source: branches/2817-BinPackingSpeedup/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory.CSharp-5.5.0/Parser/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
{
  //
  // This class has to be used by parser only, it reuses token
  // details once a file is parsed
  //
  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; }
    }
  }

  /// <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;
      }
    }

    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;
    public CompilationSourceFile SourceFile { get { return source_file; } }
    readonly CompilerContext context;
    readonly Report Report;


    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;
    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;

    const int UnicodeLS = 0x2028;
    const int UnicodePS = 0x2029;
    
    //
    // 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' };
    bool startsLine = true;
    internal SpecialsBag sbag;

    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 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;
      }
      set {
        ref_line = value;
      }
    }

    public int Column {
      get {
        return col;
      }
      set {
        col = value;
      }
    }

    //
    // 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, Report report)
    {
      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);
      this.Report = report;

      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 && current_token != Token.COLON) && !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 || parsing_block == 0) {
            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.DOUBLE:
          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 || next_token == Token.ASSIGN)
              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 ();
        parsing_modifiers = false;
        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 ();
        }

        // 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] = 'p';
        id_builder[1] = 'a';
        id_builder[2] = 'r';
        id_builder[3] = 't';
        id_builder[4] = 'i';
        id_builder[5] = 'a';
        id_builder[6] = 'l';
        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) {
              PopPosition ();
              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 is_identifier_part_character_slow_part (c);
    }

    static bool is_identifier_part_character_slow_part (char c)
    {
      if (Char.IsLetter (c))
        return true;

      switch (Char.GetUnicodeCategory (c)) {
        case UnicodeCategory.ConnectorPunctuation:

        // combining-character: A Unicode character of classes Mn or Mc
        case UnicodeCategory.NonSpacingMark:
        case UnicodeCategory.SpacingCombiningMark:

        // decimal-digit-character: A Unicode character of the class Nd 
        case UnicodeCategory.DecimalDigitNumber:
        return true;
      }

      return false;
    }

    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) {
            if (current_token == Token.SEMICOLON)
              return Token.OPEN_PARENS;

            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:
        case Token.AWAIT:
          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;
    }

    Stack<List<Location>> genericDimensionLocations = new Stack<List<Location>> ();

    public List<Location> GenericDimensionLocations {
      get {
        if (genericDimensionLocations.Count == 0)
          return null;
        return genericDimensionLocations.Pop ();
      }
    }

    bool parse_less_than (ref int genericDimension)
    {
      genericDimensionLocations.Push (new List<Location> ()); 
      genericDimensionLocations.Peek ().Add (Location);
      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:
        genericDimension = 1;
        genericDimensionLocations.Peek ().Add (Location);
        return true;
      case Token.IN:
      case Token.OUT:
        genericDimensionLocations.Pop ();
        return true;
      case Token.COMMA:
        do {
          ++genericDimension;
          if (genericDimensionLocations.Count > 0)
            genericDimensionLocations.Peek ().Add (Location);
          the_token = token ();
        } while (the_token == Token.COMMA);

        if (the_token == Token.OP_GENERICS_GT) {
          ++genericDimension;
          if (genericDimensionLocations.Count > 0)
            genericDimensionLocations.Peek ().Add (Location);
          return true;
        }

        genericDimensionLocations.Pop ();
        return false;
      default:
        genericDimensionLocations.Pop ();
        return false;
      }
      again:
      the_token = token ();
      if (the_token == Token.OP_GENERICS_GT) {
        genericDimensionLocations.Peek ().Add (Location);
        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 (ref genericDimension)) {
          genericDimensionLocations.Pop ();
          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;
        genericDimensionLocations.Pop ();
        return false;
      }

      genericDimensionLocations.Pop ();
      return false;
    }


    public int peek_token ()
    {
      int the_token;

      PushPosition ();
      sbag.Suppress = true;
      the_token = token ();
      sbag.Suppress = false;
      PopPosition ();
      
      return the_token;
    }
          
    //
    // Tonizes `?' using custom disambiguous rules to return one
    // of following tokens: INTERR_NULLABLE, OP_COALESCING, INTERR
    //
    // Tricky expression looks 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;
      }

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

      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;
      int parens = 0;
      int generics = 0;

      var nt = xtoken ();
      switch (nt) {
      case Token.DOT:
      case Token.OPEN_BRACKET_EXPR:
        next_token = Token.INTERR_OPERATOR;
        break;
      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:
      case Token.OP_COALESCING:
      case Token.COLON:
        next_token = Token.INTERR_NULLABLE;
        break;

      case Token.OPEN_PARENS:
      case Token.OPEN_PARENS_CAST:
      case Token.OPEN_PARENS_LAMBDA:
        next_token = -1;
        ++parens;
        break;

      case Token.OP_GENERICS_LT:
      case Token.OP_GENERICS_LT_DECL:
      case Token.GENERIC_DIMENSION:
        next_token = -1;
        ++generics;
        break;

      default:
        next_token = -1;
        break;
      }

      if (next_token == -1) {
        switch (xtoken ()) {
        case Token.COMMA:
        case Token.SEMICOLON:
        case Token.OPEN_BRACE:
        case Token.IN:
          next_token = Token.INTERR_NULLABLE;
          break;
          
        case Token.COLON:
          next_token = Token.INTERR;
          break;

        case Token.OPEN_PARENS:
        case Token.OPEN_PARENS_CAST:
        case Token.OPEN_PARENS_LAMBDA:
          ++parens;
          goto default;

        case Token.CLOSE_PARENS:
          --parens;
          goto default;

        case Token.OP_GENERICS_LT:
        case Token.OP_GENERICS_LT_DECL:
        case Token.GENERIC_DIMENSION:
          ++generics;
          goto default;

        default:
          int ntoken;
          int interrs = 1;
          int colons = 0;
          int braces = 0;
          int brackets = 0;
          //
          // All shorcuts failed, do it hard way
          //
          while ((ntoken = xtoken ()) != Token.EOF) {
            switch (ntoken) {
            case Token.OPEN_BRACE:
              ++braces;
              continue;
            case Token.OPEN_PARENS:
            case Token.OPEN_PARENS_CAST:
            case Token.OPEN_PARENS_LAMBDA:
              ++parens;
              continue;
            case Token.CLOSE_BRACE:
              --braces;
              continue;
            case Token.OP_GENERICS_LT:
            case Token.OP_GENERICS_LT_DECL:
            case Token.GENERIC_DIMENSION:
              ++generics;
              continue;
            case Token.OPEN_BRACKET:
            case Token.OPEN_BRACKET_EXPR:
              ++brackets;
              continue;
            case Token.CLOSE_BRACKET:
              --brackets;
              continue;
            case Token.CLOSE_PARENS:
              if (parens > 0) {
                --parens;
                continue;
              }

              PopPosition ();
              return Token.INTERR_NULLABLE;

            case Token.OP_GENERICS_GT:
              if (generics > 0) {
                --generics;
                continue;
              }

              PopPosition ();
              return Token.INTERR_NULLABLE;
            }

            if (braces != 0)
              continue;

            if (ntoken == Token.SEMICOLON)
              break;

            if (parens != 0)
              continue;

            if (ntoken == Token.COMMA) {
              if (generics != 0 || brackets != 0)
                continue;

              PopPosition ();
              return Token.INTERR_NULLABLE;
            }
            
            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, bool dotLead)
    {
      ILiteralConstant res;

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

      if (!dotLead){
        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 = peek_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 (!dotLead)
          get_char ();

        if (decimal_digits ('.')){
          is_real = true;
          c = peek_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;
        get_char ();
        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 = peek_char ();
      }

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

        if (type != TypeCode.Empty) {
          get_char ();
        }

        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 <= 13) {
        if (x == '\r') {
          if (peek_char () == '\n') {
            putback_char = -1;
            advance_line (SpecialsBag.NewLine.Windows);
          } else {
            advance_line (SpecialsBag.NewLine.Unix);
          }

          x = '\n';
        } else if (x == '\n') {
          advance_line (SpecialsBag.NewLine.Unix);
        } else {
          col++;
        }
      } else if (x >= UnicodeLS && x <= UnicodePS) {
        advance_line (SpecialsBag.NewLine.Unix);
      } else {
        col++;
      }

      return x;
    }

    bool recordNewLine = true;
    void advance_line (SpecialsBag.NewLine newLine)
    {
      if (recordNewLine)
        sbag.AddNewLine (line, col, newLine);
      line++;
      ref_line++;
      previous_col = col;
      col = 0;
      startsLine = true;
    }

    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 || (c >= UnicodeLS && c <= UnicodePS)) {
        // 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)
    {
      int startCol, endLine, endCol;
      return TokenizePreprocessorIdentifier (out c, out startCol, out endLine, out endCol);
    }

    int TokenizePreprocessorIdentifier (out int c, out int startCol, out int endLine, out int endCol)
    {
      // skip over white space
      do {
        endLine = line;
        endCol = col;
        c = get_char ();
      } while (c == ' ' || c == '\t');
      startCol = col;
      int pos = 0;
      while (c != -1 && c >= 'a' && c <= 'z') {
        id_builder[pos++] = (char) c;
        endCol = col + 1;
        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;
      int startLine = line, startCol = col;

      tokens_seen = false;
      arg = "";
      
      int startCol2, endLine, endCol;
      var cmd = GetPreprocessorDirective (id_builder, TokenizePreprocessorIdentifier (out c, out startCol2, out endLine, out endCol));
      
      if ((cmd & PreprocessorDirective.CustomArgumentsParsing) != 0) {
        if (position_stack.Count == 0)
          sbag.AddPreProcessorDirective (startLine, startCol, line, col, cmd, null);
        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' && c != UnicodeLS && c != UnicodePS) {
        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 ();
          ReadToEndOfLine ();
          break;
        }
        
        endLine = line;
        endCol = col + 1;
        
        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);
      }
      if (position_stack.Count == 0)
        sbag.AddPreProcessorDirective (startLine, startCol, endLine, endCol, cmd, arg);

      return cmd;
    }

    //
    // Handles the #line directive
    //
    bool PreProcessLine ()
    {
      Location loc = Location;
      #if FULL_AST
      var lineDirective = sbag.GetCurrentLineProcessorDirective();
      #endif

      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
        //
        ReadToEndOfLine ();
        return false;
      }

      int new_line = TokenizeNumber (c);
      if (new_line < 1) {
        //
        // Eat any remaining characters to continue parsing on next line
        //
        ReadToEndOfLine ();
        return new_line != 0;
      }
      #if FULL_AST
      lineDirective.LineNumber = new_line;
      #endif

      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 != '"' && c != UnicodeLS && c != UnicodePS) {
        //
        // Eat any remaining characters to continue parsing on next line
        //
        ReadToEndOfLine ();

        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);
        #if FULL_AST
        lineDirective.FileName = new_file_name;
        #endif

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

      if (c == '\n' || c == UnicodeLS || c == UnicodePS) {

      } else if (c == '/') {
        ReadSingleLineComment ();
      } else {
        //
        // Eat any remaining characters to continue parsing on next line
        //
        ReadToEndOfLine ();

        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 != UnicodeLS && c != UnicodePS) {
        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
          ReadToEndOfLine ();
        }
      }

      return number;
    }

    void ReadToEndOfLine ()
    {
      int c;
      do {
        c = get_char ();
      } while (c != -1 && c != '\n' && c != UnicodeLS && c != UnicodePS);
    }

    void ReadSingleLineComment ()
    {
      if (peek_char () != '/')
        Report.Warning (1696, 1, Location, "Single-line comment or end-of-line expected");
      if (position_stack.Count == 0)
        sbag.StartComment (SpecialsBag.CommentType.Single, startsLine, line, col - 1);
      // Read everything till the end of the line or file
      int c;
      do {
        c = get_char ();
        if (position_stack.Count == 0)
          sbag.PushCommentChar (c);
        var pc = peek_char ();
        if ((pc == '\n' || pc == -1 || pc == UnicodeLS || pc == UnicodePS) && position_stack.Count == 0) 
          sbag.EndComment (line, col + 1);
      } while (c != -1 && c != '\n' && c != UnicodeLS && c != UnicodePS);
    }

    /// <summary>
    /// Handles #pragma directive
    /// </summary>
    void ParsePragmaDirective ()
    {
      int c;
      int startCol, endLine, endCol;
      int length = TokenizePreprocessorIdentifier (out c, out startCol, out endLine, out endCol);
      #if FULL_AST
      var pragmaDirective = sbag.GetPragmaPreProcessorDirective();
      if (pragmaDirective != null)
        pragmaDirective.WarningColumn = startCol;
      #endif
      if (length == pragma_warning.Length && IsTokenIdentifierEqual (pragma_warning)) {
        length = TokenizePreprocessorIdentifier (out c, out startCol, out endLine, out endCol);
        #if FULL_AST
        if (pragmaDirective != null)
          pragmaDirective.DisableRestoreColumn = startCol;
        #endif

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

            var loc = Location;

            if (c == '\n' || c == '/' || c == UnicodeLS || c == UnicodePS) {
              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 {
                var startLoc = loc;
                #if FULL_AST
                // int read_start = reader.Position;
                #endif
                code = TokenizePragmaNumber (ref c);
                if (code > 0) {
                  #if FULL_AST
                  var literal = new IntConstant(context.BuiltinTypes, code, startLoc);
                  if (pragmaDirective != null)
                    pragmaDirective.Codes.Add (literal);
                //  literal.ParsedValue = reader.ReadChars (read_start, reader.Position + 1);
                  #endif
                  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 && c != UnicodeLS && c != UnicodePS);
            }

            return;
          }
        }

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

        // Eat any remaining characters on the line
        ReadToEndOfLine ();

        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;
        }
        sbag.SkipIf ();
        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) {
            sbag.SkipIf ();
            ifstack.Push (0);
            return false;
          }

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

          sbag.SkipIf ();
          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){
          if (caller_is_taking)
            Error_TokensSeen ();
          return caller_is_taking;
        }
        PreProcessDefinition (true, arg, caller_is_taking);
        return caller_is_taking;

      case PreprocessorDirective.Undef:
        if (any_token_seen){
          if (caller_is_taking)
            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 ();
        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;
        recordNewLine = false;
      }

#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
          recordNewLine = true;
          return Token.LITERAL;
        }

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


            // Don't add \r to string literal
            if (pos > 1 && value_builder [pos - 1] == '\r') {
              advance_line (SpecialsBag.NewLine.Windows);
              --pos;
            } else {
              advance_line (SpecialsBag.NewLine.Unix);
            }

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

          advance_line (SpecialsBag.NewLine.Unix);
        } else if (c == '\\' && !quoted) {
          ++col;
          int surrogate;
          c = escape (c, out surrogate);
          if (c == -1) {
            recordNewLine = true;
            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");
          recordNewLine = true;
          return Token.EOF;
        } else {
          ++col;
        }

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

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

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

      if (doc_state == XmlCommentState.Allowed)
        doc_state = XmlCommentState.NotAllowed;
      startsLine = false;
      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 (is_identifier_part_character_slow_part ((char) c)) {
            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);
#if FULL_AST
      if (quoted) {
        val = ltb.Create ("@" + s, current_source, ref_line, column - 1);
      } else {
        val = ltb.Create (s, current_source, ref_line, column);
      }
#else
      val = ltb.Create (s, current_source, ref_line, column);
#endif
      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 UnicodeLS:
          case UnicodePS:
          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.SWITCH:
            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 (position_stack.Count == 0)
                    sbag.PushCommentChar (d);
                  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;
              }
            } else {
              bool isDoc = peek_char () == '/';
              if (position_stack.Count == 0)
                sbag.StartComment (isDoc ? SpecialsBag.CommentType.Documentation : SpecialsBag.CommentType.Single, startsLine, line, col - 1);
              if (isDoc)
                get_char ();
            }
            
            d = peek_char ();
            int endLine = line, endCol = col;
            while ((d = get_char ()) != -1 && (d != '\n') && d != '\r' && d != UnicodePS && d != UnicodeLS) {
              if (position_stack.Count == 0)
                sbag.PushCommentChar (d);
              endLine = line;
              endCol = col;
            }
            if (position_stack.Count == 0)
              sbag.EndComment (endLine, endCol + 1);
            any_token_seen |= tokens_seen;
            tokens_seen = false;
            comments_seen = false;
            continue;
          } else if (d == '*'){
            if (position_stack.Count == 0) {
              sbag.StartComment (SpecialsBag.CommentType.Multi, startsLine, line, col);
              recordNewLine = false;
            }
            get_char ();
            bool docAppend = false;
            if (doc_processing && peek_char () == '*') {
              int ch = get_char ();
              // But when it is /**/, just do nothing.
              if (peek_char () == '/') {
                ch = get_char ();
                if (position_stack.Count == 0) {
                  recordNewLine = true;
                  sbag.EndComment (line, col + 1);
                }
                continue;
              } else {
                if (position_stack.Count == 0)
                  sbag.PushCommentChar (ch);
              }
              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 ();
                if (position_stack.Count == 0) {
                  recordNewLine = true;
                  sbag.EndComment (line, col + 1);
                }
                comments_seen = true;
                break;
              } else {
                if (position_stack.Count == 0)
                  sbag.PushCommentChar (d);
              }
              if (docAppend)
                xml_comment_buffer.Append ((char) d);
              
              if (d == '\n' || d == UnicodeLS || d == UnicodePS){
                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, false);

        case '\n': // white space
        case UnicodeLS:
        case UnicodePS:
          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, true);

          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;
          sbag.StartComment(SpecialsBag.CommentType.InactiveCode, false, line, 1);
          recordNewLine = false;
          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;
//              }
              if (c != '#')
                sbag.PushCommentChar (c);
              continue;
            }

            if (c == ' ' || c == '\t' || c == '\n' || c == '\f' || c == '\v' || c == UnicodeLS || c == UnicodePS) {
              sbag.PushCommentChar (c);
              continue;
            }

            if (c == '#') {
              var oldNL = recordNewLine;
              recordNewLine = true;
              var continueNormalLexing = ParsePreprocessingDirective(false);
              recordNewLine = oldNL;
              if (continueNormalLexing)
                break;
              sbag.StartComment(SpecialsBag.CommentType.InactiveCode, false, line, 1);
            }
            sbag.PushCommentChar (c);
            directive_expected = false;
          }
          recordNewLine = true;
          sbag.EndComment (line, col);
          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' || c == UnicodeLS || c == UnicodePS) {
        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 == '\'' || c == UnicodeLS || c == UnicodePS)
            break;
        }
      }

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

      return Token.LITERAL;
    }

    int TokenizeLessThan ()
    {
      int d;

      // Save current position and parse next token.
      PushPosition ();
      int generic_dimension = 0;
      if (parse_less_than (ref generic_dimension)) {
        if (parsing_generic_declaration && (parsing_generic_declaration_doc || token () != Token.DOT)) {
          d = Token.OP_GENERICS_LT_DECL;
        } else {
          if (generic_dimension > 0) {
            val = generic_dimension;
            DiscardPosition ();
            return Token.GENERIC_DIMENSION;
          }

          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 ()) == ' ') {
        if (position_stack.Count == 0)
          sbag.PushCommentChar (c);
        get_char (); // skip heading whitespaces.
      }
      while ((c = peek_char ()) != -1 && c != '\n' && c != '\r') {
        if (position_stack.Count == 0)
          sbag.PushCommentChar (c);
        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;
    }

    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
  }
}