assemblyscript/src/parser.ts

/*

 This is a custom parser specifically written for the AssemblyScript subset. It
 accepts some of the most common TypeScript-only patterns that it knows an
 appropriate error message for but, though it uses TypeScript's codes for
 diagnostics, doesn't ultimately aim at full compatibility.

*/

import {
  Program
} from "./program";

import {
  Tokenizer,
  Token,
  Range
} from "./tokenizer";

import {
  DiagnosticCode,
  DiagnosticEmitter
} from "./diagnostics";

import {
  normalize as normalizePath
} from "./util/path";

import {
  Node,
  NodeKind,
  Source,
  TypeNode,
  // expressions
  AssertionKind,
  CallExpression,
  Expression,
  IdentifierExpression,
  StringLiteralExpression,
  // statements
  BlockStatement,
  BreakStatement,
  ClassDeclaration,
  ContinueStatement,
  DeclarationStatement,
  Decorator,
  DoStatement,
  EnumDeclaration,
  EnumValueDeclaration,
  ExportImportStatement,
  ExportMember,
  ExportStatement,
  ExpressionStatement,
  FieldDeclaration,
  ForStatement,
  FunctionDeclaration,
  IfStatement,
  ImportDeclaration,
  ImportStatement,
  MethodDeclaration,
  Modifier,
  ModifierKind,
  NamespaceDeclaration,
  Parameter,
  ReturnStatement,
  Statement,
  SwitchCase,
  SwitchStatement,
  ThrowStatement,
  TryStatement,
  TypeDeclaration,
  TypeParameter,
  VariableStatement,
  VariableDeclaration,
  WhileStatement,
  // utility
  addModifier,
  getModifier,
  hasModifier,
  setReusableModifiers
} from "./ast";

/** Parser interface. */
export class Parser extends DiagnosticEmitter {

  /** Program being created. */
  program: Program;
  /** Log of source file names to be requested. */
  backlog: string[] = new Array();
  /** Log of source file names already processed. */
  seenlog: Set<string> = new Set();

  /** Constructs a new parser. */
  constructor() {
    super();
    this.program = new Program(this.diagnostics);
  }

  /** Parses a file and adds its definitions to the program. */
  parseFile(text: string, path: string, isEntry: bool): void {
    var normalizedPath = normalizePath(path);
    for (var i = 0, k = this.program.sources.length; i < k; ++i)
      if (this.program.sources[i].normalizedPath == normalizedPath)
        return; // already parsed
    this.seenlog.add(normalizedPath);

    var source = new Source(path, text, isEntry);
    this.program.sources.push(source);

    var tn = new Tokenizer(source, this.program.diagnostics);
    source.tokenizer = tn;

    while (!tn.skip(Token.ENDOFFILE)) {
      var statement = this.parseTopLevelStatement(tn);
      if (statement) {
        statement.parent = source;
        source.statements.push(statement);
      }
    }
  }

  parseTopLevelStatement(tn: Tokenizer, isNamespaceMember: bool = false): Statement | null {
    var decorators: Decorator[] | null = null;

    while (tn.skip(Token.AT)) {
      var decorator = this.parseDecorator(tn);
      if (!decorator)
        break;
      if (!decorators)
        decorators = new Array();
      (<Decorator[]>decorators).push(<Decorator>decorator);
    }

    var modifiers: Modifier[] | null = null;

    if (tn.skip(Token.EXPORT))
      modifiers = addModifier(Node.createModifier(ModifierKind.EXPORT, tn.range()), modifiers);

    if (tn.skip(Token.DECLARE)) {
      modifiers = addModifier(Node.createModifier(ModifierKind.DECLARE, tn.range()), modifiers);
      tn.peek(true);
      if (tn.nextTokenOnNewLine)
        this.error(DiagnosticCode.Line_break_not_permitted_here, tn.range(tn.pos)); // recoverable, compatibility
    }

    tn.mark();

    var statement: Statement | null = null;
    var modifier: Modifier | null;
    switch (tn.next()) {

      case Token.CONST:
        modifiers = addModifier(Node.createModifier(ModifierKind.CONST, tn.range()), modifiers);

        if (tn.skip(Token.ENUM)) {
          statement = this.parseEnum(tn, modifiers, decorators);
          break;
        }
        // fall through

      case Token.VAR:
      case Token.LET:
        statement = this.parseVariable(tn, modifiers, decorators);
        decorators = null;
        break;

      case Token.ENUM:
        statement = this.parseEnum(tn, modifiers, decorators);
        decorators = null;
        break;

      case Token.FUNCTION:
        statement = this.parseFunction(tn, modifiers, decorators);
        decorators = null;
        break;

      case Token.ABSTRACT:
        if (!tn.skip(Token.CLASS)) {
          this.error(DiagnosticCode._0_expected, tn.range(tn.pos), "class");
          break;
        }
        modifiers = addModifier(Node.createModifier(ModifierKind.ABSTRACT, tn.range()), modifiers);
        // fall through

      case Token.CLASS:
        statement = this.parseClass(tn, modifiers, decorators);
        decorators = null;
        break;

      case Token.NAMESPACE:
        statement = this.parseNamespace(tn, modifiers, decorators);
        decorators = null;
        break;

      case Token.IMPORT:
        if (modifier = getModifier(ModifierKind.EXPORT, modifiers)) {
          statement = this.parseExportImport(tn, modifier.range);
        } else
          statement = this.parseImport(tn);
        if (modifiers)
          setReusableModifiers(modifiers);
        break;

      case Token.TYPE:
        statement = this.parseTypeDeclaration(tn, modifiers, decorators);
        decorators = null;
        break;

      default:
        if (hasModifier(ModifierKind.EXPORT, modifiers)) {
          tn.reset();
          statement = this.parseExport(tn, modifiers); // TODO: why exactly does this have modifiers again? 'declare'?
        } else {
          if (modifiers) {
            if (modifier = getModifier(ModifierKind.DECLARE, modifiers))
              this.error(DiagnosticCode._0_modifier_cannot_be_used_here, modifier.range, "declare"); // recoverable
            setReusableModifiers(modifiers);
          }
          tn.reset();
          if (!isNamespaceMember)
            statement = this.parseStatement(tn, true);
        }
        break;
    }

    if (decorators /* not consumed */)
      for (var i = 0, k = (<Decorator[]>decorators).length; i < k; ++i)
        this.error(DiagnosticCode.Decorators_are_not_valid_here, (<Decorator[]>decorators)[i].range);

    return statement;
  }

  /** Obtains the next file to parse. */
  nextFile(): string | null {
    if (this.backlog.length) {
      var filename = this.backlog[0];
      for (var i = 0, k = this.backlog.length - 1; i < k; ++i)
        this.backlog[i] = this.backlog[i + 1];
      this.backlog.length--;
      return filename;
    }
    return null;
  }

  /** Finishes parsing and returns the program. */
  finish(): Program {
    if (this.backlog.length)
      throw new Error("backlog is not empty");
    this.backlog = [];
    this.seenlog.clear();
    return this.program;
  }

  parseType(tn: Tokenizer, acceptParenthesized: bool = true, suppressErrors: bool = false): TypeNode | null {
    // not TypeScript-compatible
    var token = tn.next();
    var startPos = tn.tokenPos;

    // void
    if (token == Token.VOID)
      return Node.createType(Node.createIdentifier("void", tn.range()), [], false, tn.range(startPos, tn.pos));

    var type: TypeNode;

    // ( ... )
    if (acceptParenthesized && token == Token.OPENPAREN) {
      var innerType = this.parseType(tn, false, suppressErrors);
      if (!innerType)
        return null;
      if (!tn.skip(Token.CLOSEPAREN)) {
        if (!suppressErrors)
          this.error(DiagnosticCode._0_expected, tn.range(tn.pos), "}");
        return null;
      }
      type = innerType;
      type.range.start = startPos;
      type.range.end = tn.pos;

    // this
    } else if (token == Token.THIS) {
      type = Node.createType(Node.createThis(tn.range()), [], false, tn.range(startPos, tn.pos));

    // true
    } else if (token == Token.TRUE || token == Token.FALSE) {
      type = Node.createType(Node.createIdentifier("bool", tn.range()), [], false, tn.range(startPos, tn.pos));

    // string literal
    } else if (token == Token.STRINGLITERAL) {
      tn.readString();
      type = Node.createType(Node.createIdentifier("string", tn.range()), [], false, tn.range(startPos, tn.pos));

    // Name
    } else if (token == Token.IDENTIFIER) {
      var identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
      var parameters = new Array<TypeNode>();
      var nullable = false;

      // Name<T>
      if (tn.skip(Token.LESSTHAN)) {
        do {
          var parameter = this.parseType(tn, true, suppressErrors);
          if (!parameter)
            return null;
          parameters.push(<TypeNode>parameter);
        } while (tn.skip(Token.COMMA));
        if (!tn.skip(Token.GREATERTHAN)) {
          if (!suppressErrors)
            this.error(DiagnosticCode._0_expected, tn.range(tn.pos), ">");
          return null;
        }
      }
      // ... | null
      if (tn.skip(Token.BAR)) {
        if (tn.skip(Token.NULL)) {
          nullable = true;
        } else {
          if (!suppressErrors)
            this.error(DiagnosticCode._0_expected, tn.range(tn.pos), "null");
          return null;
        }
      }
      type = Node.createType(identifier, parameters, nullable, tn.range(startPos, tn.pos));

    } else {
      if (!suppressErrors)
        this.error(DiagnosticCode.Identifier_expected, tn.range());
      return null;
    }
    // ... [][]
    while (tn.skip(Token.OPENBRACKET)) {
      var bracketStart = tn.tokenPos;
      if (!tn.skip(Token.CLOSEBRACKET)) {
        if (!suppressErrors)
          this.error(DiagnosticCode._0_expected, tn.range(), "]");
        return null;
      }
      var bracketRange = tn.range(bracketStart, tn.pos);

      // ...[] | null
      nullable = false;
      if (tn.skip(Token.BAR)) {
        if (tn.skip(Token.NULL)) {
          nullable = true;
        } else {
          if (!suppressErrors)
            this.error(DiagnosticCode._0_expected, tn.range(), "null");
          return null;
        }
      }
      type = Node.createType(Node.createIdentifier("Array", bracketRange), [ type ], nullable, tn.range(startPos, tn.pos));
      if (nullable)
        break;
    }

    return type;
  }

  // statements

  parseDecorator(tn: Tokenizer): Decorator | null {
    // at '@': Identifier ('.' Identifier)* '(' Arguments
    var startPos = tn.tokenPos;
    if (tn.skip(Token.IDENTIFIER)) {
      var name = tn.readIdentifier();
      var expression: Expression = Node.createIdentifier(name, tn.range(startPos, tn.pos));
      while (tn.skip(Token.DOT)) {
        if (tn.skip(Token.IDENTIFIER)) {
          name = tn.readIdentifier();
          expression = Node.createPropertyAccess(expression, Node.createIdentifier(name, tn.range()), tn.range(startPos, tn.pos));
        } else {
          this.error(DiagnosticCode.Identifier_expected, tn.range());
          return null;
        }
      }
      if (tn.skip(Token.OPENPAREN)) {
        var args = this.parseArguments(tn);
        if (args)
          return Node.createDecorator(expression, <Expression[]>args, tn.range(startPos, tn.pos));
      } else
        this.error(DiagnosticCode._0_expected, tn.range(), "(");
    } else
      this.error(DiagnosticCode.Identifier_expected, tn.range());
    return null;
  }

  parseVariable(tn: Tokenizer, modifiers: Modifier[] | null, decorators: Decorator[] | null): VariableStatement | null {
    // at ('const' | 'let' | 'var'): VariableDeclaration (',' VariableDeclaration)* ';'?
    var startPos = modifiers && modifiers.length ? modifiers[0].range.start : tn.tokenPos;
    var members = new Array<VariableDeclaration>();
    var isDeclare = hasModifier(ModifierKind.DECLARE, modifiers);
    do {
      var member = this.parseVariableDeclaration(tn, isDeclare, modifiers, decorators);
      if (!member)
        return null;
      members.push(<VariableDeclaration>member);
    } while (tn.skip(Token.COMMA));

    var ret = Node.createVariable(members, modifiers, decorators, tn.range(startPos, tn.pos));
    tn.skip(Token.SEMICOLON);
    return ret;
  }

  parseVariableDeclaration(tn: Tokenizer, isDeclare: bool = false, parentModifiers: Modifier[] | null, parentDecorators: Decorator[] | null): VariableDeclaration | null {
    // Identifier (':' Type)? ('=' Expression)?
    if (!tn.skip(Token.IDENTIFIER)) {
      this.error(DiagnosticCode.Identifier_expected, tn.range());
      return null;
    }
    var identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());

    var type: TypeNode | null = null;
    if (tn.skip(Token.COLON))
      type = this.parseType(tn);

    var initializer: Expression | null = null;
    if (tn.skip(Token.EQUALS)) {
      if (isDeclare)
        this.error(DiagnosticCode.Initializers_are_not_allowed_in_ambient_contexts, tn.range()); // recoverable
      initializer = this.parseExpression(tn, Precedence.COMMA + 1);
      if (!initializer)
        return null;
    } else {
      if (hasModifier(ModifierKind.CONST, parentModifiers)) {
        if (!hasModifier(ModifierKind.DECLARE, parentModifiers))
          this.error(DiagnosticCode._const_declarations_must_be_initialized, identifier.range);
      } else if (!type) // neither type nor initializer
        this.error(DiagnosticCode.Type_expected, tn.range(tn.pos)); // recoverable
    }
    return Node.createVariableDeclaration(identifier, type, initializer, parentModifiers, parentDecorators, Range.join(identifier.range, tn.range()));
  }

  parseEnum(tn: Tokenizer, modifiers: Modifier[] | null, decorators: Decorator[] | null): EnumDeclaration | null {
    // at 'enum': Identifier '{' (EnumValueDeclaration (',' EnumValueDeclaration )*)? '}' ';'?
    var startPos = modifiers && modifiers.length ? modifiers[0].range.start : tn.tokenPos;
    if (tn.next() != Token.IDENTIFIER) {
      this.error(DiagnosticCode.Identifier_expected, tn.range());
      return null;
    }
    var identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
    if (tn.next() != Token.OPENBRACE) {
      this.error(DiagnosticCode._0_expected, tn.range(), "{");
      return null;
    }
    var members = new Array<EnumValueDeclaration>();
    if (!tn.skip(Token.CLOSEBRACE)) {
      do {
        var member = this.parseEnumValue(tn);
        if (!member)
          return null;
        members.push(<EnumValueDeclaration>member);
      } while (tn.skip(Token.COMMA));
      if (!tn.skip(Token.CLOSEBRACE)) {
        this.error(DiagnosticCode._0_expected, tn.range(), "}");
        return null;
      }
    }
    var ret = Node.createEnum(identifier, members, modifiers, decorators, tn.range(startPos, tn.pos));
    tn.skip(Token.SEMICOLON);
    return ret;
  }

  parseEnumValue(tn: Tokenizer): EnumValueDeclaration | null {
    // Identifier ('=' Expression)?
    if (!tn.skip(Token.IDENTIFIER)) {
      this.error(DiagnosticCode.Identifier_expected, tn.range());
      return null;
    }
    var identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
    var value: Expression | null = null;
    if (tn.skip(Token.EQUALS)) {
      value = this.parseExpression(tn, Precedence.COMMA + 1);
      if (!value)
        return null;
    }
    return Node.createEnumValue(identifier, value, Range.join(identifier.range, tn.range()));
  }

  parseReturn(tn: Tokenizer): ReturnStatement | null {
    // at 'return': Expression | (';' | '}' | ...'\n')
    var expr: Expression | null = null;
    if (tn.peek(true) != Token.SEMICOLON && tn.nextToken != Token.CLOSEBRACE && !tn.nextTokenOnNewLine) {
      expr = this.parseExpression(tn);
      if (!expr)
        return null;
    }
    var ret = Node.createReturn(expr, tn.range());
    tn.skip(Token.SEMICOLON);
    return ret;
  }

  parseTypeParameters(tn: Tokenizer): TypeParameter[] | null {
    // at '<': TypeParameter (',' TypeParameter)* '>'
    var typeParameters = new Array<TypeParameter>();
    if (!tn.skip(Token.GREATERTHAN)) {
      do {
        var typeParameter = this.parseTypeParameter(tn);
        if (!typeParameter)
          return null;
        typeParameters.push(<TypeParameter>typeParameter);
      } while (tn.skip(Token.COMMA));
      if (!tn.skip(Token.GREATERTHAN)) {
        this.error(DiagnosticCode._0_expected, tn.range(), ">");
        return null;
      }
    } else
      this.error(DiagnosticCode.Type_parameter_list_cannot_be_empty, tn.range()); // recoverable
    return typeParameters;
  }

  parseTypeParameter(tn: Tokenizer): TypeParameter | null {
    // Identifier ('extends' Type)?
    if (tn.next() == Token.IDENTIFIER) {
      var identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
      var extendsType: TypeNode | null = null;
      if (tn.skip(Token.EXTENDS)) {
        extendsType = this.parseType(tn);
        if (!extendsType)
          return null;
      }
      return Node.createTypeParameter(identifier, extendsType, Range.join(identifier.range, tn.range()));
    } else
      this.error(DiagnosticCode.Identifier_expected, tn.range());
    return null;
  }

  parseParameters(tn: Tokenizer): Parameter[] | null {
    // at '(': (Parameter (',' Parameter)*)? ')'
    var parameters = new Array<Parameter>();
    if (tn.peek() != Token.CLOSEPAREN) {
      do {
        var param = this.parseParameter(tn);
        if (!param)
          return null;
        parameters.push(<Parameter>param);
      } while (tn.skip(Token.COMMA));
    }
    if (tn.skip(Token.CLOSEPAREN))
      return parameters;
    else
      this.error(DiagnosticCode._0_expected, tn.range(), ")");
    return null;
  }

  parseParameter(tn: Tokenizer): Parameter | null {
    // '...'? Identifier (':' Type)? ('=' Expression)?
    var isRest = false;
    var startRange: Range | null = null;
    if (tn.skip(Token.DOT_DOT_DOT)) {
      isRest = true;
      startRange = tn.range();
    }
    if (tn.skip(Token.IDENTIFIER)) {
      if (!isRest)
        startRange = tn.range();
      var identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
      var type: TypeNode | null = null;
      if (tn.skip(Token.COLON)) {
        type = this.parseType(tn);
        if (!type)
          return null;
      }
      var initializer: Expression | null = null;
      if (tn.skip(Token.EQUALS)) {
        initializer = this.parseExpression(tn);
        if (!initializer)
          return null;
      }
      return Node.createParameter(identifier, type, initializer, isRest, Range.join(<Range>startRange, tn.range()));
    } else
      this.error(DiagnosticCode.Identifier_expected, tn.range());
    return null;
  }

  parseFunction(tn: Tokenizer, modifiers: Modifier[] | null, decorators: Decorator[] | null): FunctionDeclaration | null {
    // at 'function': Identifier ('<' TypeParameters)? '(' Parameters (':' Type)? '{' Statement* '}' ';'?
    var startPos = modifiers && modifiers.length ? modifiers[0].range.start : tn.tokenPos;

    if (!tn.skip(Token.IDENTIFIER)) {
      this.error(DiagnosticCode.Identifier_expected, tn.range(tn.pos));
      return null;
    }
    var identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
    var typeParameters: TypeParameter[] | null = null;
    if (tn.skip(Token.LESSTHAN)) {
      typeParameters = this.parseTypeParameters(tn);
      if (!typeParameters)
        return null;
    } else
      typeParameters = [];
    if (!tn.skip(Token.OPENPAREN)) {
      this.error(DiagnosticCode._0_expected, tn.range(tn.pos), "(");
      return null;
    }
    var parameters = this.parseParameters(tn);
    if (!parameters)
      return null;
    var isSetter = hasModifier(ModifierKind.SET, modifiers);
    if (isSetter) {
      if (parameters.length != 1)
        this.error(DiagnosticCode.A_set_accessor_must_have_exactly_one_parameter, identifier.range); // recoverable
      if (parameters.length && parameters[0].initializer)
        this.error(DiagnosticCode.A_set_accessor_parameter_cannot_have_an_initializer, identifier.range); // recoverable
    }
    var isGetter = hasModifier(ModifierKind.GET, modifiers);
    if (isGetter && parameters.length)
      this.error(DiagnosticCode.A_get_accessor_cannot_have_parameters, identifier.range); // recoverable
    var returnType: TypeNode | null = null;
    if (tn.skip(Token.COLON)) {
      returnType = this.parseType(tn, isSetter);
      if (!returnType)
        return null;
    } else if (!isSetter) {
      this.error(DiagnosticCode.Type_expected, tn.range(tn.pos)); // recoverable
    }
    var isDeclare = hasModifier(ModifierKind.DECLARE, modifiers);
    var statements: Statement[] | null = null;
    if (tn.skip(Token.OPENBRACE)) {
      statements = new Array();
      if (isDeclare)
        this.error(DiagnosticCode.An_implementation_cannot_be_declared_in_ambient_contexts, tn.range()); // recoverable
      while (!tn.skip(Token.CLOSEBRACE)) {
        var statement = this.parseStatement(tn);
        if (!statement)
          return null;
        statements.push(<Statement>statement);
      }
    } else if (!isDeclare)
      this.error(DiagnosticCode.Function_implementation_is_missing_or_not_immediately_following_the_declaration, tn.range(tn.pos));
    var ret = Node.createFunction(identifier, typeParameters, <Parameter[]>parameters, returnType, statements, modifiers, decorators, tn.range(startPos, tn.pos));
    tn.skip(Token.SEMICOLON);
    return ret;
  }

  parseClass(tn: Tokenizer, modifiers: Modifier[] | null, decorators: Decorator[] | null): ClassDeclaration | null {
    // at 'class': Identifier ('<' TypeParameters)? ('extends' Type)? ('implements' Type (',' Type)*)? '{' ClassMember* '}'
    var startPos = decorators && decorators.length
      ? decorators[0].range.start
      : modifiers && modifiers.length
      ? modifiers[0].range.start
      : tn.tokenPos;

    if (tn.skip(Token.IDENTIFIER)) {
      var identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
      var typeParameters: TypeParameter[] | null;

      if (tn.skip(Token.LESSTHAN)) {
        typeParameters = this.parseTypeParameters(tn);
        if (!typeParameters)
          return null;
      } else
        typeParameters = [];

      var extendsType: TypeNode | null = null;
      if (tn.skip(Token.EXTENDS)) {
        extendsType = this.parseType(tn);
        if (!extendsType)
          return null;
      }

      var implementsTypes = new Array<TypeNode>();
      if (tn.skip(Token.IMPLEMENTS)) {
        do {
          var type = this.parseType(tn);
          if (!type)
            return null;
          implementsTypes.push(<TypeNode>type);
        } while (tn.skip(Token.COMMA));
      }

      if (tn.skip(Token.OPENBRACE)) {
        var members = new Array<DeclarationStatement>();
        if (!tn.skip(Token.CLOSEBRACE)) {
          var isDeclare = hasModifier(ModifierKind.DECLARE, modifiers);
          do {
            var member = this.parseClassMember(tn, isDeclare);
            if (!member)
              return null;
            members.push(<DeclarationStatement>member);
          } while (!tn.skip(Token.CLOSEBRACE));
        }
        return Node.createClass(identifier, <TypeParameter[]>typeParameters, extendsType, implementsTypes, members, modifiers, decorators, tn.range(startPos, tn.pos));
      } else
        this.error(DiagnosticCode._0_expected, tn.range(), "{");
    } else
      this.error(DiagnosticCode.Identifier_expected, tn.range());
    return null;
  }

  parseClassMember(tn: Tokenizer, parentIsDeclare: bool): DeclarationStatement | null {
    // ('public' | 'private' | 'protected')? ('static' | 'abstract')? ('get' | 'set')? Identifier ...
    var startPos = tn.pos;

    var decorators = new Array<Decorator>();

    while (tn.skip(Token.AT)) {
      var decorator = this.parseDecorator(tn);
      if (!decorator)
        break;
      decorators.push(<Decorator>decorator);
    }

    var modifiers: Modifier[] | null = null;

    if (tn.skip(Token.PUBLIC))
      modifiers = addModifier(Node.createModifier(ModifierKind.PUBLIC, tn.range()), modifiers);
    else if (tn.skip(Token.PRIVATE))
      modifiers = addModifier(Node.createModifier(ModifierKind.PRIVATE, tn.range()), modifiers);
    else if (tn.skip(Token.PROTECTED))
      modifiers = addModifier(Node.createModifier(ModifierKind.PROTECTED, tn.range()), modifiers);

    if (tn.skip(Token.STATIC))
      modifiers = addModifier(Node.createModifier(ModifierKind.STATIC, tn.range()), modifiers);
    else if (tn.skip(Token.ABSTRACT))
      modifiers = addModifier(Node.createModifier(ModifierKind.ABSTRACT, tn.range()), modifiers);

    if (tn.skip(Token.READONLY))
      modifiers = addModifier(Node.createModifier(ModifierKind.READONLY, tn.range()), modifiers);

    var isGetter = false;
    var isSetter = false;
    if (isGetter = tn.skip(Token.GET))
      modifiers = addModifier(Node.createModifier(ModifierKind.GET, tn.range()), modifiers);
    else if (isSetter = tn.skip(Token.SET)) // can't be both
      modifiers = addModifier(Node.createModifier(ModifierKind.SET, tn.range()), modifiers);

    if (tn.skip(Token.CONSTRUCTOR) || tn.skip(Token.IDENTIFIER)) { // order is important
      var identifier: IdentifierExpression = tn.token == Token.CONSTRUCTOR
        ? Node.createConstructor(tn.range())
        : Node.createIdentifier(tn.readIdentifier(), tn.range());
      var typeParameters: TypeParameter[] | null;
      if (tn.skip(Token.LESSTHAN)) {
        if (identifier.kind == NodeKind.CONSTRUCTOR)
          this.error(DiagnosticCode.Type_parameters_cannot_appear_on_a_constructor_declaration, tn.range()); // recoverable
        typeParameters = this.parseTypeParameters(tn);
        if (!typeParameters)
          return null;
      } else
        typeParameters = [];

      if (identifier.kind == NodeKind.CONSTRUCTOR && tn.peek() != Token.OPENPAREN)
        this.error(DiagnosticCode.Constructor_implementation_is_missing, tn.range());

      // method: '(' Parameters (':' Type)? '{' Statement* '}' ';'?
      if (tn.skip(Token.OPENPAREN)) {
        var parameters = this.parseParameters(tn);
        if (!parameters)
          return null;
        if (isGetter && parameters.length)
          this.error(DiagnosticCode.A_get_accessor_cannot_have_parameters, identifier.range);
        if (isSetter) {
          if (parameters.length != 1)
            this.error(DiagnosticCode.A_set_accessor_must_have_exactly_one_parameter, identifier.range);
          if (parameters.length && parameters[0].initializer)
            this.error(DiagnosticCode.A_set_accessor_parameter_cannot_have_an_initializer, identifier.range);
        }
        var returnType: TypeNode | null = null;
        if (tn.skip(Token.COLON)) {
          if (identifier.kind == NodeKind.CONSTRUCTOR)
            this.error(DiagnosticCode.Type_annotation_cannot_appear_on_a_constructor_declaration, tn.range());
          else if (isSetter)
            this.error(DiagnosticCode.A_set_accessor_cannot_have_a_return_type_annotation, tn.range());
          returnType = this.parseType(tn, identifier.kind == NodeKind.CONSTRUCTOR || isSetter);
          if (!returnType)
            return null;
        } else if (!isSetter && identifier.kind != NodeKind.CONSTRUCTOR)
          this.error(DiagnosticCode.Type_expected, tn.range()); // recoverable
        var statements: Statement[] | null = null;
        if (tn.skip(Token.OPENBRACE)) {
          if (parentIsDeclare)
            this.error(DiagnosticCode.An_implementation_cannot_be_declared_in_ambient_contexts, tn.range()); // recoverable
          statements = new Array();
          while (!tn.skip(Token.CLOSEBRACE)) {
            var statement = this.parseStatement(tn);
            if (!statement)
              return null;
            statements.push(<Statement>statement);
          }
        } else {
          if (!parentIsDeclare)
            this.error(DiagnosticCode.Function_implementation_is_missing_or_not_immediately_following_the_declaration, tn.range()); // recoverable
        }

        var retMethod = Node.createMethod(identifier, <TypeParameter[]>typeParameters, <Parameter[]>parameters, returnType, statements, modifiers, decorators, tn.range(startPos, tn.pos));
        tn.skip(Token.SEMICOLON);
        return retMethod;

      // field: (':' Type)? ('=' Expression)? ';'?
      } else {
        var modifier: Modifier | null;
        if (modifier = getModifier(ModifierKind.ABSTRACT, modifiers))
          this.error(DiagnosticCode._0_modifier_cannot_be_used_here, modifier.range, "abstract"); // recoverable
        if (modifier = getModifier(ModifierKind.GET, modifiers))
          this.error(DiagnosticCode._0_modifier_cannot_be_used_here, modifier.range, "get"); // recoverable
        if (modifier = getModifier(ModifierKind.SET, modifiers))
          this.error(DiagnosticCode._0_modifier_cannot_be_used_here, modifier.range, "set"); // recoverable
        var type: TypeNode | null = null;
        if (tn.skip(Token.COLON)) {
          type = this.parseType(tn);
          if (!type)
            return null;
        } else
          this.error(DiagnosticCode.Type_expected, tn.range()); // recoverable
        var initializer: Expression | null = null;
        if (tn.skip(Token.EQUALS)) {
          initializer = this.parseExpression(tn);
          if (!initializer)
            return null;
        }
        var retField = Node.createField(identifier, type, initializer, modifiers, decorators, tn.range(startPos, tn.pos));
        tn.skip(Token.SEMICOLON);
        return retField;
      }
    } else
      this.error(DiagnosticCode.Identifier_expected, tn.range());
    return null;
  }

  parseNamespace(tn: Tokenizer, modifiers: Modifier[] | null, decorators: Decorator[] | null): NamespaceDeclaration | null {
    // at 'namespace': Identifier '{' (Variable | Function)* '}'
    var startPos = modifiers && modifiers.length ? modifiers[0].range.start : tn.tokenPos;
    if (tn.skip(Token.IDENTIFIER)) {
      var identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
      if (tn.skip(Token.OPENBRACE)) {
        var members = new Array<Statement>();
        while (!tn.skip(Token.CLOSEBRACE)) {
          var member = this.parseTopLevelStatement(tn, true);
          if (!member)
            return null;
          members.push(member);
        }
        var ret = Node.createNamespace(identifier, members, modifiers, decorators, tn.range(startPos, tn.pos));
        tn.skip(Token.SEMICOLON);
        return ret;
      } else
        this.error(DiagnosticCode._0_expected, tn.range(), "{");
    } else
      this.error(DiagnosticCode.Identifier_expected, tn.range());
    return null;
  }

  parseExport(tn: Tokenizer, modifiers: Modifier[] | null): ExportStatement | null {
    // at 'export': '{' ExportMember (',' ExportMember)* }' ('from' StringLiteral)? ';'?
    var startPos = modifiers && modifiers.length ? modifiers[0].range.start : tn.tokenPos;
    if (tn.skip(Token.OPENBRACE)) {
      var members = new Array<ExportMember>();
      if (!tn.skip(Token.CLOSEBRACE)) {
        do {
          var member = this.parseExportMember(tn);
          if (!member)
            return null;
          members.push(member);
        } while (tn.skip(Token.COMMA));
        if (!tn.skip(Token.CLOSEBRACE)) {
          this.error(DiagnosticCode._0_expected, tn.range(), "}");
          return null;
        }
      }
      var path: StringLiteralExpression | null = null;
      if (tn.skip(Token.FROM)) {
        if (tn.skip(Token.STRINGLITERAL))
          path = Node.createStringLiteral(tn.readString(), tn.range());
        else {
          this.error(DiagnosticCode.String_literal_expected, tn.range());
          return null;
        }
      }
      var ret = Node.createExport(members, path, modifiers, tn.range(startPos, tn.pos));
      if (ret.normalizedPath && !this.seenlog.has(<string>ret.normalizedPath)) {
        this.backlog.push(<string>ret.normalizedPath);
        this.seenlog.add(<string>ret.normalizedPath);
      }
      tn.skip(Token.SEMICOLON);
      return ret;
    } else
      this.error(DiagnosticCode._0_expected, tn.range(), "{");
    return null;
  }

  parseExportMember(tn: Tokenizer): ExportMember | null {
    // Identifier ('as' Identifier)?
    if (tn.skip(Token.IDENTIFIER)) {
      var identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
      var asIdentifier: IdentifierExpression | null = null;
      if (tn.skip(Token.AS)) {
        if (tn.skip(Token.IDENTIFIER))
          asIdentifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
        else {
          this.error(DiagnosticCode.Identifier_expected, tn.range());
          return null;
        }
      }
      return Node.createExportMember(identifier, asIdentifier, asIdentifier ? Range.join(identifier.range, asIdentifier.range) : identifier.range);
    } else
      this.error(DiagnosticCode.Identifier_expected, tn.range());
    return null;
  }

  parseImport(tn: Tokenizer): ImportStatement | null {
    // at 'import': ('{' (ImportMember (',' ImportMember)*)? '}' | '*' 'as' Identifier) 'from' StringLiteral ';'?
    var startPos = tn.tokenPos;
    var members: ImportDeclaration[] | null = null;
    var namespaceName: IdentifierExpression | null = null;
    if (tn.skip(Token.OPENBRACE)) {
      members = new Array();
      if (!tn.skip(Token.CLOSEBRACE)) {
        do {
          var member = this.parseImportDeclaration(tn);
          if (!member)
            return null;
          members.push(member);
        } while (tn.skip(Token.COMMA));
        if (!tn.skip(Token.CLOSEBRACE)) {
          this.error(DiagnosticCode._0_expected, tn.range(), "}");
          return null;
        }
      }
    } else if (tn.skip(Token.ASTERISK)) {
      if (tn.skip(Token.AS)) {
        if (tn.skip(Token.IDENTIFIER)) {
          namespaceName = Node.createIdentifier(tn.readIdentifier(), tn.range());
        } else {
          this.error(DiagnosticCode.Identifier_expected, tn.range());
          return null;
        }
      } else {
        this.error(DiagnosticCode._0_expected, tn.range(), "as");
        return null;
      }
    } else {
      this.error(DiagnosticCode._0_expected, tn.range(), "{");
      return null;
    }
    if (tn.skip(Token.FROM)) {
      if (tn.skip(Token.STRINGLITERAL)) {
        var path = Node.createStringLiteral(tn.readString(), tn.range());
        var ret: ImportStatement;
        if (members) {
          if (!namespaceName)
            ret = Node.createImport(members, path, tn.range(startPos, tn.pos));
          else {
            assert(false);
            return null;
          }
        } else if (namespaceName) {
          ret = Node.createImportAll(namespaceName, path, tn.range(startPos, tn.pos));
        } else {
          assert(false);
          return null;
        }
        if (!this.seenlog.has(ret.normalizedPath)) {
          this.backlog.push(ret.normalizedPath);
          this.seenlog.add(ret.normalizedPath);
        }
        tn.skip(Token.SEMICOLON);
        return ret;
      } else
        this.error(DiagnosticCode.String_literal_expected, tn.range());
    } else
      this.error(DiagnosticCode._0_expected, tn.range(), "from");
    return null;
  }

  parseImportDeclaration(tn: Tokenizer): ImportDeclaration | null {
    // Identifier ('as' Identifier)?
    if (tn.skip(Token.IDENTIFIER)) {
      var identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
      var asIdentifier: IdentifierExpression | null = null;
      if (tn.skip(Token.AS)) {
        if (tn.skip(Token.IDENTIFIER))
          asIdentifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
        else {
          this.error(DiagnosticCode.Identifier_expected, tn.range());
          return null;
        }
      }
      return Node.createImportDeclaration(identifier, asIdentifier, asIdentifier ? Range.join(identifier.range, asIdentifier.range) : identifier.range);
    } else
      this.error(DiagnosticCode.Identifier_expected, tn.range());
    return null;
  }

  parseExportImport(tn: Tokenizer, startRange: Range): ExportImportStatement | null {
    // at 'export' 'import': Identifier ('=' Identifier)? ';'?
    if (tn.skip(Token.IDENTIFIER)) {
      var asIdentifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
      if (tn.skip(Token.EQUALS)) {
        if (tn.skip(Token.IDENTIFIER)) {
          var identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
          var ret = Node.createExportImport(identifier, asIdentifier, Range.join(startRange, tn.range()));
          tn.skip(Token.SEMICOLON);
          return ret;
        } else
          this.error(DiagnosticCode.Identifier_expected, tn.range());
      } else
        this.error(DiagnosticCode._0_expected, tn.range(), "=");
    } else
      this.error(DiagnosticCode.Identifier_expected, tn.range());
    return null;
  }

  parseStatement(tn: Tokenizer, topLevel: bool = false): Statement | null {
    // at previous token
    tn.mark();
    var token = tn.next();
    switch (token) {

      case Token.BREAK:
        return this.parseBreak(tn);

      case Token.CONST:
        return this.parseVariable(tn, [ Node.createModifier(ModifierKind.CONST, tn.range()) ], null);

      case Token.CONTINUE:
        return this.parseContinue(tn);

      case Token.DO:
        return this.parseDoStatement(tn);

      case Token.FOR:
        return this.parseForStatement(tn);

      case Token.IF:
        return this.parseIfStatement(tn);

      case Token.LET:
      case Token.VAR:
        return this.parseVariable(tn, null, null);

      case Token.OPENBRACE:
        return this.parseBlockStatement(tn, topLevel);

      case Token.RETURN:
        if (topLevel)
          this.error(DiagnosticCode.A_return_statement_can_only_be_used_within_a_function_body, tn.range()); // recoverable
        return this.parseReturn(tn);

      case Token.SEMICOLON:
        return Node.createEmpty(tn.range(tn.tokenPos));

      case Token.SWITCH:
        return this.parseSwitchStatement(tn);

      case Token.THROW:
        return this.parseThrowStatement(tn);

      case Token.TRY:
        return this.parseTryStatement(tn);

      case Token.TYPE:
        return this.parseTypeDeclaration(tn, null);

      case Token.WHILE:
        return this.parseWhileStatement(tn);

      default:
        tn.reset();
        return this.parseExpressionStatement(tn);
    }
  }

  parseBlockStatement(tn: Tokenizer, topLevel: bool): BlockStatement | null {
    // at '{': Statement* '}' ';'?
    var startPos = tn.tokenPos;
    var statements = new Array<Statement>();
    while (!tn.skip(Token.CLOSEBRACE)) {
      var statement = this.parseStatement(tn, topLevel);
      if (!statement)
        return null;
      statements.push(statement);
    }
    var ret = Node.createBlock(statements, tn.range(startPos, tn.pos));
    tn.skip(Token.SEMICOLON);
    return ret;
  }

  parseBreak(tn: Tokenizer): BreakStatement | null {
    // at 'break': Identifier? ';'?
    var identifier: IdentifierExpression | null = null;
    if (tn.peek(true) == Token.IDENTIFIER && !tn.nextTokenOnNewLine) {
      tn.next(true);
      identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
    }
    var ret = Node.createBreak(identifier, tn.range());
    tn.skip(Token.SEMICOLON);
    return ret;
  }

  parseContinue(tn: Tokenizer): ContinueStatement | null {
    // at 'continue': Identifier? ';'?
    var identifier: IdentifierExpression | null = null;
    if (tn.peek(true) == Token.IDENTIFIER && !tn.nextTokenOnNewLine) {
      tn.next(true);
      identifier = Node.createIdentifier(tn.readIdentifier(), tn.range());
    }
    var ret = Node.createContinue(identifier, tn.range());
    tn.skip(Token.SEMICOLON);
    return ret;
  }

  parseDoStatement(tn: Tokenizer): DoStatement | null {
    // at 'do': Statement 'while' '(' Expression ')' ';'?
    var startPos = tn.tokenPos;
    var statement = this.parseStatement(tn);
    if (!statement)
      return null;
    if (tn.skip(Token.WHILE)) {
      if (tn.skip(Token.OPENPAREN)) {
        var condition = this.parseExpression(tn);
        if (!condition)
          return null;
        if (tn.skip(Token.CLOSEPAREN)) {
          var ret = Node.createDo(<Statement>statement, <Expression>condition, tn.range(startPos, tn.pos));
          tn.skip(Token.SEMICOLON);
          return ret;
        }
        this.error(DiagnosticCode._0_expected, tn.range(), ")");
      } else
        this.error(DiagnosticCode._0_expected, tn.range(), "(");
    } else
      this.error(DiagnosticCode._0_expected, tn.range(), "while");
    return null;
  }

  parseExpressionStatement(tn: Tokenizer): ExpressionStatement | null {
    // at previous token
    var expr = this.parseExpression(tn);
    if (!expr)
      return null;
    var ret = Node.createExpression(expr);
    tn.skip(Token.SEMICOLON);
    return ret;
  }

  parseForStatement(tn: Tokenizer): ForStatement | null {
    // at 'for': '(' Statement? Expression? ';' Expression? ')' Statement
    var startPos = tn.tokenPos;
    if (tn.skip(Token.OPENPAREN)) {
      var initializer: Statement | null = null;
      if (tn.skip(Token.LET) || tn.skip(Token.CONST) || tn.skip(Token.VAR)) {
        initializer = this.parseVariable(tn, null, null);
      } else if (!tn.skip(Token.SEMICOLON)) {
        initializer = this.parseExpressionStatement(tn);
        if (!initializer)
          return null;
      }
      if (tn.token == Token.SEMICOLON) {
        var condition: ExpressionStatement | null = null;
        if (!tn.skip(Token.SEMICOLON)) {
          condition = this.parseExpressionStatement(tn);
          if (!condition)
            return null;
        }
        if (tn.token == Token.SEMICOLON) {
          var incrementor: Expression | null = null;
          if (!tn.skip(Token.CLOSEPAREN)) {
            incrementor = this.parseExpression(tn);
            if (!incrementor)
              return null;
            if (!tn.skip(Token.CLOSEPAREN)) {
              this.error(DiagnosticCode._0_expected, tn.range(), ")");
              return null;
            }
          }
          var statement = this.parseStatement(tn);
          if (!statement)
            return null;
          return Node.createFor(initializer, condition ? condition.expression : null, incrementor, statement, tn.range(startPos, tn.pos));
        } else
          this.error(DiagnosticCode._0_expected, tn.range(), ";");
      } else
        this.error(DiagnosticCode._0_expected, tn.range(), ";");
    } else
      this.error(DiagnosticCode._0_expected, tn.range(), "(");
    return null;
  }

  parseIfStatement(tn: Tokenizer): IfStatement | null {
    // at 'if': '(' Expression ')' Statement ('else' Statement)?
    var startPos = tn.tokenPos;
    if (tn.skip(Token.OPENPAREN)) {
      var condition = this.parseExpression(tn);
      if (!condition)
        return null;
      if (tn.skip(Token.CLOSEPAREN)) {
        var statement = this.parseStatement(tn);
        if (!statement)
          return null;
        var elseStatement: Statement | null = null;
        if (tn.skip(Token.ELSE)) {
          elseStatement = this.parseStatement(tn);
          if (!elseStatement)
            return null;
        }
        return Node.createIf(<Expression>condition, <Statement>statement, elseStatement, tn.range(startPos, tn.pos));
      }
      this.error(DiagnosticCode._0_expected, tn.range(), ")");
    } else
      this.error(DiagnosticCode._0_expected, tn.range(), "(");
    return null;
  }

  parseSwitchStatement(tn: Tokenizer): SwitchStatement | null {
    // at 'switch': '(' Expression ')' '{' SwitchCase* '}' ';'?
    var startPos = tn.tokenPos;
    if (tn.skip(Token.OPENPAREN)) {
      var condition = this.parseExpression(tn);
      if (!condition)
        return null;
      if (tn.skip(Token.CLOSEPAREN)) {
        if (tn.skip(Token.OPENBRACE)) {
          var cases = new Array<SwitchCase>();
          while (!tn.skip(Token.CLOSEBRACE)) {
            var case_ = this.parseSwitchCase(tn);
            if (!case_)
              return null;
            cases.push(<SwitchCase>case_);
          }
          var ret = Node.createSwitch(condition, cases, tn.range(startPos, tn.pos));
          tn.skip(Token.SEMICOLON);
          return ret;
        } else
          this.error(DiagnosticCode._0_expected, tn.range(), "{");
      } else
        this.error(DiagnosticCode._0_expected, tn.range(), ")");
    } else
      this.error(DiagnosticCode._0_expected, tn.range(), "(");
    return null;
  }

  parseSwitchCase(tn: Tokenizer): SwitchCase | null {
    var startPos = tn.tokenPos;
    var statements: Statement[],
        statement: Statement | null;

    // 'case' Expression ':' Statement*
    if (tn.skip(Token.CASE)) {
      var label = this.parseExpression(tn);
      if (!label)
        return null;
      if (tn.skip(Token.COLON)) {
        statements = new Array<Statement>();
        while (tn.peek() != Token.CASE && tn.nextToken != Token.DEFAULT && tn.nextToken != Token.CLOSEBRACE) {
          statement = this.parseStatement(tn);
          if (!statement)
            return null;
          statements.push(<Statement>statement);
        }
        return Node.createSwitchCase(<Expression>label, statements, tn.range(startPos, tn.pos));
      } else
        this.error(DiagnosticCode._0_expected, tn.range(), ":");

    // 'default' ':' Statement*
    } else if (tn.skip(Token.DEFAULT)) {
      if (tn.skip(Token.COLON)) {
        statements = new Array<Statement>();
        while (tn.peek() != Token.CASE && tn.nextToken != Token.DEFAULT && tn.nextToken != Token.CLOSEBRACE) {
          statement = this.parseStatement(tn);
          if (!statement)
            return null;
          statements.push(statement);
        }
        return Node.createSwitchCase(null, statements, tn.range(startPos, tn.pos));
      } else
        this.error(DiagnosticCode._0_expected, tn.range(), ":");

    } else
      this.error(DiagnosticCode._case_or_default_expected, tn.range());

    return null;
  }

  parseThrowStatement(tn: Tokenizer): ThrowStatement | null {
    // at 'throw': Expression ';'?
    var startPos = tn.tokenPos;
    var expression = this.parseExpression(tn);
    if (!expression)
      return null;
    var ret = Node.createThrow(<Expression>expression, tn.range(startPos, tn.pos));
    tn.skip(Token.SEMICOLON);
    return ret;
  }

  parseTryStatement(tn: Tokenizer): TryStatement | null {
    // at 'try': '{' Statement* '}' ('catch' '(' VariableMember ')' '{' Statement* '}')? ('finally' '{' Statement* '}'? ';'?
    var startPos = tn.tokenPos;
    var stmt: Statement | null;
    if (tn.skip(Token.OPENBRACE)) {
      var statements = new Array<Statement>();
      while (!tn.skip(Token.CLOSEBRACE)) {
        stmt = this.parseStatement(tn);
        if (!stmt)
          return null;
        statements.push(<Statement>stmt);
      }
      var catchVariable: IdentifierExpression | null = null;
      var catchStatements: Statement[] | null = null;
      var finallyStatements: Statement[] | null = null;
      if (tn.skip(Token.CATCH)) {
        if (!tn.skip(Token.OPENPAREN)) {
          this.error(DiagnosticCode._0_expected, tn.range(), "(");
          return null;
        }
        if (!tn.skip(Token.IDENTIFIER)) {
          this.error(DiagnosticCode.Identifier_expected, tn.range());
          return null;
        }
        catchVariable = Node.createIdentifier(tn.readIdentifier(), tn.range());
        if (!tn.skip(Token.CLOSEPAREN)) {
          this.error(DiagnosticCode._0_expected, tn.range(), ")");
          return null;
        }
        if (!tn.skip(Token.OPENBRACE)) {
          this.error(DiagnosticCode._0_expected, tn.range(), "{");
          return null;
        }
        catchStatements = new Array();
        while (!tn.skip(Token.CLOSEBRACE)) {
          var stmt = this.parseStatement(tn);
          if (!stmt)
            return null;
          catchStatements.push(<Statement>stmt);
        }
      }
      if (tn.skip(Token.FINALLY)) {
        if (!tn.skip(Token.OPENBRACE)) {
          this.error(DiagnosticCode._0_expected, tn.range(), "{");
          return null;
        }
        finallyStatements = new Array();
        while (!tn.skip(Token.CLOSEBRACE)) {
          stmt = this.parseStatement(tn);
          if (!stmt)
            return null;
          finallyStatements.push(<Statement>stmt);
        }
      }
      if (!(catchStatements || finallyStatements)) {
        this.error(DiagnosticCode._0_expected, tn.range(), "catch");
        return null;
      }
      var ret = Node.createTry(statements, catchVariable, catchStatements, finallyStatements, tn.range(startPos, tn.pos));
      tn.skip(Token.SEMICOLON);
      return ret;
    } else
      this.error(DiagnosticCode._0_expected, tn.range(), "{");
    return null;
  }

  parseTypeDeclaration(tn: Tokenizer, modifiers: Modifier[] | null = null, decorators: Decorator[] | null = null): TypeDeclaration | null {
    // at 'type': Identifier '=' Type ';'?
    var startPos = decorators && decorators.length ? decorators[0].range.start
                 : modifiers && modifiers.length ? modifiers[0].range.start
                 : tn.tokenPos;
    if (tn.skip(Token.IDENTIFIER)) {
      var name = Node.createIdentifier(tn.readIdentifier(), tn.range());
      if (tn.skip(Token.EQUALS)) {
        var type = this.parseType(tn);
        if (!type)
          return null;
        var ret = Node.createTypeDeclaration(name, type, modifiers, decorators, tn.range(startPos, tn.pos));
        tn.skip(Token.SEMICOLON);
        return ret;
      } else
        this.error(DiagnosticCode._0_expected, tn.range(), "=");
    } else
      this.error(DiagnosticCode.Identifier_expected, tn.range());
    return null;
  }

  parseWhileStatement(tn: Tokenizer): WhileStatement | null {
    // at 'while': '(' Expression ')' Statement ';'?
    var startPos = tn.tokenPos;
    if (tn.skip(Token.OPENPAREN)) {
      var expression = this.parseExpression(tn);
      if (!expression)
        return null;
      if (tn.skip(Token.CLOSEPAREN)) {
        var statement = this.parseStatement(tn);
        if (!statement)
          return null;
        var ret = Node.createWhile(<Expression>expression, <Statement>statement, tn.range(startPos, tn.pos));
        tn.skip(Token.SEMICOLON);
        return ret;
      } else
        this.error(DiagnosticCode._0_expected, tn.range(), ")");
    } else
      this.error(DiagnosticCode._0_expected, tn.range(), "(");
    return null;
  }

  // expressions
  // see: http://www.engr.mun.ca/~theo/Misc/exp_parsing.htm#climbing

  parseExpressionStart(tn: Tokenizer): Expression | null {
    var token = tn.next(true);
    var startPos = tn.tokenPos;
    var expr: Expression | null = null;

    if (token == Token.NULL)
      return Node.createNull(tn.range());
    if (token == Token.TRUE)
      return Node.createTrue(tn.range());
    if (token == Token.FALSE)
      return Node.createFalse(tn.range());

    var p = determinePrecedenceStart(token);
    if (p != Precedence.INVALID) {
      var operand: Expression | null;

      // TODO: SpreadExpression, YieldExpression (currently become unsupported UnaryPrefixExpressions)

      // NewExpression
      if (token == Token.NEW) {
        operand = this.parseExpression(tn, Precedence.CALL);
        if (!operand)
          return null;
        if (operand.kind == NodeKind.CALL)
          return Node.createNew((<CallExpression>operand).expression, (<CallExpression>operand).typeArguments, (<CallExpression>operand).arguments, tn.range(startPos, tn.pos));
        this.error(DiagnosticCode.Operation_not_supported, tn.range());
        return null;
      } else
        operand = this.parseExpression(tn, p);

      // UnaryPrefixExpression
      if (token == Token.PLUS_PLUS || token == Token.MINUS_MINUS)
        if ((<Expression>operand).kind != NodeKind.IDENTIFIER && (<Expression>operand).kind != NodeKind.ELEMENTACCESS && (<Expression>operand).kind != NodeKind.PROPERTYACCESS)
          this.error(DiagnosticCode.The_operand_of_an_increment_or_decrement_operator_must_be_a_variable_or_a_property_access, (<Expression>operand).range);
      return Node.createUnaryPrefix(token, <Expression>operand, tn.range(startPos, tn.pos));
    }

    switch (token) {

      // ParenthesizedExpression
      case Token.OPENPAREN: {
        expr = this.parseExpression(tn);
        if (!expr)
          return null;
        if (!tn.skip(Token.CLOSEPAREN)) {
          this.error(DiagnosticCode._0_expected, tn.range(), ")");
          return null;
        }
        return Node.createParenthesized(expr, tn.range(startPos, tn.pos));
      }

      // ArrayLiteralExpression
      case Token.OPENBRACKET: {
        var elementExpressions = new Array<Expression | null>();
        if (!tn.skip(Token.CLOSEBRACKET)) {
          do {
            if (tn.peek() == Token.COMMA || tn.peek() == Token.CLOSEBRACKET)
              expr = null; // omitted
            else {
              expr = this.parseExpression(tn, Precedence.COMMA + 1);
              if (!expr)
                return null;
            }
            elementExpressions.push(expr);
          } while (tn.skip(Token.COMMA));
          if (!tn.skip(Token.CLOSEBRACKET)) {
            this.error(DiagnosticCode._0_expected, tn.range(), "]");
            return null;
          }
        }
        return Node.createArrayLiteral(elementExpressions, tn.range(startPos, tn.pos));
      }

      // AssertionExpression (unary prefix)
      case Token.LESSTHAN: {
        var toType = this.parseType(tn);
        if (!toType)
          return null;
        if (!tn.skip(Token.GREATERTHAN)) {
          this.error(DiagnosticCode._0_expected, tn.range(), ">");
          return null;
        }
        expr = this.parseExpression(tn, Precedence.CALL);
        if (!expr)
          return null;
        return Node.createAssertion(AssertionKind.PREFIX, <Expression>expr, <TypeNode>toType, tn.range(startPos, tn.pos));
      }

      // IdentifierExpression
      case Token.IDENTIFIER:
        return Node.createIdentifier(tn.readIdentifier(), tn.range(startPos, tn.pos));

      case Token.THIS:
        return Node.createThis(tn.range(startPos, tn.pos));

      case Token.CONSTRUCTOR:
        return Node.createConstructor(tn.range(startPos, tn.pos));

      case Token.SUPER:
        return Node.createSuper(tn.range(startPos, tn.pos));

      // StringLiteralExpression
      case Token.STRINGLITERAL:
        return Node.createStringLiteral(tn.readString(), tn.range(startPos, tn.pos));

      // IntegerLiteralExpression
      case Token.INTEGERLITERAL:
        return Node.createIntegerLiteral(tn.readInteger(), tn.range(startPos, tn.pos));

      // FloatLiteralExpression
      case Token.FLOATLITERAL:
        return Node.createFloatLiteral(tn.readFloat(), tn.range(startPos, tn.pos));

      // RegexpLiteralExpression
      case Token.REGEXPLITERAL:
        return Node.createRegexpLiteral(tn.readRegexp(), tn.range(startPos, tn.pos));

      default:
        this.error(DiagnosticCode.Expression_expected, tn.range());
        return null;
    }
  }

  tryParseTypeArgumentsBeforeArguments(tn: Tokenizer): TypeNode[] | null {
    // at '<': Identifier (',' Identifier)* '>' '('
    tn.mark();
    if (!tn.skip(Token.LESSTHAN))
      return null;

    var typeArguments = new Array<TypeNode>();
    do {
      var type = this.parseType(tn, true, true);
      if (!type) {
        tn.reset();
        return null;
      }
      typeArguments.push(type);
    } while (tn.skip(Token.COMMA));
    if (!(tn.skip(Token.GREATERTHAN) && tn.skip(Token.OPENPAREN))) {
      tn.reset();
      return null;
    }
    return typeArguments;
  }

  parseArguments(tn: Tokenizer): Expression[] | null {
    // at '(': (Expression (',' Expression)*)? ')'
    var args = new Array<Expression>();
    if (!tn.skip(Token.CLOSEPAREN)) {
      do {
        var expr = this.parseExpression(tn, Precedence.COMMA + 1);
        if (!expr)
          return null;
        args.push(<Expression>expr);
      } while (tn.skip(Token.COMMA));
      if (!tn.skip(Token.CLOSEPAREN)) {
        this.error(DiagnosticCode._0_expected, tn.range(), ")");
        return null;
      }
    }
    return args;
  }

  parseExpression(tn: Tokenizer, precedence: Precedence = 0): Expression | null {
    var expr = this.parseExpressionStart(tn);
    if (!expr)
      return null;

    var startPos = expr.range.start;

    // CallExpression
    var typeArguments = this.tryParseTypeArgumentsBeforeArguments(tn);
    // there might be better ways to distinguish a LESSTHAN from a CALL with type arguments
    if (typeArguments || tn.skip(Token.OPENPAREN)) {
      var args = this.parseArguments(tn);
      if (!args)
        return null;
      expr = Node.createCall(expr, <TypeNode[]>(typeArguments ? typeArguments : []), args, tn.range(startPos, tn.pos));
    }

    var token: Token;
    var next: Expression | null = null;
    var nextPrecedence: Precedence;

    while ((nextPrecedence = determinePrecedence(token = tn.peek())) >= precedence) { // precedence climbing
      tn.next();

      // AssertionExpression
      if (token == Token.AS) {
        var toType = this.parseType(tn);
        if (!toType)
          return null;
        expr = Node.createAssertion(AssertionKind.AS, expr, toType, tn.range(startPos, tn.pos));

      // ElementAccessExpression
      } else if (token == Token.OPENBRACKET) {
        next = this.parseExpression(tn); // resets precedence
        if (!next)
          return null;

        if (tn.skip(Token.CLOSEBRACKET))
          expr = Node.createElementAccess(<Expression>expr, <Expression>next, tn.range(startPos, tn.pos));
        else {
          this.error(DiagnosticCode._0_expected, tn.range(), "]");
          return null;
        }

      // UnaryPostfixExpression
      } else if (token == Token.PLUS_PLUS || token == Token.MINUS_MINUS) {
        if (expr.kind != NodeKind.IDENTIFIER && expr.kind != NodeKind.ELEMENTACCESS && expr.kind != NodeKind.PROPERTYACCESS)
          this.error(DiagnosticCode.The_operand_of_an_increment_or_decrement_operator_must_be_a_variable_or_a_property_access, expr.range);
        expr = Node.createUnaryPostfix(token, expr, tn.range(startPos, tn.pos));

      // TernaryExpression
      } else if (token == Token.QUESTION) {
        var ifThen = this.parseExpression(tn);
        if (!ifThen)
          return null;
        if (tn.skip(Token.COLON)) {
          var ifElse = this.parseExpression(tn);
          if (!ifElse)
            return null;
          expr = Node.createTernary(<Expression>expr, <Expression>ifThen, <Expression>ifElse, tn.range(startPos, tn.pos));
        } else {
          this.error(DiagnosticCode._0_expected, tn.range(), ":");
          return null;
        }

      } else {
        next = this.parseExpression(tn, isRightAssociative(token) ? nextPrecedence : 1 + nextPrecedence);
        if (!next)
          return null;

        // PropertyAccessExpression
        if (token == Token.DOT) {
          if (next.kind == NodeKind.IDENTIFIER) {
            expr = Node.createPropertyAccess(<Expression>expr, <IdentifierExpression>next, tn.range(startPos, tn.pos));
          } else if (next.kind == NodeKind.CALL) { // amend
            var propertyCall = <CallExpression>next;
            if (propertyCall.expression.kind == NodeKind.IDENTIFIER) {
              propertyCall.expression = Node.createPropertyAccess(<Expression>expr, <IdentifierExpression>propertyCall.expression, tn.range(startPos, tn.pos));
            } else
              throw new Error("unexpected expression kind");
            expr = propertyCall;
          } else {
            this.error(DiagnosticCode.Identifier_expected, next.range);
            return null;
          }

        // BinaryExpression
        } else
          expr = Node.createBinary(token, <Expression>expr, <Expression>next, tn.range(startPos, tn.pos));
      }
    }
    return expr;
  }
}

/** Operator precedence from least to largest. */
export const enum Precedence {
  COMMA,
  SPREAD,
  YIELD,
  ASSIGNMENT,
  CONDITIONAL,
  LOGICAL_OR,
  LOGICAL_AND,
  BITWISE_OR,
  BITWISE_XOR,
  BITWISE_AND,
  EQUALITY,
  RELATIONAL,
  SHIFT,
  ADDITIVE,
  MULTIPLICATIVE,
  EXPONENTIATED,
  UNARY_PREFIX,
  UNARY_POSTFIX,
  CALL,
  MEMBERACCESS,
  GROUPING,
  INVALID = -1
}

/** Determines the precedence of a starting token. */
function determinePrecedenceStart(kind: Token): i32 {
  switch (kind) {

    case Token.DOT_DOT_DOT:
      return Precedence.SPREAD;

    case Token.YIELD:
      return Precedence.YIELD;

    case Token.EXCLAMATION:
    case Token.TILDE:
    case Token.PLUS:
    case Token.MINUS:
    case Token.PLUS_PLUS:
    case Token.MINUS_MINUS:
    case Token.TYPEOF:
    case Token.VOID:
    case Token.DELETE:
      return Precedence.UNARY_PREFIX;

    case Token.NEW:
      return Precedence.MEMBERACCESS;

    default:
      return Precedence.INVALID;
  }
}

/** Determines the precende of a non-starting token. */
function determinePrecedence(kind: Token): i32 {
  switch (kind) {

    case Token.COMMA:
      return Precedence.COMMA;

    case Token.EQUALS:
    case Token.PLUS_EQUALS:
    case Token.MINUS_EQUALS:
    case Token.ASTERISK_ASTERISK_EQUALS:
    case Token.ASTERISK_EQUALS:
    case Token.SLASH_EQUALS:
    case Token.PERCENT_EQUALS:
    case Token.LESSTHAN_LESSTHAN_EQUALS:
    case Token.GREATERTHAN_GREATERTHAN_EQUALS:
    case Token.GREATERTHAN_GREATERTHAN_GREATERTHAN_EQUALS:
    case Token.AMPERSAND_EQUALS:
    case Token.CARET_EQUALS:
    case Token.BAR_EQUALS:
      return Precedence.ASSIGNMENT;

    case Token.QUESTION:
      return Precedence.CONDITIONAL;

    case Token.BAR_BAR:
      return Precedence.LOGICAL_OR;

    case Token.AMPERSAND_AMPERSAND:
      return Precedence.LOGICAL_AND;

    case Token.BAR:
      return Precedence.BITWISE_OR;

    case Token.CARET:
      return Precedence.BITWISE_XOR;

    case Token.AMPERSAND:
      return Precedence.BITWISE_AND;

    case Token.EQUALS_EQUALS:
    case Token.EXCLAMATION_EQUALS:
    case Token.EQUALS_EQUALS_EQUALS:
    case Token.EXCLAMATION_EQUALS_EQUALS:
      return Precedence.EQUALITY;

    case Token.AS:
    case Token.IN:
    case Token.INSTANCEOF:
    case Token.LESSTHAN:
    case Token.GREATERTHAN:
    case Token.LESSTHAN_EQUALS:
    case Token.GREATERTHAN_EQUALS:
      return Precedence.RELATIONAL;

    case Token.LESSTHAN_LESSTHAN:
    case Token.GREATERTHAN_GREATERTHAN:
    case Token.GREATERTHAN_GREATERTHAN_GREATERTHAN:
      return Precedence.SHIFT;

    case Token.PLUS:
    case Token.MINUS:
      return Precedence.ADDITIVE;

    case Token.ASTERISK:
    case Token.SLASH:
    case Token.PERCENT:
      return Precedence.MULTIPLICATIVE;

    case Token.ASTERISK_ASTERISK:
      return Precedence.EXPONENTIATED;

    case Token.PLUS_PLUS:
    case Token.MINUS_MINUS:
      return Precedence.UNARY_POSTFIX;

    case Token.DOT:
    case Token.NEW:
      return Precedence.MEMBERACCESS;

    default:
      return Precedence.INVALID;
  }
}

/** Determines whether a non-starting token is right associative. */
function isRightAssociative(kind: Token): bool {
  switch (kind) {

    case Token.EQUALS:
    case Token.PLUS_EQUALS:
    case Token.MINUS_EQUALS:
    case Token.ASTERISK_ASTERISK_EQUALS:
    case Token.ASTERISK_EQUALS:
    case Token.SLASH_EQUALS:
    case Token.PERCENT_EQUALS:
    case Token.LESSTHAN_LESSTHAN_EQUALS:
    case Token.GREATERTHAN_GREATERTHAN_EQUALS:
    case Token.GREATERTHAN_GREATERTHAN_GREATERTHAN_EQUALS:
    case Token.AMPERSAND_EQUALS:
    case Token.CARET_EQUALS:
    case Token.BAR_EQUALS:
    case Token.QUESTION:
    case Token.ASTERISK_ASTERISK:
      return true;

    default:
      return false;
  }
}