully resolved expression that evaluates to a Property
        // </summary>
        public class PropertyExpr : Expression {
                public readonly PropertyInfo PropertyInfo;
                public readonly bool IsStatic;
                
                public PropertyExpr (PropertyInfo pi)
                {
                        PropertyInfo = pi;
                        eclass = ExprClass.PropertyAccess;
                        IsStatic = false;
                                
                        MethodBase [] acc = pi.GetAccessors ();

                        for (int i = 0; i < acc.Length; i++)
                                if (acc [i].IsStatic)
                                        IsStatic = true;

                        type = pi.PropertyType;
                }

                override public Expression Resolve (TypeContainer tc)
                {
                        // We are born in resolved state. 
                        return this;
                }

                override public void Emit (EmitContext ec)
                {
                        // FIXME: Implement.
                }
        }

        // <summary>
        //   Fully resolved expression that evaluates to a Property
        // </summary>
        public class EventExpr : Expression {
                public readonly EventInfo EventInfo;
                
                public EventExpr (EventInfo ei)
                {
                        EventInfo = ei;
                        eclass = ExprClass.EventAccess;
                }

                override public Expression Resolve (TypeContainer tc)
                {
                        // We are born in resolved state. 
                        return this;
                }

                override public void Emit (EmitContext ec)
                {
                        // FIXME: Implement.
                }
        }
        
        public class CheckedExpr : Expression {

                public Expression Expr;

                public CheckedExpr (Expression e)
                {
                        Expr = e;
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        Expr = Expr.Resolve (tc);

                        if (Expr == null)
                                return null;

                        eclass = Expr.ExprClass;
                        type = Expr.Type;
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        bool last_check = ec.CheckState;

                        ec.CheckState = true;
                        
                        Expr.Emit (ec);

                        ec.CheckState = last_check;
                }
                
        }

        public class UnCheckedExpr : Expression {

                public Expression Expr;

                public UnCheckedExpr (Expression e)
                {
                        Expr = e;
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        Expr = Expr.Resolve (tc);

                        if (Expr == null)
                                return null;

                        eclass = Expr.ExprClass;
                        type = Expr.Type;
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        bool last_check = ec.CheckState;

                        ec.CheckState = false;
                        
                        Expr.Emit (ec);

                        ec.CheckState = last_check;
                }
                
        }
        
        public class ElementAccess : Expression {
                
                public readonly ArrayList  Arguments;
                public readonly Expression Expr;
                
                public ElementAccess (Expression e, ArrayList e_list)
                {
                        Expr = e;
                        Arguments = e_list;
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        // FIXME : Implement
                        return this;
                }
                
                public override void Emit (EmitContext ec)
                {
                        // FIXME : Implement !
                }
                
        }
        
        public class BaseAccess : Expression {

                public enum BaseAccessType {
                        Member,
                        Indexer
                };
                
                public readonly BaseAccessType BAType;
                public readonly string         Member;
                public readonly ArrayList      Arguments;

                public BaseAccess (BaseAccessType t, string member, ArrayList args)
                {
                        BAType = t;
                        Member = member;
                        Arguments = args;
                        
                }

                public override Expression Resolve (TypeContainer tc)
                {
                        // FIXME : Implement !
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                }
        }
}