Merged into single file, added assertions

[mono.git] / mcs / mcs / cs-tokenizer.cs

//
// cs-tokenizer.cs: The Tokenizer for the C# compiler
//                  This also implements the preprocessor
//
// Author: Miguel de Icaza (miguel@gnu.org)
//         Marek Safar (marek.safar@gmail.com)
//
// Dual licensed under the terms of the MIT X11 or GNU GPL
//
// Copyright 2001, 2002 Ximian, Inc (http://www.ximian.com)
// Copyright 2004-2008 Novell, Inc
// Copyright 2011 Xamarin, Inc (http://www.xamarin.com)
//

using System;
using System.Text;
using System.Collections.Generic;
using System.Globalization;
using System.Diagnostics;
using System.Collections;

namespace Mono.CSharp
{
        /// <summary>
        ///    Tokenizer for C# source code. 
        /// </summary>

        public class Tokenizer : yyParser.yyInput
        {
                class KeywordEntry<T>
                {
                        public readonly T Token;
                        public KeywordEntry<T> Next;
                        public readonly char[] Value;

                        public KeywordEntry (string value, T token)
                        {
                                this.Value = value.ToCharArray ();
                                this.Token = token;
                        }
                }

                sealed class IdentifiersComparer : IEqualityComparer<char[]>
                {
                        readonly int length;

                        public IdentifiersComparer (int length)
                        {
                                this.length = length;
                        }

                        public bool Equals (char[] x, char[] y)
                        {
                                for (int i = 0; i < length; ++i)
                                        if (x [i] != y [i])
                                                return false;

                                return true;
                        }

                        public int GetHashCode (char[] obj)
                        {
                                int h = 0;
                                for (int i = 0; i < length; ++i)
                                        h = (h << 5) - h + obj [i];

                                return h;
                        }
                }

                //
                // This class has to be used by parser only, it reuses token
                // details after each file parse completion
                //
                public class LocatedToken
                {
                        public int row, column;
                        public string value;
                        public SourceFile file;

                        public LocatedToken ()
                        {
                        }

                        public LocatedToken (string value, Location loc)
                        {
                                this.value = value;
                                file = loc.SourceFile;
                                row = loc.Row;
                                column = loc.Column;
                        }

                        public override string ToString ()
                        {
                                return string.Format ("Token '{0}' at {1},{2}", Value, row, column);
                        }
                        
                        public Location Location {
                                get { return new Location (file, row, column); }
                        }

                        public string Value {
                                get { return value; }
                        }
                }

                public class LocatedTokenBuffer
                {
                        readonly LocatedToken[] buffer;
                        public int pos;

                        public LocatedTokenBuffer ()
                        {
                                buffer = new LocatedToken[0];
                        }

                        public LocatedTokenBuffer (LocatedToken[] buffer)
                        {
                                this.buffer = buffer ?? new LocatedToken[0];
                        }

                        public LocatedToken Create (SourceFile file, int row, int column)
                        {
                                return Create (null, file, row, column);
                        }

                        public LocatedToken Create (string value, SourceFile file, int row, int column)
                        {
                                //
                                // TODO: I am not very happy about the logic but it's the best
                                // what I could come up with for now.
                                // Ideally we should be using just tiny buffer (256 elements) which
                                // is enough to hold all details for currect stack and recycle elements
                                // poped from the stack but there is a trick needed to recycle
                                // them properly.
                                //
                                LocatedToken entry;
                                if (pos >= buffer.Length) {
                                        entry = new LocatedToken ();
                                } else {
                                        entry = buffer[pos];
                                        if (entry == null) {
                                                entry = new LocatedToken ();
                                                buffer[pos] = entry;
                                        }

                                        ++pos;
                                }
                                entry.value = value;
                                entry.file = file;
                                entry.row = row;
                                entry.column = column;
                                return entry;
                        }

                        //
                        // Used for token not required by expression evaluator
                        //
                        [Conditional ("FULL_AST")]
                        public void CreateOptional (SourceFile file, int row, int col, ref object token)
                        {
                                token = Create (file, row, col);
                        }
                }

                public enum PreprocessorDirective
                {
                        Invalid = 0,

                        Region = 1,
                        Endregion = 2,
                        If = 3 | RequiresArgument,
                        Endif = 4,
                        Elif = 5 | RequiresArgument,
                        Else = 6,
                        Define = 7 | RequiresArgument,
                        Undef = 8 | RequiresArgument,
                        Error = 9,
                        Warning = 10,
                        Pragma = 11 | CustomArgumentsParsing,
                        Line = 12 | CustomArgumentsParsing,

                        CustomArgumentsParsing = 1 << 10,
                        RequiresArgument = 1 << 11
                }

                readonly SeekableStreamReader reader;
                readonly CompilationSourceFile source_file;
                readonly CompilerContext context;

                SourceFile current_source;
                Location hidden_block_start;
                int ref_line = 1;
                int line = 1;
                int col = 0;
                int previous_col;
                int current_token;
                readonly int tab_size;
                bool handle_get_set = false;
                bool handle_remove_add = false;
                bool handle_where = false;
                bool handle_typeof = false;
                bool lambda_arguments_parsing;
                List<Location> escaped_identifiers;
                int parsing_generic_less_than;
                readonly bool doc_processing;
                readonly LocatedTokenBuffer ltb;
                
                //
                // Used mainly for parser optimizations. Some expressions for instance
                // can appear only in block (including initializer, base initializer)
                // scope only
                //
                public int parsing_block;
                internal bool query_parsing;
                
                // 
                // When parsing type only, useful for ambiguous nullable types
                //
                public int parsing_type;
                
                //
                // Set when parsing generic declaration (type or method header)
                //
                public bool parsing_generic_declaration;
                public bool parsing_generic_declaration_doc;
                
                //
                // The value indicates that we have not reach any declaration or
                // namespace yet
                //
                public int parsing_declaration;

                public bool parsing_attribute_section;

                public bool parsing_modifiers;

                //
                // The special characters to inject on streams to run the unit parser
                // in the special expression mode. Using private characters from
                // Plane Sixteen (U+100000 to U+10FFFD)
                //
                // This character is only tested just before the tokenizer is about to report
                // an error;   So on the regular operation mode, this addition will have no
                // impact on the tokenizer's performance.
                //
                
                public const int EvalStatementParserCharacter = 0x100000;
                public const int EvalCompilationUnitParserCharacter = 0x100001;
                public const int EvalUsingDeclarationsParserCharacter = 0x100002;
                public const int DocumentationXref = 0x100003;
                
                //
                // XML documentation buffer. The save point is used to divide
                // comments on types and comments on members.
                //
                StringBuilder xml_comment_buffer;

                //
                // See comment on XmlCommentState enumeration.
                //
                XmlCommentState xml_doc_state = XmlCommentState.Allowed;

                //
                // Whether tokens have been seen on this line
                //
                bool tokens_seen = false;

                //
                // Set to true once the GENERATE_COMPLETION token has bee
                // returned.   This helps produce one GENERATE_COMPLETION,
                // as many COMPLETE_COMPLETION as necessary to complete the
                // AST tree and one final EOF.
                //
                bool generated;
                
                //
                // Whether a token has been seen on the file
                // This is needed because `define' is not allowed to be used
                // after a token has been seen.
                //
                bool any_token_seen;

                //
                // Class variables
                // 
                static readonly KeywordEntry<int>[][] keywords;
                static readonly KeywordEntry<PreprocessorDirective>[][] keywords_preprocessor;
                static readonly HashSet<string> keyword_strings;
                static readonly NumberStyles styles;
                static readonly NumberFormatInfo csharp_format_info;

                // Pragma arguments
                static readonly char[] pragma_warning = "warning".ToCharArray ();
                static readonly char[] pragma_warning_disable = "disable".ToCharArray ();
                static readonly char[] pragma_warning_restore = "restore".ToCharArray ();
                static readonly char[] pragma_checksum = "checksum".ToCharArray ();
                static readonly char[] line_hidden = "hidden".ToCharArray ();
                static readonly char[] line_default = "default".ToCharArray ();

                static readonly char[] simple_whitespaces = new char[] { ' ', '\t' };

                public bool PropertyParsing {
                        get { return handle_get_set; }
                        set { handle_get_set = value; }
                }

                public bool EventParsing {
                        get { return handle_remove_add; }
                        set { handle_remove_add = value; }
                }

                public bool ConstraintsParsing {
                        get { return handle_where; }
                        set { handle_where = value; }
                }

                public bool TypeOfParsing {
                        get { return handle_typeof; }
                        set { handle_typeof = value; }
                }
        
                public XmlCommentState doc_state {
                        get { return xml_doc_state; }
                        set {
                                if (value == XmlCommentState.Allowed) {
                                        check_incorrect_doc_comment ();
                                        reset_doc_comment ();
                                }
                                xml_doc_state = value;
                        }
                }

                //
                // This is used to trigger completion generation on the parser
                public bool CompleteOnEOF;
                
                void AddEscapedIdentifier (Location loc)
                {
                        if (escaped_identifiers == null)
                                escaped_identifiers = new List<Location> ();

                        escaped_identifiers.Add (loc);
                }

                public bool IsEscapedIdentifier (ATypeNameExpression name)
                {
                        return escaped_identifiers != null && escaped_identifiers.Contains (name.Location);
                }

                //
                // Values for the associated token returned
                //
                internal int putback_char;      // Used by repl only
                object val;

                //
                // Pre-processor
                //
                const int TAKING        = 1;
                const int ELSE_SEEN     = 4;
                const int PARENT_TAKING = 8;
                const int REGION        = 16;           

                //
                // pre-processor if stack state:
                //
                Stack<int> ifstack;

                public const int MaxIdentifierLength = 512;
                public const int MaxNumberLength = 512;

                readonly char[] id_builder;
                readonly Dictionary<char[], string>[] identifiers;
                readonly char[] number_builder;
                int number_pos;

                char[] value_builder = new char[64];

                public int Line {
                        get {
                                return ref_line;
                        }
                }

                //
                // This is used when the tokenizer needs to save
                // the current position as it needs to do some parsing
                // on its own to deamiguate a token in behalf of the
                // parser.
                //
                Stack<Position> position_stack = new Stack<Position> (2);

                class Position {
                        public int position;
                        public int line;
                        public int ref_line;
                        public int col;
                        public Location hidden;
                        public int putback_char;
                        public int previous_col;
                        public Stack<int> ifstack;
                        public int parsing_generic_less_than;
                        public int current_token;
                        public object val;

                        public Position (Tokenizer t)
                        {
                                position = t.reader.Position;
                                line = t.line;
                                ref_line = t.ref_line;
                                col = t.col;
                                hidden = t.hidden_block_start;
                                putback_char = t.putback_char;
                                previous_col = t.previous_col;
                                if (t.ifstack != null && t.ifstack.Count != 0) {
                                        // There is no simple way to clone Stack<T> all
                                        // methods reverse the order
                                        var clone = t.ifstack.ToArray ();
                                        Array.Reverse (clone);
                                        ifstack = new Stack<int> (clone);
                                }
                                parsing_generic_less_than = t.parsing_generic_less_than;
                                current_token = t.current_token;
                                val = t.val;
                        }
                }

                public Tokenizer (SeekableStreamReader input, CompilationSourceFile file, ParserSession session)
                {
                        this.source_file = file;
                        this.context = file.Compiler;
                        this.current_source = file.SourceFile;
                        this.identifiers = session.Identifiers;
                        this.id_builder = session.IDBuilder;
                        this.number_builder = session.NumberBuilder;
                        this.ltb = new LocatedTokenBuffer (session.LocatedTokens);

                        reader = input;

                        putback_char = -1;

                        xml_comment_buffer = new StringBuilder ();
                        doc_processing = context.Settings.DocumentationFile != null;

                        tab_size = context.Settings.TabSize;
                }
                
                public void PushPosition ()
                {
                        position_stack.Push (new Position (this));
                }

                public void PopPosition ()
                {
                        Position p = position_stack.Pop ();

                        reader.Position = p.position;
                        ref_line = p.ref_line;
                        line = p.line;
                        col = p.col;
                        hidden_block_start = p.hidden;
                        putback_char = p.putback_char;
                        previous_col = p.previous_col;
                        ifstack = p.ifstack;
                        parsing_generic_less_than = p.parsing_generic_less_than;
                        current_token = p.current_token;
                        val = p.val;
                }

                // Do not reset the position, ignore it.
                public void DiscardPosition ()
                {
                        position_stack.Pop ();
                }
                
                static void AddKeyword (string kw, int token)
                {
                        keyword_strings.Add (kw);

                        AddKeyword (keywords, kw, token);
                }

                static void AddPreprocessorKeyword (string kw, PreprocessorDirective directive)
                {
                        AddKeyword (keywords_preprocessor, kw, directive);
                }

                static void AddKeyword<T> (KeywordEntry<T>[][] keywords, string kw, T token)
                {
                        int length = kw.Length;
                        if (keywords[length] == null) {
                                keywords[length] = new KeywordEntry<T>['z' - '_' + 1];
                        }

                        int char_index = kw[0] - '_';
                        var kwe = keywords[length][char_index];
                        if (kwe == null) {
                                keywords[length][char_index] = new KeywordEntry<T> (kw, token);
                                return;
                        }

                        while (kwe.Next != null) {
                                kwe = kwe.Next;
                        }

                        kwe.Next = new KeywordEntry<T> (kw, token);
                }

                //
                // Class initializer
                // 
                static Tokenizer ()
                {
                        keyword_strings = new HashSet<string> ();

                        // 11 is the length of the longest keyword for now
                        keywords = new KeywordEntry<int>[11][];

                        AddKeyword ("__arglist", Token.ARGLIST);
                        AddKeyword ("__makeref", Token.MAKEREF);
                        AddKeyword ("__reftype", Token.REFTYPE);
                        AddKeyword ("__refvalue", Token.REFVALUE);
                        AddKeyword ("abstract", Token.ABSTRACT);
                        AddKeyword ("as", Token.AS);
                        AddKeyword ("add", Token.ADD);
                        AddKeyword ("base", Token.BASE);
                        AddKeyword ("bool", Token.BOOL);
                        AddKeyword ("break", Token.BREAK);
                        AddKeyword ("byte", Token.BYTE);
                        AddKeyword ("case", Token.CASE);
                        AddKeyword ("catch", Token.CATCH);
                        AddKeyword ("char", Token.CHAR);
                        AddKeyword ("checked", Token.CHECKED);
                        AddKeyword ("class", Token.CLASS);
                        AddKeyword ("const", Token.CONST);
                        AddKeyword ("continue", Token.CONTINUE);
                        AddKeyword ("decimal", Token.DECIMAL);
                        AddKeyword ("default", Token.DEFAULT);
                        AddKeyword ("delegate", Token.DELEGATE);
                        AddKeyword ("do", Token.DO);
                        AddKeyword ("double", Token.DOUBLE);
                        AddKeyword ("else", Token.ELSE);
                        AddKeyword ("enum", Token.ENUM);
                        AddKeyword ("event", Token.EVENT);
                        AddKeyword ("explicit", Token.EXPLICIT);
                        AddKeyword ("extern", Token.EXTERN);
                        AddKeyword ("false", Token.FALSE);
                        AddKeyword ("finally", Token.FINALLY);
                        AddKeyword ("fixed", Token.FIXED);
                        AddKeyword ("float", Token.FLOAT);
                        AddKeyword ("for", Token.FOR);
                        AddKeyword ("foreach", Token.FOREACH);
                        AddKeyword ("goto", Token.GOTO);
                        AddKeyword ("get", Token.GET);
                        AddKeyword ("if", Token.IF);
                        AddKeyword ("implicit", Token.IMPLICIT);
                        AddKeyword ("in", Token.IN);
                        AddKeyword ("int", Token.INT);
                        AddKeyword ("interface", Token.INTERFACE);
                        AddKeyword ("internal", Token.INTERNAL);
                        AddKeyword ("is", Token.IS);
                        AddKeyword ("lock", Token.LOCK);
                        AddKeyword ("long", Token.LONG);
                        AddKeyword ("namespace", Token.NAMESPACE);
                        AddKeyword ("new", Token.NEW);
                        AddKeyword ("null", Token.NULL);
                        AddKeyword ("object", Token.OBJECT);
                        AddKeyword ("operator", Token.OPERATOR);
                        AddKeyword ("out", Token.OUT);
                        AddKeyword ("override", Token.OVERRIDE);
                        AddKeyword ("params", Token.PARAMS);
                        AddKeyword ("private", Token.PRIVATE);
                        AddKeyword ("protected", Token.PROTECTED);
                        AddKeyword ("public", Token.PUBLIC);
                        AddKeyword ("readonly", Token.READONLY);
                        AddKeyword ("ref", Token.REF);
                        AddKeyword ("remove", Token.REMOVE);
                        AddKeyword ("return", Token.RETURN);
                        AddKeyword ("sbyte", Token.SBYTE);
                        AddKeyword ("sealed", Token.SEALED);
                        AddKeyword ("set", Token.SET);
                        AddKeyword ("short", Token.SHORT);
                        AddKeyword ("sizeof", Token.SIZEOF);
                        AddKeyword ("stackalloc", Token.STACKALLOC);
                        AddKeyword ("static", Token.STATIC);
                        AddKeyword ("string", Token.STRING);
                        AddKeyword ("struct", Token.STRUCT);
                        AddKeyword ("switch", Token.SWITCH);
                        AddKeyword ("this", Token.THIS);
                        AddKeyword ("throw", Token.THROW);
                        AddKeyword ("true", Token.TRUE);
                        AddKeyword ("try", Token.TRY);
                        AddKeyword ("typeof", Token.TYPEOF);
                        AddKeyword ("uint", Token.UINT);
                        AddKeyword ("ulong", Token.ULONG);
                        AddKeyword ("unchecked", Token.UNCHECKED);
                        AddKeyword ("unsafe", Token.UNSAFE);
                        AddKeyword ("ushort", Token.USHORT);
                        AddKeyword ("using", Token.USING);
                        AddKeyword ("virtual", Token.VIRTUAL);
                        AddKeyword ("void", Token.VOID);
                        AddKeyword ("volatile", Token.VOLATILE);
                        AddKeyword ("while", Token.WHILE);
                        AddKeyword ("partial", Token.PARTIAL);
                        AddKeyword ("where", Token.WHERE);

                        // LINQ keywords
                        AddKeyword ("from", Token.FROM);
                        AddKeyword ("join", Token.JOIN);
                        AddKeyword ("on", Token.ON);
                        AddKeyword ("equals", Token.EQUALS);
                        AddKeyword ("select", Token.SELECT);
                        AddKeyword ("group", Token.GROUP);
                        AddKeyword ("by", Token.BY);
                        AddKeyword ("let", Token.LET);
                        AddKeyword ("orderby", Token.ORDERBY);
                        AddKeyword ("ascending", Token.ASCENDING);
                        AddKeyword ("descending", Token.DESCENDING);
                        AddKeyword ("into", Token.INTO);

                        // Contextual async keywords
                        AddKeyword ("async", Token.ASYNC);
                        AddKeyword ("await", Token.AWAIT);

                        keywords_preprocessor = new KeywordEntry<PreprocessorDirective>[10][];

                        AddPreprocessorKeyword ("region", PreprocessorDirective.Region);
                        AddPreprocessorKeyword ("endregion", PreprocessorDirective.Endregion);
                        AddPreprocessorKeyword ("if", PreprocessorDirective.If);
                        AddPreprocessorKeyword ("endif", PreprocessorDirective.Endif);
                        AddPreprocessorKeyword ("elif", PreprocessorDirective.Elif);
                        AddPreprocessorKeyword ("else", PreprocessorDirective.Else);
                        AddPreprocessorKeyword ("define", PreprocessorDirective.Define);
                        AddPreprocessorKeyword ("undef", PreprocessorDirective.Undef);
                        AddPreprocessorKeyword ("error", PreprocessorDirective.Error);
                        AddPreprocessorKeyword ("warning", PreprocessorDirective.Warning);
                        AddPreprocessorKeyword ("pragma", PreprocessorDirective.Pragma);
                        AddPreprocessorKeyword ("line", PreprocessorDirective.Line);

                        csharp_format_info = NumberFormatInfo.InvariantInfo;
                        styles = NumberStyles.Float;
                }

                int GetKeyword (char[] id, int id_len)
                {
                        //
                        // Keywords are stored in an array of arrays grouped by their
                        // length and then by the first character
                        //
                        if (id_len >= keywords.Length || keywords [id_len] == null)
                                return -1;

                        int first_index = id [0] - '_';
                        if (first_index > 'z' - '_')
                                return -1;

                        var kwe = keywords [id_len] [first_index];
                        if (kwe == null)
                                return -1;

                        int res;
                        do {
                                res = kwe.Token;
                                for (int i = 1; i < id_len; ++i) {
                                        if (id [i] != kwe.Value [i]) {
                                                res = 0;
                                                kwe = kwe.Next;
                                                break;
                                        }
                                }
                        } while (res == 0 && kwe != null);

                        if (res == 0)
                                return -1;

                        int next_token;
                        switch (res) {
                        case Token.GET:
                        case Token.SET:
                                if (!handle_get_set)
                                        res = -1;
                                break;
                        case Token.REMOVE:
                        case Token.ADD:
                                if (!handle_remove_add)
                                        res = -1;
                                break;
                        case Token.EXTERN:
                                if (parsing_declaration == 0)
                                        res = Token.EXTERN_ALIAS;
                                break;
                        case Token.DEFAULT:
                                if (peek_token () == Token.COLON) {
                                        token ();
                                        res = Token.DEFAULT_COLON;
                                }
                                break;
                        case Token.WHERE:
                                if (!handle_where && !query_parsing)
                                        res = -1;
                                break;
                        case Token.FROM:
                                //
                                // A query expression is any expression that starts with `from identifier'
                                // followed by any token except ; , =
                                // 
                                if (!query_parsing) {
                                        if (lambda_arguments_parsing) {
                                                res = -1;
                                                break;
                                        }

                                        PushPosition ();
                                        // HACK: to disable generics micro-parser, because PushPosition does not
                                        // store identifiers array
                                        parsing_generic_less_than = 1;
                                        switch (xtoken ()) {
                                        case Token.IDENTIFIER:
                                        case Token.INT:
                                        case Token.BOOL:
                                        case Token.BYTE:
                                        case Token.CHAR:
                                        case Token.DECIMAL:
                                        case Token.FLOAT:
                                        case Token.LONG:
                                        case Token.OBJECT:
                                        case Token.STRING:
                                        case Token.UINT:
                                        case Token.ULONG:
                                                next_token = xtoken ();
                                                if (next_token == Token.SEMICOLON || next_token == Token.COMMA || next_token == Token.EQUALS)
                                                        goto default;
                                                
                                                res = Token.FROM_FIRST;
                                                query_parsing = true;
                                                if (context.Settings.Version <= LanguageVersion.ISO_2)
                                                        Report.FeatureIsNotAvailable (context, Location, "query expressions");
                                                break;
                                        case Token.VOID:
                                                Expression.Error_VoidInvalidInTheContext (Location, Report);
                                                break;
                                        default:
                                                PopPosition ();
                                                // HACK: A token is not a keyword so we need to restore identifiers buffer
                                                // which has been overwritten before we grabbed the identifier
                                                id_builder [0] = 'f'; id_builder [1] = 'r'; id_builder [2] = 'o'; id_builder [3] = 'm';
                                                return -1;
                                        }
                                        PopPosition ();
                                }
                                break;
                        case Token.JOIN:
                        case Token.ON:
                        case Token.EQUALS:
                        case Token.SELECT:
                        case Token.GROUP:
                        case Token.BY:
                        case Token.LET:
                        case Token.ORDERBY:
                        case Token.ASCENDING:
                        case Token.DESCENDING:
                        case Token.INTO:
                                if (!query_parsing)
                                        res = -1;
                                break;
                                
                        case Token.USING:
                        case Token.NAMESPACE:
                                // TODO: some explanation needed
                                check_incorrect_doc_comment ();
                                break;
                                
                        case Token.PARTIAL:
                                if (parsing_block > 0) {
                                        res = -1;
                                        break;
                                }

                                // Save current position and parse next token.
                                PushPosition ();

                                next_token = token ();
                                bool ok = (next_token == Token.CLASS) ||
                                        (next_token == Token.STRUCT) ||
                                        (next_token == Token.INTERFACE) ||
                                        (next_token == Token.VOID);

                                PopPosition ();

                                if (ok) {
                                        if (next_token == Token.VOID) {
                                                if (context.Settings.Version <= LanguageVersion.ISO_2)
                                                        Report.FeatureIsNotAvailable (context, Location, "partial methods");
                                        } else if (context.Settings.Version == LanguageVersion.ISO_1)
                                                Report.FeatureIsNotAvailable (context, Location, "partial types");

                                        return res;
                                }

                                if (next_token < Token.LAST_KEYWORD) {
                                        Report.Error (267, Location,
                                                "The `partial' modifier can be used only immediately before `class', `struct', `interface', or `void' keyword");
                                        return token ();
                                }                                       

                                res = -1;
                                break;

                        case Token.ASYNC:
                                if (parsing_modifiers) {
                                        //
                                        // Skip attributes section or constructor called async
                                        //
                                        if (parsing_attribute_section || peek_token () == Token.OPEN_PARENS) {
                                                res = -1;
                                        } else {
                                                // async is keyword
                                        }
                                } else if (parsing_block > 0) {
                                        switch (peek_token ()) {
                                        case Token.DELEGATE:
                                        case Token.OPEN_PARENS_LAMBDA:
                                                // async is keyword
                                                break;
                                        case Token.IDENTIFIER:
                                                PushPosition ();
                                                xtoken ();
                                                if (xtoken () != Token.ARROW)
                                                        goto default;

                                                PopPosition ();
                                                break;
                                        default:
                                                // peek_token could overwrite id_buffer
                                                id_builder [0] = 'a'; id_builder [1] = 's'; id_builder [2] = 'y'; id_builder [3] = 'n'; id_builder [4] = 'c';
                                                res = -1;
                                                break;
                                        }
                                } else {
                                        res = -1;
                                }

                                if (res == Token.ASYNC && context.Settings.Version <= LanguageVersion.V_4) {
                                        Report.FeatureIsNotAvailable (context, Location, "asynchronous functions");
                                }
                                
                                break;

                        case Token.AWAIT:
                                if (parsing_block == 0)
                                        res = -1;

                                break;
                        }


                        return res;
                }

                static PreprocessorDirective GetPreprocessorDirective (char[] id, int id_len)
                {
                        //
                        // Keywords are stored in an array of arrays grouped by their
                        // length and then by the first character
                        //
                        if (id_len >= keywords_preprocessor.Length || keywords_preprocessor[id_len] == null)
                                return PreprocessorDirective.Invalid;

                        int first_index = id[0] - '_';
                        if (first_index > 'z' - '_')
                                return PreprocessorDirective.Invalid;

                        var kwe = keywords_preprocessor[id_len][first_index];
                        if (kwe == null)
                                return PreprocessorDirective.Invalid;

                        PreprocessorDirective res = PreprocessorDirective.Invalid;
                        do {
                                res = kwe.Token;
                                for (int i = 1; i < id_len; ++i) {
                                        if (id[i] != kwe.Value[i]) {
                                                res = 0;
                                                kwe = kwe.Next;
                                                break;
                                        }
                                }
                        } while (res == PreprocessorDirective.Invalid && kwe != null);

                        return res;
                }

                public Location Location {
                        get {
                                return new Location (current_source, ref_line, col);
                        }
                }

                static bool is_identifier_start_character (int c)
                {
                        return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_' || Char.IsLetter ((char)c);
                }

                static bool is_identifier_part_character (char c)
                {
                        if (c >= 'a' && c <= 'z')
                                return true;

                        if (c >= 'A' && c <= 'Z')
                                return true;

                        if (c == '_' || (c >= '0' && c <= '9'))
                                return true;

                        if (c < 0x80)
                                return false;

                        return Char.IsLetter (c) || Char.GetUnicodeCategory (c) == UnicodeCategory.ConnectorPunctuation;
                }

                public static bool IsKeyword (string s)
                {
                        return keyword_strings.Contains (s);
                }

                //
                // Open parens micro parser. Detects both lambda and cast ambiguity.
                //      
                int TokenizeOpenParens ()
                {
                        int ptoken;
                        current_token = -1;

                        int bracket_level = 0;
                        bool is_type = false;
                        bool can_be_type = false;
                        
                        while (true) {
                                ptoken = current_token;
                                token ();

                                switch (current_token) {
                                case Token.CLOSE_PARENS:
                                        token ();
                                        
                                        //
                                        // Expression inside parens is lambda, (int i) => 
                                        //
                                        if (current_token == Token.ARROW)
                                                return Token.OPEN_PARENS_LAMBDA;

                                        //
                                        // Expression inside parens is single type, (int[])
                                        //
                                        if (is_type)
                                                return Token.OPEN_PARENS_CAST;

                                        //
                                        // Expression is possible cast, look at next token, (T)null
                                        //
                                        if (can_be_type) {
                                                switch (current_token) {
                                                case Token.OPEN_PARENS:
                                                case Token.BANG:
                                                case Token.TILDE:
                                                case Token.IDENTIFIER:
                                                case Token.LITERAL:
                                                case Token.BASE:
                                                case Token.CHECKED:
                                                case Token.DELEGATE:
                                                case Token.FALSE:
                                                case Token.FIXED:
                                                case Token.NEW:
                                                case Token.NULL:
                                                case Token.SIZEOF:
                                                case Token.THIS:
                                                case Token.THROW:
                                                case Token.TRUE:
                                                case Token.TYPEOF:
                                                case Token.UNCHECKED:
                                                case Token.UNSAFE:
                                                case Token.DEFAULT:
                                                case Token.AWAIT:

                                                //
                                                // These can be part of a member access
                                                //
                                                case Token.INT:
                                                case Token.UINT:
                                                case Token.SHORT:
                                                case Token.USHORT:
                                                case Token.LONG:
                                                case Token.ULONG:
                                                case Token.DOUBLE:
                                                case Token.FLOAT:
                                                case Token.CHAR:
                                                case Token.BYTE:
                                                case Token.DECIMAL:
                                                case Token.BOOL:
                                                        return Token.OPEN_PARENS_CAST;
                                                }
                                        }
                                        return Token.OPEN_PARENS;
                                        
                                case Token.DOT:
                                case Token.DOUBLE_COLON:
                                        if (ptoken != Token.IDENTIFIER && ptoken != Token.OP_GENERICS_GT)
                                                goto default;

                                        continue;

                                case Token.IDENTIFIER:
                                        switch (ptoken) {
                                        case Token.DOT:
                                                if (bracket_level == 0) {
                                                        is_type = false;
                                                        can_be_type = true;
                                                }

                                                continue;
                                        case Token.OP_GENERICS_LT:
                                        case Token.COMMA:
                                        case Token.DOUBLE_COLON:
                                        case -1:
                                                if (bracket_level == 0)
                                                        can_be_type = true;
                                                continue;
                                        default:
                                                can_be_type = is_type = false;
                                                continue;
                                        }

                                case Token.OBJECT:
                                case Token.STRING:
                                case Token.BOOL:
                                case Token.DECIMAL:
                                case Token.FLOAT:
                                case Token.DOUBLE:
                                case Token.SBYTE:
                                case Token.BYTE:
                                case Token.SHORT:
                                case Token.USHORT:
                                case Token.INT:
                                case Token.UINT:
                                case Token.LONG:
                                case Token.ULONG:
                                case Token.CHAR:
                                case Token.VOID:
                                        if (bracket_level == 0)
                                                is_type = true;
                                        continue;

                                case Token.COMMA:
                                        if (bracket_level == 0) {
                                                bracket_level = 100;
                                                can_be_type = is_type = false;
                                        }
                                        continue;

                                case Token.OP_GENERICS_LT:
                                case Token.OPEN_BRACKET:
                                        if (bracket_level++ == 0)
                                                is_type = true;
                                        continue;

                                case Token.OP_GENERICS_GT:
                                case Token.CLOSE_BRACKET:
                                        --bracket_level;
                                        continue;

                                case Token.INTERR_NULLABLE:
                                case Token.STAR:
                                        if (bracket_level == 0)
                                                is_type = true;
                                        continue;

                                case Token.REF:
                                case Token.OUT:
                                        can_be_type = is_type = false;
                                        continue;

                                default:
                                        return Token.OPEN_PARENS;
                                }
                        }
                }

                public static bool IsValidIdentifier (string s)
                {
                        if (s == null || s.Length == 0)
                                return false;

                        if (!is_identifier_start_character (s [0]))
                                return false;
                        
                        for (int i = 1; i < s.Length; i ++)
                                if (! is_identifier_part_character (s [i]))
                                        return false;
                        
                        return true;
                }

                bool parse_less_than ()
                {
                start:
                        int the_token = token ();
                        if (the_token == Token.OPEN_BRACKET) {
                                while (true) {
                                        the_token = token ();
                                        if (the_token == Token.EOF)
                                                return true;

                                        if (the_token == Token.CLOSE_BRACKET)
                                                break;
                                }
                                the_token = token ();
                        } else if (the_token == Token.IN || the_token == Token.OUT) {
                                the_token = token ();
                        }
                        switch (the_token) {
                        case Token.IDENTIFIER:
                        case Token.OBJECT:
                        case Token.STRING:
                        case Token.BOOL:
                        case Token.DECIMAL:
                        case Token.FLOAT:
                        case Token.DOUBLE:
                        case Token.SBYTE:
                        case Token.BYTE:
                        case Token.SHORT:
                        case Token.USHORT:
                        case Token.INT:
                        case Token.UINT:
                        case Token.LONG:
                        case Token.ULONG:
                        case Token.CHAR:
                        case Token.VOID:
                                break;
                        case Token.OP_GENERICS_GT:
                        case Token.IN:
                        case Token.OUT:
                                return true;

                        default:
                                return false;
                        }
                again:
                        the_token = token ();

                        if (the_token == Token.OP_GENERICS_GT)
                                return true;
                        else if (the_token == Token.COMMA || the_token == Token.DOT || the_token == Token.DOUBLE_COLON)
                                goto start;
                        else if (the_token == Token.INTERR_NULLABLE || the_token == Token.STAR)
                                goto again;
                        else if (the_token == Token.OP_GENERICS_LT) {
                                if (!parse_less_than ())
                                        return false;
                                goto again;
                        } else if (the_token == Token.OPEN_BRACKET) {
                        rank_specifiers:
                                the_token = token ();
                                if (the_token == Token.CLOSE_BRACKET)
                                        goto again;
                                else if (the_token == Token.COMMA)
                                        goto rank_specifiers;
                                return false;
                        }

                        return false;
                }

                bool parse_generic_dimension (out int dimension)
                {
                        dimension = 1;

                again:
                        int the_token = token ();
                        if (the_token == Token.OP_GENERICS_GT)
                                return true;
                        else if (the_token == Token.COMMA) {
                                dimension++;
                                goto again;
                        }

                        return false;
                }
                
                public int peek_token ()
                {
                        int the_token;

                        PushPosition ();
                        the_token = token ();
                        PopPosition ();
                        
                        return the_token;
                }
                                        
                //
                // Tonizes `?' using custom disambiguous rules to return one
                // of following tokens: INTERR_NULLABLE, OP_COALESCING, INTERR
                //
                // Tricky expression look like:
                //
                // Foo ? a = x ? b : c;
                //
                int TokenizePossibleNullableType ()
                {
                        if (parsing_block == 0 || parsing_type > 0)
                                return Token.INTERR_NULLABLE;

                        int d = peek_char ();
                        if (d == '?') {
                                get_char ();
                                return Token.OP_COALESCING;
                        }

                        switch (current_token) {
                        case Token.CLOSE_PARENS:
                        case Token.TRUE:
                        case Token.FALSE:
                        case Token.NULL:
                        case Token.LITERAL:
                                return Token.INTERR;
                        }

                        if (d != ' ') {
                                if (d == ',' || d == ';' || d == '>')
                                        return Token.INTERR_NULLABLE;
                                if (d == '*' || (d >= '0' && d <= '9'))
                                        return Token.INTERR;
                        }

                        PushPosition ();
                        current_token = Token.NONE;
                        int next_token;
                        switch (xtoken ()) {
                        case Token.LITERAL:
                        case Token.TRUE:
                        case Token.FALSE:
                        case Token.NULL:
                        case Token.THIS:
                        case Token.NEW:
                                next_token = Token.INTERR;
                                break;
                                
                        case Token.SEMICOLON:
                        case Token.COMMA:
                        case Token.CLOSE_PARENS:
                        case Token.OPEN_BRACKET:
                        case Token.OP_GENERICS_GT:
                        case Token.INTERR:
                                next_token = Token.INTERR_NULLABLE;
                                break;
                                
                        default:
                                next_token = -1;
                                break;
                        }

                        if (next_token == -1) {
                                switch (xtoken ()) {
                                case Token.COMMA:
                                case Token.SEMICOLON:
                                case Token.OPEN_BRACE:
                                case Token.CLOSE_PARENS:
                                case Token.IN:
                                        next_token = Token.INTERR_NULLABLE;
                                        break;
                                        
                                case Token.COLON:
                                        next_token = Token.INTERR;
                                        break;                                                  
                                        
                                default:
                                        int ntoken;
                                        int interrs = 1;
                                        int colons = 0;
                                        int braces = 0;
                                        //
                                        // All shorcuts failed, do it hard way
                                        //
                                        while ((ntoken = xtoken ()) != Token.EOF) {
                                                if (ntoken == Token.OPEN_BRACE) {
                                                        ++braces;
                                                        continue;
                                                }

                                                if (ntoken == Token.CLOSE_BRACE) {
                                                        --braces;
                                                        continue;
                                                }

                                                if (braces != 0)
                                                        continue;

                                                if (ntoken == Token.SEMICOLON)
                                                        break;
                                                
                                                if (ntoken == Token.COLON) {
                                                        if (++colons == interrs)
                                                                break;
                                                        continue;
                                                }
                                                
                                                if (ntoken == Token.INTERR) {
                                                        ++interrs;
                                                        continue;
                                                }
                                        }
                                        
                                        next_token = colons != interrs && braces == 0 ? Token.INTERR_NULLABLE : Token.INTERR;
                                        break;
                                }
                        }
                        
                        PopPosition ();
                        return next_token;
                }

                bool decimal_digits (int c)
                {
                        int d;
                        bool seen_digits = false;
                        
                        if (c != -1){
                                if (number_pos == MaxNumberLength)
                                        Error_NumericConstantTooLong ();
                                number_builder [number_pos++] = (char) c;
                        }
                        
                        //
                        // We use peek_char2, because decimal_digits needs to do a 
                        // 2-character look-ahead (5.ToString for example).
                        //
                        while ((d = peek_char2 ()) != -1){
                                if (d >= '0' && d <= '9'){
                                        if (number_pos == MaxNumberLength)
                                                Error_NumericConstantTooLong ();
                                        number_builder [number_pos++] = (char) d;
                                        get_char ();
                                        seen_digits = true;
                                } else
                                        break;
                        }
                        
                        return seen_digits;
                }

                static bool is_hex (int e)
                {
                        return (e >= '0' && e <= '9') || (e >= 'A' && e <= 'F') || (e >= 'a' && e <= 'f');
                }

                static TypeCode real_type_suffix (int c)
                {
                        switch (c){
                        case 'F': case 'f':
                                return TypeCode.Single;
                        case 'D': case 'd':
                                return TypeCode.Double;
                        case 'M': case 'm':
                                return TypeCode.Decimal;
                        default:
                                return TypeCode.Empty;
                        }
                }

                ILiteralConstant integer_type_suffix (ulong ul, int c, Location loc)
                {
                        bool is_unsigned = false;
                        bool is_long = false;

                        if (c != -1){
                                bool scanning = true;
                                do {
                                        switch (c){
                                        case 'U': case 'u':
                                                if (is_unsigned)
                                                        scanning = false;
                                                is_unsigned = true;
                                                get_char ();
                                                break;

                                        case 'l':
                                                if (!is_unsigned){
                                                        //
                                                        // if we have not seen anything in between
                                                        // report this error
                                                        //
                                                        Report.Warning (78, 4, Location, "The 'l' suffix is easily confused with the digit '1' (use 'L' for clarity)");
                                                }

                                                goto case 'L';

                                        case 'L': 
                                                if (is_long)
                                                        scanning = false;
                                                is_long = true;
                                                get_char ();
                                                break;
                                                
                                        default:
                                                scanning = false;
                                                break;
                                        }
                                        c = peek_char ();
                                } while (scanning);
                        }

                        if (is_long && is_unsigned){
                                return new ULongLiteral (context.BuiltinTypes, ul, loc);
                        }
                        
                        if (is_unsigned){
                                // uint if possible, or ulong else.

                                if ((ul & 0xffffffff00000000) == 0)
                                        return new UIntLiteral (context.BuiltinTypes, (uint) ul, loc);
                                else
                                        return new ULongLiteral (context.BuiltinTypes, ul, loc);
                        } else if (is_long){
                                // long if possible, ulong otherwise
                                if ((ul & 0x8000000000000000) != 0)
                                        return new ULongLiteral (context.BuiltinTypes, ul, loc);
                                else
                                        return new LongLiteral (context.BuiltinTypes, (long) ul, loc);
                        } else {
                                // int, uint, long or ulong in that order
                                if ((ul & 0xffffffff00000000) == 0){
                                        uint ui = (uint) ul;
                                        
                                        if ((ui & 0x80000000) != 0)
                                                return new UIntLiteral (context.BuiltinTypes, ui, loc);
                                        else
                                                return new IntLiteral (context.BuiltinTypes, (int) ui, loc);
                                } else {
                                        if ((ul & 0x8000000000000000) != 0)
                                                return new ULongLiteral (context.BuiltinTypes, ul, loc);
                                        else
                                                return new LongLiteral (context.BuiltinTypes, (long) ul, loc);
                                }
                        }
                }
                                
                //
                // given `c' as the next char in the input decide whether
                // we need to convert to a special type, and then choose
                // the best representation for the integer
                //
                ILiteralConstant adjust_int (int c, Location loc)
                {
                        try {
                                if (number_pos > 9){
                                        ulong ul = (uint) (number_builder [0] - '0');

                                        for (int i = 1; i < number_pos; i++){
                                                ul = checked ((ul * 10) + ((uint)(number_builder [i] - '0')));
                                        }

                                        return integer_type_suffix (ul, c, loc);
                                } else {
                                        uint ui = (uint) (number_builder [0] - '0');

                                        for (int i = 1; i < number_pos; i++){
                                                ui = checked ((ui * 10) + ((uint)(number_builder [i] - '0')));
                                        }

                                        return integer_type_suffix (ui, c, loc);
                                }
                        } catch (OverflowException) {
                                Error_NumericConstantTooLong ();
                                return new IntLiteral (context.BuiltinTypes, 0, loc);
                        }
                        catch (FormatException) {
                                Report.Error (1013, Location, "Invalid number");
                                return new IntLiteral (context.BuiltinTypes, 0, loc);
                        }
                }
                
                ILiteralConstant adjust_real (TypeCode t, Location loc)
                {
                        string s = new string (number_builder, 0, number_pos);
                        const string error_details = "Floating-point constant is outside the range of type `{0}'";

                        switch (t){
                        case TypeCode.Decimal:
                                try {
                                        return new DecimalLiteral (context.BuiltinTypes, decimal.Parse (s, styles, csharp_format_info), loc);
                                } catch (OverflowException) {
                                        Report.Error (594, Location, error_details, "decimal");
                                        return new DecimalLiteral (context.BuiltinTypes, 0, loc);
                                }
                        case TypeCode.Single:
                                try {
                                        return new FloatLiteral (context.BuiltinTypes, float.Parse (s, styles, csharp_format_info), loc);
                                } catch (OverflowException) {
                                        Report.Error (594, Location, error_details, "float");
                                        return new FloatLiteral (context.BuiltinTypes, 0, loc);
                                }
                        default:
                                try {
                                        return new DoubleLiteral (context.BuiltinTypes, double.Parse (s, styles, csharp_format_info), loc);
                                } catch (OverflowException) {
                                        Report.Error (594, loc, error_details, "double");
                                        return new DoubleLiteral (context.BuiltinTypes, 0, loc);
                                }
                        }
                }

                ILiteralConstant handle_hex (Location loc)
                {
                        int d;
                        ulong ul;
                        
                        get_char ();
                        while ((d = peek_char ()) != -1){
                                if (is_hex (d)){
                                        number_builder [number_pos++] = (char) d;
                                        get_char ();
                                } else
                                        break;
                        }
                        
                        string s = new String (number_builder, 0, number_pos);

                        try {
                                if (number_pos <= 8)
                                        ul = System.UInt32.Parse (s, NumberStyles.HexNumber);
                                else
                                        ul = System.UInt64.Parse (s, NumberStyles.HexNumber);

                                return integer_type_suffix (ul, peek_char (), loc);
                        } catch (OverflowException){
                                Error_NumericConstantTooLong ();
                                return new IntLiteral (context.BuiltinTypes, 0, loc);
                        }
                        catch (FormatException) {
                                Report.Error (1013, Location, "Invalid number");
                                return new IntLiteral (context.BuiltinTypes, 0, loc);
                        }
                }

                //
                // Invoked if we know we have .digits or digits
                //
                int is_number (int c)
                {
                        ILiteralConstant res;

#if FULL_AST
                        int read_start = reader.Position - 1;
                        if (c == '.') {
                                //
                                // Caller did peek_char
                                //
                                --read_start;
                        }
#endif
                        number_pos = 0;
                        var loc = Location;

                        if (c >= '0' && c <= '9'){
                                if (c == '0'){
                                        int peek = peek_char ();

                                        if (peek == 'x' || peek == 'X') {
                                                val = res = handle_hex (loc);
#if FULL_AST
                                                res.ParsedValue = reader.ReadChars (read_start, reader.Position - 1);
#endif

                                                return Token.LITERAL;
                                        }
                                }
                                decimal_digits (c);
                                c = get_char ();
                        }

                        //
                        // We need to handle the case of
                        // "1.1" vs "1.string" (LITERAL_FLOAT vs NUMBER DOT IDENTIFIER)
                        //
                        bool is_real = false;
                        if (c == '.'){
                                if (decimal_digits ('.')){
                                        is_real = true;
                                        c = get_char ();
                                } else {
                                        putback ('.');
                                        number_pos--;
                                        val = res = adjust_int (-1, loc);

#if FULL_AST
                                        res.ParsedValue = reader.ReadChars (read_start, reader.Position - 1);
#endif
                                        return Token.LITERAL;
                                }
                        }
                        
                        if (c == 'e' || c == 'E'){
                                is_real = true;
                                if (number_pos == MaxNumberLength)
                                        Error_NumericConstantTooLong ();
                                number_builder [number_pos++] = (char) c;
                                c = get_char ();
                                
                                if (c == '+'){
                                        if (number_pos == MaxNumberLength)
                                                Error_NumericConstantTooLong ();
                                        number_builder [number_pos++] = '+';
                                        c = -1;
                                } else if (c == '-') {
                                        if (number_pos == MaxNumberLength)
                                                Error_NumericConstantTooLong ();
                                        number_builder [number_pos++] = '-';
                                        c = -1;
                                } else {
                                        if (number_pos == MaxNumberLength)
                                                Error_NumericConstantTooLong ();
                                        number_builder [number_pos++] = '+';
                                }
                                        
                                decimal_digits (c);
                                c = get_char ();
                        }

                        var type = real_type_suffix (c);
                        if (type == TypeCode.Empty && !is_real) {
                                putback (c);
                                res = adjust_int (c, loc);
                        } else {
                                is_real = true;

                                if (type == TypeCode.Empty) {
                                        putback (c);
                                }

                                res = adjust_real (type, loc);
                        }

                        val = res;

#if FULL_AST
                        var chars = reader.ReadChars (read_start, reader.Position - (type == TypeCode.Empty && c > 0 ? 1 : 0));
                        if (chars[chars.Length - 1] == '\r')
                                Array.Resize (ref chars, chars.Length - 1);
                        res.ParsedValue = chars;
#endif

                        return Token.LITERAL;
                }

                //
                // Accepts exactly count (4 or 8) hex, no more no less
                //
                int getHex (int count, out int surrogate, out bool error)
                {
                        int i;
                        int total = 0;
                        int c;
                        int top = count != -1 ? count : 4;
                        
                        get_char ();
                        error = false;
                        surrogate = 0;
                        for (i = 0; i < top; i++){
                                c = get_char ();

                                if (c >= '0' && c <= '9')
                                        c = (int) c - (int) '0';
                                else if (c >= 'A' && c <= 'F')
                                        c = (int) c - (int) 'A' + 10;
                                else if (c >= 'a' && c <= 'f')
                                        c = (int) c - (int) 'a' + 10;
                                else {
                                        error = true;
                                        return 0;
                                }
                                
                                total = (total * 16) + c;
                                if (count == -1){
                                        int p = peek_char ();
                                        if (p == -1)
                                                break;
                                        if (!is_hex ((char)p))
                                                break;
                                }
                        }

                        if (top == 8) {
                                if (total > 0x0010FFFF) {
                                        error = true;
                                        return 0;
                                }

                                if (total >= 0x00010000) {
                                        surrogate = ((total - 0x00010000) % 0x0400 + 0xDC00);                                   
                                        total = ((total - 0x00010000) / 0x0400 + 0xD800);
                                }
                        }

                        return total;
                }

                int escape (int c, out int surrogate)
                {
                        bool error;
                        int d;
                        int v;

                        d = peek_char ();
                        if (c != '\\') {
                                surrogate = 0;
                                return c;
                        }
                        
                        switch (d){
                        case 'a':
                                v = '\a'; break;
                        case 'b':
                                v = '\b'; break;
                        case 'n':
                                v = '\n'; break;
                        case 't':
                                v = '\t'; break;
                        case 'v':
                                v = '\v'; break;
                        case 'r':
                                v = '\r'; break;
                        case '\\':
                                v = '\\'; break;
                        case 'f':
                                v = '\f'; break;
                        case '0':
                                v = 0; break;
                        case '"':
                                v = '"'; break;
                        case '\'':
                                v = '\''; break;
                        case 'x':
                                v = getHex (-1, out surrogate, out error);
                                if (error)
                                        goto default;
                                return v;
                        case 'u':
                        case 'U':
                                return EscapeUnicode (d, out surrogate);
                        default:
                                surrogate = 0;
                                Report.Error (1009, Location, "Unrecognized escape sequence `\\{0}'", ((char)d).ToString ());
                                return d;
                        }

                        get_char ();
                        surrogate = 0;
                        return v;
                }

                int EscapeUnicode (int ch, out int surrogate)
                {
                        bool error;
                        if (ch == 'U') {
                                ch = getHex (8, out surrogate, out error);
                        } else {
                                ch = getHex (4, out surrogate, out error);
                        }

                        if (error)
                                Report.Error (1009, Location, "Unrecognized escape sequence");

                        return ch;
                }

                int get_char ()
                {
                        int x;
                        if (putback_char != -1) {
                                x = putback_char;
                                putback_char = -1;
                        } else {
                                x = reader.Read ();
                        }
                        
                        if (x == '\r') {
                                if (peek_char () == '\n') {
                                        putback_char = -1;
                                }

                                x = '\n';
                                advance_line ();
                        } else if (x == '\n') {
                                advance_line ();
                        } else {
                                col++;
                        }
                        return x;
                }

                void advance_line ()
                {
                        line++;
                        ref_line++;
                        previous_col = col;
                        col = 0;
                }

                int peek_char ()
                {
                        if (putback_char == -1)
                                putback_char = reader.Read ();
                        return putback_char;
                }

                int peek_char2 ()
                {
                        if (putback_char != -1)
                                return putback_char;
                        return reader.Peek ();
                }
                
                public void putback (int c)
                {
                        if (putback_char != -1) {
                                throw new InternalErrorException (string.Format ("Secondary putback [{0}] putting back [{1}] is not allowed", (char)putback_char, (char) c), Location);
                        }

                        if (c == '\n' || col == 0) {
                                // It won't happen though.
                                line--;
                                ref_line--;
                                col = previous_col;
                        }
                        else
                                col--;
                        putback_char = c;
                }

                public bool advance ()
                {
                        return peek_char () != -1 || CompleteOnEOF;
                }

                public Object Value {
                        get {
                                return val;
                        }
                }

                public Object value ()
                {
                        return val;
                }

                public int token ()
                {
                        current_token = xtoken ();
                        return current_token;
                }

                int TokenizePreprocessorIdentifier (out int c)
                {
                        // skip over white space
                        do {
                                c = get_char ();
                        } while (c == ' ' || c == '\t');


                        int pos = 0;
                        while (c != -1 && c >= 'a' && c <= 'z') {
                                id_builder[pos++] = (char) c;
                                c = get_char ();
                                if (c == '\\') {
                                        int peek = peek_char ();
                                        if (peek == 'U' || peek == 'u') {
                                                int surrogate;
                                                c = EscapeUnicode (c, out surrogate);
                                                if (surrogate != 0) {
                                                        if (is_identifier_part_character ((char) c)) {
                                                                id_builder[pos++] = (char) c;
                                                        }
                                                        c = surrogate;
                                                }
                                        }
                                }
                        }

                        return pos;
                }

                PreprocessorDirective get_cmd_arg (out string arg)
                {
                        int c;          

                        tokens_seen = false;
                        arg = "";

                        var cmd = GetPreprocessorDirective (id_builder, TokenizePreprocessorIdentifier (out c));

                        if ((cmd & PreprocessorDirective.CustomArgumentsParsing) != 0)
                                return cmd;

                        // skip over white space
                        while (c == ' ' || c == '\t')
                                c = get_char ();

                        int has_identifier_argument = (int)(cmd & PreprocessorDirective.RequiresArgument);
                        int pos = 0;

                        while (c != -1 && c != '\n') {
                                if (c == '\\' && has_identifier_argument >= 0) {
                                        if (has_identifier_argument != 0) {
                                                has_identifier_argument = 1;

                                                int peek = peek_char ();
                                                if (peek == 'U' || peek == 'u') {
                                                        int surrogate;
                                                        c = EscapeUnicode (c, out surrogate);
                                                        if (surrogate != 0) {
                                                                if (is_identifier_part_character ((char) c)) {
                                                                        if (pos == value_builder.Length)
                                                                                Array.Resize (ref value_builder, pos * 2);

                                                                        value_builder[pos++] = (char) c;
                                                                }
                                                                c = surrogate;
                                                        }
                                                }
                                        } else {
                                                has_identifier_argument = -1;
                                        }
                                } else if (c == '/' && peek_char () == '/') {
                                        //
                                        // Eat single-line comments
                                        //
                                        get_char ();
                                        do {
                                                c = get_char ();
                                        } while (c != -1 && c != '\n');

                                        break;
                                }

                                if (pos == value_builder.Length)
                                        Array.Resize (ref value_builder, pos * 2);

                                value_builder[pos++] = (char) c;
                                c = get_char ();
                        }

                        if (pos != 0) {
                                if (pos > MaxIdentifierLength)
                                        arg = new string (value_builder, 0, pos);
                                else
                                        arg = InternIdentifier (value_builder, pos);

                                // Eat any trailing whitespaces
                                arg = arg.Trim (simple_whitespaces);
                        }

                        return cmd;
                }

                //
                // Handles the #line directive
                //
                bool PreProcessLine ()
                {
                        Location loc = Location;

                        int c;

                        int length = TokenizePreprocessorIdentifier (out c);
                        if (length == line_default.Length) {
                                if (!IsTokenIdentifierEqual (line_default))
                                        return false;

                                current_source = source_file.SourceFile;
                                if (!hidden_block_start.IsNull) {
                                        current_source.RegisterHiddenScope (hidden_block_start, loc);
                                        hidden_block_start = Location.Null;
                                }

                                ref_line = line;
                                return true;
                        }

                        if (length == line_hidden.Length) {
                                if (!IsTokenIdentifierEqual (line_hidden))
                                        return false;

                                if (hidden_block_start.IsNull)
                                        hidden_block_start = loc;

                                return true;
                        }

                        if (length != 0 || c < '0' || c > '9') {
                                //
                                // Eat any remaining characters to continue parsing on next line
                                //
                                while (c != -1 && c != '\n') {
                                        c = get_char ();
                                }

                                return false;
                        }

                        int new_line = TokenizeNumber (c);
                        if (new_line < 1) {
                                //
                                // Eat any remaining characters to continue parsing on next line
                                //
                                while (c != -1 && c != '\n') {
                                        c = get_char ();
                                }

                                return new_line != 0;
                        }

                        c = get_char ();
                        if (c == ' ') {
                                // skip over white space
                                do {
                                        c = get_char ();
                                } while (c == ' ' || c == '\t');
                        } else if (c == '"') {
                                c = 0;
                        }

                        if (c != '\n' && c != '/' && c != '"') {
                                //
                                // Eat any remaining characters to continue parsing on next line
                                //
                                while (c != -1 && c != '\n') {
                                        c = get_char ();
                                }

                                Report.Error (1578, loc, "Filename, single-line comment or end-of-line expected");
                                return true;
                        }

                        string new_file_name = null;
                        if (c == '"') {
                                new_file_name = TokenizeFileName (ref c);

                                // skip over white space
                                while (c == ' ' || c == '\t') {
                                        c = get_char ();
                                }
                        }

                        if (c == '\n') {
                        } else if (c == '/') {
                                ReadSingleLineComment ();
                        } else {
                                //
                                // Eat any remaining characters to continue parsing on next line
                                //
                                while (c != -1 && c != '\n') {
                                        c = get_char ();
                                }

                                Error_EndLineExpected ();
                                return true;
                        }

                        if (new_file_name != null) {
                                current_source = context.LookupFile (source_file, new_file_name);
                                source_file.AddIncludeFile (current_source);
                        }

                        if (!hidden_block_start.IsNull) {
                                current_source.RegisterHiddenScope (hidden_block_start, loc);
                                hidden_block_start = Location.Null;
                        }

                        ref_line = new_line;
                        return true;
                }

                //
                // Handles #define and #undef
                //
                void PreProcessDefinition (bool is_define, string ident, bool caller_is_taking)
                {
                        if (ident.Length == 0 || ident == "true" || ident == "false"){
                                Report.Error (1001, Location, "Missing identifier to pre-processor directive");
                                return;
                        }

                        if (ident.IndexOfAny (simple_whitespaces) != -1){
                                Error_EndLineExpected ();
                                return;
                        }

                        if (!is_identifier_start_character (ident [0]))
                                Report.Error (1001, Location, "Identifier expected: {0}", ident);
                        
                        foreach (char c in ident.Substring (1)){
                                if (!is_identifier_part_character (c)){
                                        Report.Error (1001, Location, "Identifier expected: {0}",  ident);
                                        return;
                                }
                        }

                        if (!caller_is_taking)
                                return;

                        if (is_define) {
                                //
                                // #define ident
                                //
                                if (context.Settings.IsConditionalSymbolDefined (ident))
                                        return;

                                source_file.AddDefine (ident);
                        } else {
                                //
                                // #undef ident
                                //
                                source_file.AddUndefine (ident);
                        }
                }

                byte read_hex (out bool error)
                {
                        int total;
                        int c = get_char ();

                        if ((c >= '0') && (c <= '9'))
                                total = (int) c - (int) '0';
                        else if ((c >= 'A') && (c <= 'F'))
                                total = (int) c - (int) 'A' + 10;
                        else if ((c >= 'a') && (c <= 'f'))
                                total = (int) c - (int) 'a' + 10;
                        else {
                                error = true;
                                return 0;
                        }

                        total *= 16;
                        c = get_char ();

                        if ((c >= '0') && (c <= '9'))
                                total += (int) c - (int) '0';
                        else if ((c >= 'A') && (c <= 'F'))
                                total += (int) c - (int) 'A' + 10;
                        else if ((c >= 'a') && (c <= 'f'))
                                total += (int) c - (int) 'a' + 10;
                        else {
                                error = true;
                                return 0;
                        }

                        error = false;
                        return (byte) total;
                }

                //
                // Parses #pragma checksum
                //
                bool ParsePragmaChecksum ()
                {
                        //
                        // The syntax is ` "foo.txt" "{guid}" "hash"'
                        //
                        // guid is predefined hash algorithm guid {406ea660-64cf-4c82-b6f0-42d48172a799} for md5
                        //
                        int c = get_char ();

                        if (c != '"')
                                return false;

                        string file_name = TokenizeFileName (ref c);

                        // TODO: Any white-spaces count
                        if (c != ' ')
                                return false;

                        SourceFile file = context.LookupFile (source_file, file_name);

                        if (get_char () != '"' || get_char () != '{')
                                return false;

                        bool error;
                        byte[] guid_bytes = new byte [16];
                        int i = 0;

                        for (; i < 4; i++) {
                                guid_bytes [i] = read_hex (out error);
                                if (error)
                                        return false;
                        }

                        if (get_char () != '-')
                                return false;

                        for (; i < 10; i++) {
                                guid_bytes [i] = read_hex (out error);
                                if (error)
                                        return false;

                                guid_bytes [i++] = read_hex (out error);
                                if (error)
                                        return false;

                                if (get_char () != '-')
                                        return false;
                        }

                        for (; i < 16; i++) {
                                guid_bytes [i] = read_hex (out error);
                                if (error)
                                        return false;
                        }

                        if (get_char () != '}' || get_char () != '"')
                                return false;

                        // TODO: Any white-spaces count
                        c = get_char ();
                        if (c != ' ')
                                return false;

                        if (get_char () != '"')
                                return false;

                        // Any length of checksum
                        List<byte> checksum_bytes = new List<byte> (16);

                        var checksum_location = Location;
                        c = peek_char ();
                        while (c != '"' && c != -1) {
                                checksum_bytes.Add (read_hex (out error));
                                if (error)
                                        return false;

                                c = peek_char ();
                        }

                        if (c == '/') {
                                ReadSingleLineComment ();
                        } else if (get_char () != '"') {
                                return false;
                        }

                        if (context.Settings.GenerateDebugInfo) {
                                var chsum = checksum_bytes.ToArray ();

                                if (file.HasChecksum) {
                                        if (!ArrayComparer.IsEqual (file.Checksum, chsum)) {
                                                // TODO: Report.SymbolRelatedToPreviousError
                                                Report.Warning (1697, 1, checksum_location, "Different checksum values specified for file `{0}'", file.Name);
                                        }
                                }

                                file.SetChecksum (guid_bytes, chsum);
                                current_source.AutoGenerated = true;
                        }

                        return true;
                }

                bool IsTokenIdentifierEqual (char[] identifier)
                {
                        for (int i = 0; i < identifier.Length; ++i) {
                                if (identifier[i] != id_builder[i])
                                        return false;
                        }

                        return true;
                }

                int TokenizeNumber (int value)
                {
                        number_pos = 0;

                        decimal_digits (value);
                        uint ui = (uint) (number_builder[0] - '0');

                        try {
                                for (int i = 1; i < number_pos; i++) {
                                        ui = checked ((ui * 10) + ((uint) (number_builder[i] - '0')));
                                }

                                return (int) ui;
                        } catch (OverflowException) {
                                Error_NumericConstantTooLong ();
                                return -1;
                        }
                }

                string TokenizeFileName (ref int c)
                {
                        var string_builder = new StringBuilder ();
                        while (c != -1 && c != '\n') {
                                c = get_char ();
                                if (c == '"') {
                                        c = get_char ();
                                        break;
                                }

                                string_builder.Append ((char) c);
                        }

                        if (string_builder.Length == 0) {
                                Report.Warning (1709, 1, Location, "Filename specified for preprocessor directive is empty");
                        }

                
                        return string_builder.ToString ();
                }

                int TokenizePragmaNumber (ref int c)
                {
                        number_pos = 0;

                        int number;

                        if (c >= '0' && c <= '9') {
                                number = TokenizeNumber (c);

                                c = get_char ();

                                // skip over white space
                                while (c == ' ' || c == '\t')
                                        c = get_char ();

                                if (c == ',') {
                                        c = get_char ();
                                }

                                // skip over white space
                                while (c == ' ' || c == '\t')
                                        c = get_char ();
                        } else {
                                number = -1;
                                if (c == '/') {
                                        ReadSingleLineComment ();
                                } else {
                                        Report.Warning (1692, 1, Location, "Invalid number");

                                        // Read everything till the end of the line or file
                                        do {
                                                c = get_char ();
                                        } while (c != -1 && c != '\n');
                                }
                        }

                        return number;
                }

                void ReadSingleLineComment ()
                {
                        if (peek_char () != '/')
                                Report.Warning (1696, 1, Location, "Single-line comment or end-of-line expected");

                        // Read everything till the end of the line or file
                        int c;
                        do {
                                c = get_char ();
                        } while (c != -1 && c != '\n');
                }

                /// <summary>
                /// Handles #pragma directive
                /// </summary>
                void ParsePragmaDirective (string arg)
                {
                        int c;
                        int length = TokenizePreprocessorIdentifier (out c);
                        if (length == pragma_warning.Length && IsTokenIdentifierEqual (pragma_warning)) {
                                length = TokenizePreprocessorIdentifier (out c);

                                //
                                // #pragma warning disable
                                // #pragma warning restore
                                //
                                if (length == pragma_warning_disable.Length) {
                                        bool disable = IsTokenIdentifierEqual (pragma_warning_disable);
                                        if (disable || IsTokenIdentifierEqual (pragma_warning_restore)) {
                                                // skip over white space
                                                while (c == ' ' || c == '\t')
                                                        c = get_char ();

                                                var loc = Location;

                                                if (c == '\n' || c == '/') {
                                                        if (c == '/')
                                                                ReadSingleLineComment ();

                                                        //
                                                        // Disable/Restore all warnings
                                                        //
                                                        if (disable) {
                                                                Report.RegisterWarningRegion (loc).WarningDisable (loc.Row);
                                                        } else {
                                                                Report.RegisterWarningRegion (loc).WarningEnable (loc.Row);
                                                        }
                                                } else {
                                                        //
                                                        // Disable/Restore a warning or group of warnings
                                                        //
                                                        int code;
                                                        do {
                                                                code = TokenizePragmaNumber (ref c);
                                                                if (code > 0) {
                                                                        if (disable) {
                                                                                Report.RegisterWarningRegion (loc).WarningDisable (loc, code, context.Report);
                                                                        } else {
                                                                                Report.RegisterWarningRegion (loc).WarningEnable (loc, code, context);
                                                                        }
                                                                }
                                                        } while (code >= 0 && c != '\n' && c != -1);
                                                }

                                                return;
                                        }
                                }

                                Report.Warning (1634, 1, Location, "Expected disable or restore");

                                // Eat any remaining characters on the line
                                while (c != '\n' && c != -1)
                                        c = get_char ();

                                return;
                        }

                        //
                        // #pragma checksum
                        //
                        if (length == pragma_checksum.Length && IsTokenIdentifierEqual (pragma_checksum)) {
                                if (c != ' ' || !ParsePragmaChecksum ()) {
                                        Report.Warning (1695, 1, Location,
                                                "Invalid #pragma checksum syntax. Expected \"filename\" \"{XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}\" \"XXXX...\"");
                                }

                                return;
                        }

                        Report.Warning (1633, 1, Location, "Unrecognized #pragma directive");
                }

                bool eval_val (string s)
                {
                        if (s == "true")
                                return true;
                        if (s == "false")
                                return false;

                        return source_file.IsConditionalDefined (s);
                }

                bool pp_primary (ref string s)
                {
                        s = s.Trim ();
                        int len = s.Length;

                        if (len > 0){
                                char c = s [0];
                                
                                if (c == '('){
                                        s = s.Substring (1);
                                        bool val = pp_expr (ref s, false);
                                        if (s.Length > 0 && s [0] == ')'){
                                                s = s.Substring (1);
                                                return val;
                                        }
                                        Error_InvalidDirective ();
                                        return false;
                                }
                                
                                if (is_identifier_start_character (c)){
                                        int j = 1;

                                        while (j < len){
                                                c = s [j];
                                                
                                                if (is_identifier_part_character (c)){
                                                        j++;
                                                        continue;
                                                }
                                                bool v = eval_val (s.Substring (0, j));
                                                s = s.Substring (j);
                                                return v;
                                        }
                                        bool vv = eval_val (s);
                                        s = "";
                                        return vv;
                                }
                        }
                        Error_InvalidDirective ();
                        return false;
                }
                
                bool pp_unary (ref string s)
                {
                        s = s.Trim ();
                        int len = s.Length;

                        if (len > 0){
                                if (s [0] == '!'){
                                        if (len > 1 && s [1] == '='){
                                                Error_InvalidDirective ();
                                                return false;
                                        }
                                        s = s.Substring (1);
                                        return ! pp_primary (ref s);
                                } else
                                        return pp_primary (ref s);
                        } else {
                                Error_InvalidDirective ();
                                return false;
                        }
                }
                
                bool pp_eq (ref string s)
                {
                        bool va = pp_unary (ref s);

                        s = s.Trim ();
                        int len = s.Length;
                        if (len > 0){
                                if (s [0] == '='){
                                        if (len > 2 && s [1] == '='){
                                                s = s.Substring (2);
                                                return va == pp_unary (ref s);
                                        } else {
                                                Error_InvalidDirective ();
                                                return false;
                                        }
                                } else if (s [0] == '!' && len > 1 && s [1] == '='){
                                        s = s.Substring (2);

                                        return va != pp_unary (ref s);

                                } 
                        }

                        return va;
                                
                }
                
                bool pp_and (ref string s)
                {
                        bool va = pp_eq (ref s);

                        s = s.Trim ();
                        int len = s.Length;
                        if (len > 0){
                                if (s [0] == '&'){
                                        if (len > 2 && s [1] == '&'){
                                                s = s.Substring (2);
                                                return (va & pp_and (ref s));
                                        } else {
                                                Error_InvalidDirective ();
                                                return false;
                                        }
                                } 
                        }
                        return va;
                }
                
                //
                // Evaluates an expression for `#if' or `#elif'
                //
                bool pp_expr (ref string s, bool isTerm)
                {
                        bool va = pp_and (ref s);
                        s = s.Trim ();
                        int len = s.Length;
                        if (len > 0){
                                char c = s [0];
                                
                                if (c == '|'){
                                        if (len > 2 && s [1] == '|'){
                                                s = s.Substring (2);
                                                return va | pp_expr (ref s, isTerm);
                                        } else {
                                                Error_InvalidDirective ();
                                                return false;
                                        }
                                }
                                if (isTerm) {
                                        Error_EndLineExpected ();
                                        return false;
                                }
                        }
                        
                        return va;
                }

                bool eval (string s)
                {
                        bool v = pp_expr (ref s, true);
                        s = s.Trim ();
                        if (s.Length != 0){
                                return false;
                        }

                        return v;
                }

                void Error_NumericConstantTooLong ()
                {
                        Report.Error (1021, Location, "Integral constant is too large");                        
                }
                
                void Error_InvalidDirective ()
                {
                        Report.Error (1517, Location, "Invalid preprocessor directive");
                }

                void Error_UnexpectedDirective (string extra)
                {
                        Report.Error (
                                1028, Location,
                                "Unexpected processor directive ({0})", extra);
                }

                void Error_TokensSeen ()
                {
                        Report.Error (1032, Location,
                                "Cannot define or undefine preprocessor symbols after first token in file");
                }

                void Eror_WrongPreprocessorLocation ()
                {
                        Report.Error (1040, Location,
                                "Preprocessor directives must appear as the first non-whitespace character on a line");
                }

                void Error_EndLineExpected ()
                {
                        Report.Error (1025, Location, "Single-line comment or end-of-line expected");
                }

                //
                // Raises a warning when tokenizer found documentation comment
                // on unexpected place
                //
                void WarningMisplacedComment (Location loc)
                {
                        if (doc_state != XmlCommentState.Error) {
                                doc_state = XmlCommentState.Error;
                                Report.Warning (1587, 2, loc, "XML comment is not placed on a valid language element");
                        }
                }
                
                //
                // if true, then the code continues processing the code
                // if false, the code stays in a loop until another directive is
                // reached.
                // When caller_is_taking is false we ignore all directives except the ones
                // which can help us to identify where the #if block ends
                bool ParsePreprocessingDirective (bool caller_is_taking)
                {
                        string arg;
                        bool region_directive = false;

                        var directive = get_cmd_arg (out arg);

                        //
                        // The first group of pre-processing instructions is always processed
                        //
                        switch (directive) {
                        case PreprocessorDirective.Region:
                                region_directive = true;
                                arg = "true";
                                goto case PreprocessorDirective.If;

                        case PreprocessorDirective.Endregion:
                                if (ifstack == null || ifstack.Count == 0){
                                        Error_UnexpectedDirective ("no #region for this #endregion");
                                        return true;
                                }
                                int pop = ifstack.Pop ();
                                        
                                if ((pop & REGION) == 0)
                                        Report.Error (1027, Location, "Expected `#endif' directive");
                                        
                                return caller_is_taking;
                                
                        case PreprocessorDirective.If:
                                if (ifstack == null)
                                        ifstack = new Stack<int> (2);

                                int flags = region_directive ? REGION : 0;
                                if (ifstack.Count == 0){
                                        flags |= PARENT_TAKING;
                                } else {
                                        int state = ifstack.Peek ();
                                        if ((state & TAKING) != 0) {
                                                flags |= PARENT_TAKING;
                                        }
                                }

                                if (eval (arg) && caller_is_taking) {
                                        ifstack.Push (flags | TAKING);
                                        return true;
                                }
                                ifstack.Push (flags);
                                return false;

                        case PreprocessorDirective.Endif:
                                if (ifstack == null || ifstack.Count == 0){
                                        Error_UnexpectedDirective ("no #if for this #endif");
                                        return true;
                                } else {
                                        pop = ifstack.Pop ();
                                        
                                        if ((pop & REGION) != 0)
                                                Report.Error (1038, Location, "#endregion directive expected");
                                        
                                        if (arg.Length != 0) {
                                                Error_EndLineExpected ();
                                        }
                                        
                                        if (ifstack.Count == 0)
                                                return true;

                                        int state = ifstack.Peek ();
                                        return (state & TAKING) != 0;
                                }

                        case PreprocessorDirective.Elif:
                                if (ifstack == null || ifstack.Count == 0){
                                        Error_UnexpectedDirective ("no #if for this #elif");
                                        return true;
                                } else {
                                        int state = ifstack.Pop ();

                                        if ((state & REGION) != 0) {
                                                Report.Error (1038, Location, "#endregion directive expected");
                                                return true;
                                        }

                                        if ((state & ELSE_SEEN) != 0){
                                                Error_UnexpectedDirective ("#elif not valid after #else");
                                                return true;
                                        }

                                        if ((state & TAKING) != 0) {
                                                ifstack.Push (0);
                                                return false;
                                        }

                                        if (eval (arg) && ((state & PARENT_TAKING) != 0)){
                                                ifstack.Push (state | TAKING);
                                                return true;
                                        }

                                        ifstack.Push (state);
                                        return false;
                                }

                        case PreprocessorDirective.Else:
                                if (ifstack == null || ifstack.Count == 0){
                                        Error_UnexpectedDirective ("no #if for this #else");
                                        return true;
                                } else {
                                        int state = ifstack.Peek ();

                                        if ((state & REGION) != 0) {
                                                Report.Error (1038, Location, "#endregion directive expected");
                                                return true;
                                        }

                                        if ((state & ELSE_SEEN) != 0){
                                                Error_UnexpectedDirective ("#else within #else");
                                                return true;
                                        }

                                        ifstack.Pop ();

                                        if (arg.Length != 0) {
                                                Error_EndLineExpected ();
                                                return true;
                                        }

                                        bool ret = false;
                                        if ((state & PARENT_TAKING) != 0) {
                                                ret = (state & TAKING) == 0;
                                        
                                                if (ret)
                                                        state |= TAKING;
                                                else
                                                        state &= ~TAKING;
                                        }
        
                                        ifstack.Push (state | ELSE_SEEN);
                                        
                                        return ret;
                                }
                        case PreprocessorDirective.Define:
                                if (any_token_seen){
                                        Error_TokensSeen ();
                                        return caller_is_taking;
                                }
                                PreProcessDefinition (true, arg, caller_is_taking);
                                return caller_is_taking;

                        case PreprocessorDirective.Undef:
                                if (any_token_seen){
                                        Error_TokensSeen ();
                                        return caller_is_taking;
                                }
                                PreProcessDefinition (false, arg, caller_is_taking);
                                return caller_is_taking;

                        case PreprocessorDirective.Invalid:
                                Report.Error (1024, Location, "Wrong preprocessor directive");
                                return true;
                        }

                        //
                        // These are only processed if we are in a `taking' block
                        //
                        if (!caller_is_taking)
                                return false;
                                        
                        switch (directive){
                        case PreprocessorDirective.Error:
                                Report.Error (1029, Location, "#error: '{0}'", arg);
                                return true;

                        case PreprocessorDirective.Warning:
                                Report.Warning (1030, 1, Location, "#warning: `{0}'", arg);
                                return true;

                        case PreprocessorDirective.Pragma:
                                if (context.Settings.Version == LanguageVersion.ISO_1) {
                                        Report.FeatureIsNotAvailable (context, Location, "#pragma");
                                }

                                ParsePragmaDirective (arg);
                                return true;

                        case PreprocessorDirective.Line:
                                Location loc = Location;
                                if (!PreProcessLine ())
                                        Report.Error (1576, loc, "The line number specified for #line directive is missing or invalid");

                                return caller_is_taking;
                        }

                        throw new NotImplementedException (directive.ToString ());
                }

                private int consume_string (bool quoted)
                {
                        int c;
                        int pos = 0;
                        Location start_location = Location;
                        if (quoted)
                                start_location = start_location - 1;

#if FULL_AST
                        int reader_pos = reader.Position;
#endif

                        while (true){
                                // Cannot use get_char because of \r in quoted strings
                                if (putback_char != -1) {
                                        c = putback_char;
                                        putback_char = -1;
                                } else {
                                        c = reader.Read ();
                                }

                                if (c == '"') {
                                        ++col;

                                        if (quoted && peek_char () == '"') {
                                                if (pos == value_builder.Length)
                                                        Array.Resize (ref value_builder, pos * 2);

                                                value_builder[pos++] = (char) c;
                                                get_char ();
                                                continue;
                                        }

                                        string s;
                                        if (pos == 0)
                                                s = string.Empty;
                                        else if (pos <= 4)
                                                s = InternIdentifier (value_builder, pos);
                                        else
                                                s = new string (value_builder, 0, pos);

                                        ILiteralConstant res = new StringLiteral (context.BuiltinTypes, s, start_location);
                                        val = res;
#if FULL_AST
                                        res.ParsedValue = quoted ?
                                                reader.ReadChars (reader_pos - 2, reader.Position - 1) :
                                                reader.ReadChars (reader_pos - 1, reader.Position);
#endif

                                        return Token.LITERAL;
                                }

                                if (c == '\n') {
                                        if (!quoted) {
                                                Report.Error (1010, Location, "Newline in constant");

                                                advance_line ();

                                                // Don't add \r to string literal
                                                if (pos > 1 && value_builder [pos - 1] == '\r')
                                                        --pos;

                                                val = new StringLiteral (context.BuiltinTypes, new string (value_builder, 0, pos), start_location);
                                                return Token.LITERAL;
                                        }

                                        advance_line ();
                                } else if (c == '\\' && !quoted) {
                                        int surrogate;
                                        c = escape (c, out surrogate);
                                        if (c == -1)
                                                return Token.ERROR;
                                        if (surrogate != 0) {
                                                if (pos == value_builder.Length)
                                                        Array.Resize (ref value_builder, pos * 2);

                                                value_builder[pos++] = (char) c;
                                                c = surrogate;
                                        }
                                } else if (c == -1) {
                                        Report.Error (1039, Location, "Unterminated string literal");
                                        return Token.EOF;
                                } else {
                                        ++col;
                                }

                                if (pos == value_builder.Length)
                                        Array.Resize (ref value_builder, pos * 2);

                                value_builder[pos++] = (char) c;
                        }
                }

                private int consume_identifier (int s)
                {
                        int res = consume_identifier (s, false);

                        if (doc_state == XmlCommentState.Allowed)
                                doc_state = XmlCommentState.NotAllowed;

                        return res;
                }

                int consume_identifier (int c, bool quoted) 
                {
                        //
                        // This method is very performance sensitive. It accounts
                        // for approximately 25% of all parser time
                        //

                        int pos = 0;
                        int column = col;
                        if (quoted)
                                --column;

                        if (c == '\\') {
                                int surrogate;
                                c = escape (c, out surrogate);
                                if (surrogate != 0) {
                                        id_builder [pos++] = (char) c;
                                        c = surrogate;
                                }
                        }

                        id_builder [pos++] = (char) c;

                        try {
                                while (true) {
                                        c = reader.Read ();

                                        if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_' || (c >= '0' && c <= '9')) {
                                                id_builder [pos++] = (char) c;
                                                continue;
                                        }

                                        if (c < 0x80) {
                                                if (c == '\\') {
                                                        int surrogate;
                                                        c = escape (c, out surrogate);
                                                        if (is_identifier_part_character ((char) c))
                                                                id_builder[pos++] = (char) c;

                                                        if (surrogate != 0) {
                                                                c = surrogate;
                                                        }

                                                        continue;
                                                }
                                        } else if (Char.IsLetter ((char) c) || Char.GetUnicodeCategory ((char) c) == UnicodeCategory.ConnectorPunctuation) {
                                                id_builder [pos++] = (char) c;
                                                continue;
                                        }

                                        putback_char = c;
                                        break;
                                }
                        } catch (IndexOutOfRangeException) {
                                Report.Error (645, Location, "Identifier too long (limit is 512 chars)");
                                --pos;
                                col += pos;
                        }

                        col += pos - 1;

                        //
                        // Optimization: avoids doing the keyword lookup
                        // on uppercase letters
                        //
                        if (id_builder [0] >= '_' && !quoted) {
                                int keyword = GetKeyword (id_builder, pos);
                                if (keyword != -1) {
                                        val = ltb.Create (keyword == Token.AWAIT ? "await" : null, current_source, ref_line, column);
                                        return keyword;
                                }
                        }

                        string s = InternIdentifier (id_builder, pos);
                        val = ltb.Create (s, current_source, ref_line, column);
                        if (quoted && parsing_attribute_section)
                                AddEscapedIdentifier (((LocatedToken) val).Location);

                        return Token.IDENTIFIER;
                }

                string InternIdentifier (char[] charBuffer, int length)
                {
                        //
                        // Keep identifiers in an array of hashtables to avoid needless
                        // allocations
                        //
                        var identifiers_group = identifiers[length];
                        string s;
                        if (identifiers_group != null) {
                                if (identifiers_group.TryGetValue (charBuffer, out s)) {
                                        return s;
                                }
                        } else {
                                // TODO: this should be number of files dependant
                                // corlib compilation peaks at 1000 and System.Core at 150
                                int capacity = length > 20 ? 10 : 100;
                                identifiers_group = new Dictionary<char[], string> (capacity, new IdentifiersComparer (length));
                                identifiers[length] = identifiers_group;
                        }

                        char[] chars = new char[length];
                        Array.Copy (charBuffer, chars, length);

                        s = new string (charBuffer, 0, length);
                        identifiers_group.Add (chars, s);
                        return s;
                }
                
                public int xtoken ()
                {
                        int d, c;

                        // Whether we have seen comments on the current line
                        bool comments_seen = false;
                        while ((c = get_char ()) != -1) {
                                switch (c) {
                                case '\t':
                                        col = ((col - 1 + tab_size) / tab_size) * tab_size;
                                        continue;

                                case ' ':
                                case '\f':
                                case '\v':
                                case 0xa0:
                                case 0:
                                case 0xFEFF:    // Ignore BOM anywhere in the file
                                        continue;

/*                              This is required for compatibility with .NET
                                case 0xEF:
                                        if (peek_char () == 0xBB) {
                                                PushPosition ();
                                                get_char ();
                                                if (get_char () == 0xBF)
                                                        continue;
                                                PopPosition ();
                                        }
                                        break;
*/
                                case '\\':
                                        tokens_seen = true;
                                        return consume_identifier (c);

                                case '{':
                                        val = ltb.Create (current_source, ref_line, col);
                                        return Token.OPEN_BRACE;
                                case '}':
                                        val = ltb.Create (current_source, ref_line, col);
                                        return Token.CLOSE_BRACE;
                                case '[':
                                        // To block doccomment inside attribute declaration.
                                        if (doc_state == XmlCommentState.Allowed)
                                                doc_state = XmlCommentState.NotAllowed;

                                        val = ltb.Create (current_source, ref_line, col);

                                        if (parsing_block == 0 || lambda_arguments_parsing)
                                                return Token.OPEN_BRACKET;

                                        int next = peek_char ();
                                        switch (next) {
                                        case ']':
                                        case ',':
                                                return Token.OPEN_BRACKET;

                                        case ' ':
                                        case '\f':
                                        case '\v':
                                        case '\r':
                                        case '\n':
                                        case '/':
                                                next = peek_token ();
                                                if (next == Token.COMMA || next == Token.CLOSE_BRACKET)
                                                        return Token.OPEN_BRACKET;

                                                return Token.OPEN_BRACKET_EXPR;
                                        default:
                                                return Token.OPEN_BRACKET_EXPR;
                                        }
                                case ']':
                                        ltb.CreateOptional (current_source, ref_line, col, ref val);
                                        return Token.CLOSE_BRACKET;
                                case '(':
                                        val = ltb.Create (current_source, ref_line, col);
                                        //
                                        // An expression versions of parens can appear in block context only
                                        //
                                        if (parsing_block != 0 && !lambda_arguments_parsing) {
                                                
                                                //
                                                // Optmize most common case where we know that parens
                                                // is not special
                                                //
                                                switch (current_token) {
                                                case Token.IDENTIFIER:
                                                case Token.IF:
                                                case Token.FOR:
                                                case Token.FOREACH:
                                                case Token.TYPEOF:
                                                case Token.WHILE:
                                                case Token.USING:
                                                case Token.DEFAULT:
                                                case Token.DELEGATE:
                                                case Token.OP_GENERICS_GT:
                                                        return Token.OPEN_PARENS;
                                                }

                                                // Optimize using peek
                                                int xx = peek_char ();
                                                switch (xx) {
                                                case '(':
                                                case '\'':
                                                case '"':
                                                case '0':
                                                case '1':
                                                        return Token.OPEN_PARENS;
                                                }

                                                lambda_arguments_parsing = true;
                                                PushPosition ();
                                                d = TokenizeOpenParens ();
                                                PopPosition ();
                                                lambda_arguments_parsing = false;
                                                return d;
                                        }

                                        return Token.OPEN_PARENS;
                                case ')':
                                        ltb.CreateOptional (current_source, ref_line, col, ref val);
                                        return Token.CLOSE_PARENS;
                                case ',':
                                        ltb.CreateOptional (current_source, ref_line, col, ref val);
                                        return Token.COMMA;
                                case ';':
                                        ltb.CreateOptional (current_source, ref_line, col, ref val);
                                        return Token.SEMICOLON;
                                case '~':
                                        val = ltb.Create (current_source, ref_line, col);
                                        return Token.TILDE;
                                case '?':
                                        val = ltb.Create (current_source, ref_line, col);
                                        return TokenizePossibleNullableType ();
                                case '<':
                                        val = ltb.Create (current_source, ref_line, col);
                                        if (parsing_generic_less_than++ > 0)
                                                return Token.OP_GENERICS_LT;

                                        return TokenizeLessThan ();

                                case '>':
                                        val = ltb.Create (current_source, ref_line, col);
                                        d = peek_char ();

                                        if (d == '='){
                                                get_char ();
                                                return Token.OP_GE;
                                        }

                                        if (parsing_generic_less_than > 1 || (parsing_generic_less_than == 1 && d != '>')) {
                                                parsing_generic_less_than--;
                                                return Token.OP_GENERICS_GT;
                                        }

                                        if (d == '>') {
                                                get_char ();
                                                d = peek_char ();

                                                if (d == '=') {
                                                        get_char ();
                                                        return Token.OP_SHIFT_RIGHT_ASSIGN;
                                                }
                                                return Token.OP_SHIFT_RIGHT;
                                        }

                                        return Token.OP_GT;

                                case '+':
                                        val = ltb.Create (current_source, ref_line, col);
                                        d = peek_char ();
                                        if (d == '+') {
                                                d = Token.OP_INC;
                                        } else if (d == '=') {
                                                d = Token.OP_ADD_ASSIGN;
                                        } else {
                                                return Token.PLUS;
                                        }
                                        get_char ();
                                        return d;

                                case '-':
                                        val = ltb.Create (current_source, ref_line, col);
                                        d = peek_char ();
                                        if (d == '-') {
                                                d = Token.OP_DEC;
                                        } else if (d == '=')
                                                d = Token.OP_SUB_ASSIGN;
                                        else if (d == '>')
                                                d = Token.OP_PTR;
                                        else {
                                                return Token.MINUS;
                                        }
                                        get_char ();
                                        return d;

                                case '!':
                                        val = ltb.Create (current_source, ref_line, col);
                                        if (peek_char () == '='){
                                                get_char ();
                                                return Token.OP_NE;
                                        }
                                        return Token.BANG;

                                case '=':
                                        val = ltb.Create (current_source, ref_line, col);
                                        d = peek_char ();
                                        if (d == '='){
                                                get_char ();
                                                return Token.OP_EQ;
                                        }
                                        if (d == '>'){
                                                get_char ();
                                                return Token.ARROW;
                                        }

                                        return Token.ASSIGN;

                                case '&':
                                        val = ltb.Create (current_source, ref_line, col);
                                        d = peek_char ();
                                        if (d == '&'){
                                                get_char ();
                                                return Token.OP_AND;
                                        }
                                        if (d == '='){
                                                get_char ();
                                                return Token.OP_AND_ASSIGN;
                                        }
                                        return Token.BITWISE_AND;

                                case '|':
                                        val = ltb.Create (current_source, ref_line, col);
                                        d = peek_char ();
                                        if (d == '|'){
                                                get_char ();
                                                return Token.OP_OR;
                                        }
                                        if (d == '='){
                                                get_char ();
                                                return Token.OP_OR_ASSIGN;
                                        }
                                        return Token.BITWISE_OR;

                                case '*':
                                        val = ltb.Create (current_source, ref_line, col);
                                        if (peek_char () == '='){
                                                get_char ();
                                                return Token.OP_MULT_ASSIGN;
                                        }
                                        return Token.STAR;

                                case '/':
                                        d = peek_char ();
                                        if (d == '='){
                                                val = ltb.Create (current_source, ref_line, col);
                                                get_char ();
                                                return Token.OP_DIV_ASSIGN;
                                        }

                                        // Handle double-slash comments.
                                        if (d == '/'){
                                                get_char ();
                                                if (doc_processing) {
                                                        if (peek_char () == '/') {
                                                                get_char ();
                                                                // Don't allow ////.
                                                                if ((d = peek_char ()) != '/') {
                                                                        if (doc_state == XmlCommentState.Allowed)
                                                                                handle_one_line_xml_comment ();
                                                                        else if (doc_state == XmlCommentState.NotAllowed)
                                                                                WarningMisplacedComment (Location - 3);
                                                                }
                                                        } else {
                                                                if (xml_comment_buffer.Length > 0)
                                                                        doc_state = XmlCommentState.NotAllowed;
                                                        }
                                                }

                                                while ((d = get_char ()) != -1 && d != '\n');

                                                any_token_seen |= tokens_seen;
                                                tokens_seen = false;
                                                comments_seen = false;
                                                continue;
                                        } else if (d == '*'){
                                                get_char ();
                                                bool docAppend = false;
                                                if (doc_processing && peek_char () == '*') {
                                                        get_char ();
                                                        // But when it is /**/, just do nothing.
                                                        if (peek_char () == '/') {
                                                                get_char ();
                                                                continue;
                                                        }
                                                        if (doc_state == XmlCommentState.Allowed)
                                                                docAppend = true;
                                                        else if (doc_state == XmlCommentState.NotAllowed) {
                                                                WarningMisplacedComment (Location - 2);
                                                        }
                                                }

                                                int current_comment_start = 0;
                                                if (docAppend) {
                                                        current_comment_start = xml_comment_buffer.Length;
                                                        xml_comment_buffer.Append (Environment.NewLine);
                                                }

                                                while ((d = get_char ()) != -1){
                                                        if (d == '*' && peek_char () == '/'){
                                                                get_char ();
                                                                comments_seen = true;
                                                                break;
                                                        }
                                                        if (docAppend)
                                                                xml_comment_buffer.Append ((char) d);
                                                        
                                                        if (d == '\n'){
                                                                any_token_seen |= tokens_seen;
                                                                tokens_seen = false;
                                                                // 
                                                                // Reset 'comments_seen' just to be consistent.
                                                                // It doesn't matter either way, here.
                                                                //
                                                                comments_seen = false;
                                                        }
                                                }
                                                if (!comments_seen)
                                                        Report.Error (1035, Location, "End-of-file found, '*/' expected");

                                                if (docAppend)
                                                        update_formatted_doc_comment (current_comment_start);
                                                continue;
                                        }
                                        val = ltb.Create (current_source, ref_line, col);
                                        return Token.DIV;

                                case '%':
                                        val = ltb.Create (current_source, ref_line, col);
                                        if (peek_char () == '='){
                                                get_char ();
                                                return Token.OP_MOD_ASSIGN;
                                        }
                                        return Token.PERCENT;

                                case '^':
                                        val = ltb.Create (current_source, ref_line, col);
                                        if (peek_char () == '='){
                                                get_char ();
                                                return Token.OP_XOR_ASSIGN;
                                        }
                                        return Token.CARRET;

                                case ':':
                                        val = ltb.Create (current_source, ref_line, col);
                                        if (peek_char () == ':') {
                                                get_char ();
                                                return Token.DOUBLE_COLON;
                                        }
                                        return Token.COLON;

                                case '0': case '1': case '2': case '3': case '4':
                                case '5': case '6': case '7': case '8': case '9':
                                        tokens_seen = true;
                                        return is_number (c);

                                case '\n': // white space
                                        any_token_seen |= tokens_seen;
                                        tokens_seen = false;
                                        comments_seen = false;
                                        continue;

                                case '.':
                                        tokens_seen = true;
                                        d = peek_char ();
                                        if (d >= '0' && d <= '9')
                                                return is_number (c);

                                        ltb.CreateOptional (current_source, ref_line, col, ref val);
                                        return Token.DOT;
                                
                                case '#':
                                        if (tokens_seen || comments_seen) {
                                                Eror_WrongPreprocessorLocation ();
                                                return Token.ERROR;
                                        }
                                        
                                        if (ParsePreprocessingDirective (true))
                                                continue;

                                        bool directive_expected = false;
                                        while ((c = get_char ()) != -1) {
                                                if (col == 1) {
                                                        directive_expected = true;
                                                } else if (!directive_expected) {
                                                        // TODO: Implement comment support for disabled code and uncomment this code
//                                                      if (c == '#') {
//                                                              Eror_WrongPreprocessorLocation ();
//                                                              return Token.ERROR;
//                                                      }
                                                        continue;
                                                }

                                                if (c == ' ' || c == '\t' || c == '\n' || c == '\f' || c == '\v' )
                                                        continue;

                                                if (c == '#') {
                                                        if (ParsePreprocessingDirective (false))
                                                                break;
                                                }
                                                directive_expected = false;
                                        }

                                        if (c != -1) {
                                                tokens_seen = false;
                                                continue;
                                        }

                                        return Token.EOF;
                                
                                case '"':
                                        return consume_string (false);

                                case '\'':
                                        return TokenizeBackslash ();
                                
                                case '@':
                                        c = get_char ();
                                        if (c == '"') {
                                                tokens_seen = true;
                                                return consume_string (true);
                                        }

                                        if (is_identifier_start_character (c)){
                                                return consume_identifier (c, true);
                                        }

                                        Report.Error (1646, Location, "Keyword, identifier, or string expected after verbatim specifier: @");
                                        return Token.ERROR;

                                case EvalStatementParserCharacter:
                                        return Token.EVAL_STATEMENT_PARSER;
                                case EvalCompilationUnitParserCharacter:
                                        return Token.EVAL_COMPILATION_UNIT_PARSER;
                                case EvalUsingDeclarationsParserCharacter:
                                        return Token.EVAL_USING_DECLARATIONS_UNIT_PARSER;
                                case DocumentationXref:
                                        return Token.DOC_SEE;
                                }

                                if (is_identifier_start_character (c)) {
                                        tokens_seen = true;
                                        return consume_identifier (c);
                                }

                                if (char.IsWhiteSpace ((char) c))
                                        continue;

                                Report.Error (1056, Location, "Unexpected character `{0}'", ((char) c).ToString ());
                        }

                        if (CompleteOnEOF){
                                if (generated)
                                        return Token.COMPLETE_COMPLETION;
                                
                                generated = true;
                                return Token.GENERATE_COMPLETION;
                        }
                        

                        return Token.EOF;
                }

                int TokenizeBackslash ()
                {
#if FULL_AST
                        int read_start = reader.Position;
#endif
                        Location start_location = Location;
                        int c = get_char ();
                        tokens_seen = true;
                        if (c == '\'') {
                                val = new CharLiteral (context.BuiltinTypes, (char) c, start_location);
                                Report.Error (1011, start_location, "Empty character literal");
                                return Token.LITERAL;
                        }

                        if (c == '\n') {
                                Report.Error (1010, start_location, "Newline in constant");
                                return Token.ERROR;
                        }

                        int d;
                        c = escape (c, out d);
                        if (c == -1)
                                return Token.ERROR;
                        if (d != 0)
                                throw new NotImplementedException ();

                        ILiteralConstant res = new CharLiteral (context.BuiltinTypes, (char) c, start_location);
                        val = res;
                        c = get_char ();

                        if (c != '\'') {
                                Report.Error (1012, start_location, "Too many characters in character literal");

                                // Try to recover, read until newline or next "'"
                                while ((c = get_char ()) != -1) {
                                        if (c == '\n' || c == '\'')
                                                break;
                                }
                        }

#if FULL_AST
                        res.ParsedValue = reader.ReadChars (read_start - 1, reader.Position);
#endif

                        return Token.LITERAL;
                }

                int TokenizeLessThan ()
                {
                        int d;
                        if (handle_typeof) {
                                PushPosition ();
                                if (parse_generic_dimension (out d)) {
                                        val = d;
                                        DiscardPosition ();
                                        return Token.GENERIC_DIMENSION;
                                }
                                PopPosition ();
                        }

                        // Save current position and parse next token.
                        PushPosition ();
                        if (parse_less_than ()) {
                                if (parsing_generic_declaration && (parsing_generic_declaration_doc || token () != Token.DOT)) {
                                        d = Token.OP_GENERICS_LT_DECL;
                                } else {
                                        d = Token.OP_GENERICS_LT;
                                }
                                PopPosition ();
                                return d;
                        }

                        PopPosition ();
                        parsing_generic_less_than = 0;

                        d = peek_char ();
                        if (d == '<') {
                                get_char ();
                                d = peek_char ();

                                if (d == '=') {
                                        get_char ();
                                        return Token.OP_SHIFT_LEFT_ASSIGN;
                                }
                                return Token.OP_SHIFT_LEFT;
                        }

                        if (d == '=') {
                                get_char ();
                                return Token.OP_LE;
                        }
                        return Token.OP_LT;
                }

                //
                // Handles one line xml comment
                //
                private void handle_one_line_xml_comment ()
                {
                        int c;
                        while ((c = peek_char ()) == ' ')
                                get_char (); // skip heading whitespaces.
                        while ((c = peek_char ()) != -1 && c != '\n' && c != '\r') {
                                xml_comment_buffer.Append ((char) get_char ());
                        }
                        if (c == '\r' || c == '\n')
                                xml_comment_buffer.Append (Environment.NewLine);
                }

                //
                // Remove heading "*" in Javadoc-like xml documentation.
                //
                private void update_formatted_doc_comment (int current_comment_start)
                {
                        int length = xml_comment_buffer.Length - current_comment_start;
                        string [] lines = xml_comment_buffer.ToString (
                                current_comment_start,
                                length).Replace ("\r", "").Split ('\n');
                        
                        // The first line starts with /**, thus it is not target
                        // for the format check.
                        for (int i = 1; i < lines.Length; i++) {
                                string s = lines [i];
                                int idx = s.IndexOf ('*');
                                string head = null;
                                if (idx < 0) {
                                        if (i < lines.Length - 1)
                                                return;
                                        head = s;
                                } else
                                        head = s.Substring (0, idx);
                                foreach (char c in head)
                                        if (c != ' ')
                                                return;
                                lines [i] = s.Substring (idx + 1);
                        }
                        xml_comment_buffer.Remove (current_comment_start, length);
                        xml_comment_buffer.Insert (current_comment_start, String.Join (Environment.NewLine, lines));
                }

                //
                // Checks if there was incorrect doc comments and raise
                // warnings.
                //
                public void check_incorrect_doc_comment ()
                {
                        if (xml_comment_buffer.Length > 0)
                                WarningMisplacedComment (Location);
                }

                //
                // Consumes the saved xml comment lines (if any)
                // as for current target member or type.
                //
                public string consume_doc_comment ()
                {
                        if (xml_comment_buffer.Length > 0) {
                                string ret = xml_comment_buffer.ToString ();
                                reset_doc_comment ();
                                return ret;
                        }
                        return null;
                }

                Report Report {
                        get { return context.Report; }
                }

                void reset_doc_comment ()
                {
                        xml_comment_buffer.Length = 0;
                }

                public void cleanup ()
                {
                        if (ifstack != null && ifstack.Count >= 1) {
                                int state = ifstack.Pop ();
                                if ((state & REGION) != 0)
                                        Report.Error (1038, Location, "#endregion directive expected");
                                else 
                                        Report.Error (1027, Location, "Expected `#endif' directive");
                        }
                }
        }

        //
        // Indicates whether it accepts XML documentation or not.
        //
        public enum XmlCommentState {
                // comment is allowed in this state.
                Allowed,
                // comment is not allowed in this state.
                NotAllowed,
                // once comments appeared when it is NotAllowed, then the
                // state is changed to it, until the state is changed to
                // .Allowed.
                Error
        }
}