Exemplo n.º 1
0
	def __init__(self, source, destination):
		self.src = source
		self.dst = destination
		self.writer = VMWriter(destination)
		self.iter = Lookahead(tokenizor.newTokenizor(self.src))
		self._symbol_table = SymbolTable()
Exemplo n.º 2
0
 def __init__(self, source, destination):
     self.src = source
     self.dst = destination
     self.writer = VMWriter(destination)
     self.iter = Lookahead(tokenizor.newTokenizor(self.src))
     self._symbol_table = SymbolTable()
Exemplo n.º 3
0
class CompilationEngine:
	def __init__(self, source, destination):
		self.src = source
		self.dst = destination
		self.writer = VMWriter(destination)
		self.iter = Lookahead(tokenizor.newTokenizor(self.src))
		self._symbol_table = SymbolTable()

	def compile(self):
		root = self._compileClass()
		return root

	def _compileClass(self):
		classE = Element(ELEMENTS.CLASS)
		self._readKeyword(classE, ELEMENTS.CLASS)
		self.className = self._readIdentifier(classE)
		self._readSymbol(classE, _SYMBOLS.BRACKET_CURLY_OPEN)
		self._compileClassVarDec(classE)
		self._compileSubroutine(classE)
		self._readSymbol(classE, _SYMBOLS.BRACKET_CURLY_CLOSE)
		return classE

	def _compileClassVarDec(self, parent):
		while self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _CLASSVARDEC.FIELD_TYPES:
			classVarDecE = Element(ELEMENTS.CLASSVARDEC)
			self._readKeyword(classVarDecE)
			self._readType(classVarDecE)
			self._readIdentifier(classVarDecE)
			while self._readSymbolOptional(classVarDecE, _SYMBOLS.COMMA):
				self._readIdentifier(classVarDecE)
			self._readSymbol(classVarDecE, _SYMBOLS.SEMI_COLON)
			parent.append(classVarDecE)

	def _compileSubroutine(self, parent):
		while self.nextTok and self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _SUBROUTINEDEC.TYPES:
			subroutineDecE = Element(ELEMENTS.SUBROUTINEDEC)
			function_type = self._readKeyword(subroutineDecE)
			self._readReturnType(subroutineDecE)
			self.methodName = self._readIdentifier(subroutineDecE)
			self._symbol_table.startSubroutine(self.className, self.methodName)
			if function_type == _SUBROUTINEDEC.METHOD:
				self._symbol_table.define("this", self.className, SYM_KINDS.ARG)
			self._uid = -1
			self._readSymbol(subroutineDecE, _SYMBOLS.PARENTHESES_OPEN)
			self._compileParameters(subroutineDecE)
			self._readSymbol(subroutineDecE, _SYMBOLS.PARENTHESES_CLOSE)
			self._compileSubroutineBody(subroutineDecE, function_type)
			parent.append(subroutineDecE)

	def _gen_label(self, type_):
		self._uid += 1
		return "%s.%s.%s.%d" % (self.className, self.methodName, type_, self._uid)

	def _gen_labels(self, *parts):
		self._uid += 1
		return ["%s.%s.%s.%d" % (self.className, self.methodName, part, self._uid) for part in parts]

	def _compileSubroutineBody(self, parent, function_type):
		bodyE = Element(ELEMENTS.SUBROUTINEBODY)
		self._readSymbol(bodyE, _SYMBOLS.BRACKET_CURLY_OPEN)
		nArgs = self._compileVarDec(bodyE)
		function_name = parent[2].text
		function_full_name = "%s.%s" % (self.className, function_name)
		self.writer.writeFunction(function_full_name, nArgs)
		if function_type == _SUBROUTINEDEC.CONSTRUCTOR:
			field_count = self._symbol_table.varCount(SYM_KINDS.FIELD)
			self.writer.writePush(SEGMENT.CONST, field_count)
			self.writer.writeCall("Memory.alloc", 1)
			self.writer.writePop(SEGMENT.POINTER, 0)
		elif function_type == _SUBROUTINEDEC.METHOD:
			self.writer.writePush(SEGMENT.ARG, 0)
			self.writer.writePop(SEGMENT.POINTER, 0)
		self._compileStatements(bodyE)
		self._readSymbol(bodyE, _SYMBOLS.BRACKET_CURLY_CLOSE)
		parent.append(bodyE)

	def _compileStatements(self, parent):
		statementsE = Element(ELEMENTS.STATEMENTS)
		while self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _STATEMENTS.TYPE_NAMES:
			if self.nextTok.value == _STATEMENTS.LET:
				statementE = Element(ELEMENTS.STATEMENT_LET)
				self._readKeyword(statementE)
				identifier = self._readIdentifier(statementE)
				is_array = False
				if self._readSymbolOptional(statementE, _SYMBOLS.BRACKET_OPEN):
					is_array = True
					self._compileExpression(statementE)
					self.writer.writePush(*self._identifier_data(identifier))
					self.writer.writeArithmetic("add")
					self._readSymbol(statementE, _SYMBOLS.BRACKET_CLOSE)
				self._readSymbol(statementE, _SYMBOLS.EQUAL)
				self._compileExpression(statementE)
				self._readSymbol(statementE, _SYMBOLS.SEMI_COLON)
				if is_array:
					self.writer.writePop(SEGMENT.TEMP, 0)
					self.writer.writePop(SEGMENT.POINTER, 1)
					self.writer.writePush(SEGMENT.TEMP, 0)
					self.writer.writePop(SEGMENT.THAT, 0)
				else:
					self.writer.writePop(*self._identifier_data(identifier))
				statementsE.append(statementE)
			elif self.nextTok.value == _STATEMENTS.IF:
				label_else, label_end = self._gen_labels("if.else", "if.end")
				statementE = Element(ELEMENTS.STATEMENT_IF)
				self._readKeyword(statementE)
				self._readSymbol(statementE, _SYMBOLS.PARENTHESES_OPEN)
				self._compileExpression(statementE)
				self._readSymbol(statementE, _SYMBOLS.PARENTHESES_CLOSE)
				self.writer.writeArithmetic("not")
				self.writer.writeIf(label_else)
				self._readSymbol(statementE, _SYMBOLS.BRACKET_CURLY_OPEN)
				self._compileStatements(statementE)
				self._readSymbol(statementE, _SYMBOLS.BRACKET_CURLY_CLOSE)
				self.writer.writeGoto(label_end)
				self.writer.writeLabel(label_else)
				if self._readKeywordOptional(statementE, _KEYWORDS.ELSE):
					self._readSymbol(statementE, _SYMBOLS.BRACKET_CURLY_OPEN)
					self._compileStatements(statementE)
					self._readSymbol(statementE, _SYMBOLS.BRACKET_CURLY_CLOSE)
				self.writer.writeLabel(label_end)
				statementsE.append(statementE)
			elif self.nextTok.value == _STATEMENTS.WHILE:
				label_start, label_end = self._gen_labels("while.start", "while.end")
				self.writer.writeLabel(label_start)
				statementE = Element(ELEMENTS.STATEMENT_WHILE)
				self._readKeyword(statementE)
				self._readSymbol(statementE, _SYMBOLS.PARENTHESES_OPEN)
				self._compileExpression(statementE)
				self._readSymbol(statementE, _SYMBOLS.PARENTHESES_CLOSE)
				self.writer.writeArithmetic("not")
				self.writer.writeIf(label_end)
				self._readSymbol(statementE, _SYMBOLS.BRACKET_CURLY_OPEN)
				self._compileStatements(statementE)
				self._readSymbol(statementE, _SYMBOLS.BRACKET_CURLY_CLOSE)
				statementsE.append(statementE)
				self.writer.writeGoto(label_start)
				self.writer.writeLabel(label_end)
			elif self.nextTok.value == _STATEMENTS.DO:
				self._compileDo(statementsE)
			elif self.nextTok.value == _STATEMENTS.RETURN:
				statementE = Element(ELEMENTS.STATEMENT_RETURN)
				self._readKeyword(statementE)
				if not (self.nextTok.type == tokenizor.SYMBOL and self.nextTok.value == _SYMBOLS.SEMI_COLON):
					self._compileExpression(statementE)
				else:
					self.writer.writePush(SEGMENT.CONST, 0)
				self._readSymbol(statementE, _SYMBOLS.SEMI_COLON)
				self.writer.writeReturn()
				statementsE.append(statementE)
		if len(statementsE) == 0:
			statementsE.text = "\n"
		parent.append(statementsE)

	def _compileExpression(self, parent):
		expressionE = Element(ELEMENTS.EXPRESSION)
		self._readTerm(expressionE)
		while self.nextTok.type == tokenizor.SYMBOL and self.nextTok.value in _SYMBOLS.OPERATORS:
			symbol = self._readSymbol(expressionE)
			self._readTerm(expressionE)
			self.writer.writeArithmetic(symbol)
		parent.append(expressionE)

	def _compileExpressionList(self, parent):
		self._readSymbol(parent, _SYMBOLS.PARENTHESES_OPEN)
		expListE = Element(ELEMENTS.EXPRESSION_LIST)
		nArgs = 0
		while not (self.nextTok.type == tokenizor.SYMBOL and self.nextTok.value == _SYMBOLS.PARENTHESES_CLOSE):
			self._compileExpression(expListE)
			self._readSymbolOptional(expListE, _SYMBOLS.COMMA)
			nArgs += 1
		# hack for TextComparer
		if len(expListE) == 0:
			expListE.text = "\n"
		parent.append(expListE)
		self._readSymbol(parent, _SYMBOLS.PARENTHESES_CLOSE)
		return nArgs

	def _compileDo(self, parent):
		statementE = Element(ELEMENTS.STATEMENT_DO)
		self._readKeyword(statementE, _STATEMENTS.DO)
		identifier = self._readIdentifier(statementE)
		nArgs = 0
		if self._readSymbolOptional(statementE, _SYMBOLS.DOT):
			type_ = self._symbol_table.typeOf(identifier)
			if type_:
				segment, index = self._identifier_data(identifier)
				self.writer.writePush(segment, index)
				nArgs += 1
				identifier = "%s.%s" % (type_, self._readIdentifier(statementE))
			else:
				identifier = "%s.%s" % (identifier, self._readIdentifier(statementE))
		else:
			identifier = "%s.%s" % (self.className, identifier)
			self.writer.writePush(SEGMENT.POINTER, 0)
			nArgs += 1
		nArgs += self._compileExpressionList(statementE)
		self._readSymbol(statementE, _SYMBOLS.SEMI_COLON)
		self.writer.writeCall(identifier, nArgs)
		self.writer.writePop(SEGMENT.TEMP, 0)
		parent.append(statementE)

	def _compileVarDec(self, parent):
		nArgs = 0
		while self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value == _KEYWORDS.VAR:
			varDecE = Element(ELEMENTS.VAR_DEC)
			self._readKeyword(varDecE, _KEYWORDS.VAR)
			self._readType(varDecE)
			self._readIdentifier(varDecE)
			nArgs += 1
			while self._readSymbolOptional(varDecE, _SYMBOLS.COMMA):
				self._readIdentifier(varDecE)
				nArgs += 1
			self._readSymbol(varDecE, _SYMBOLS.SEMI_COLON)
			parent.append(varDecE)
		return nArgs

	def _compileParameters(self, parent):
		paramListE = Element(ELEMENTS.PARAM_LIST)
		while (self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _CLASSVARDEC.VAR_TYPES) or self.nextTok.type == tokenizor.IDENTIFIER:
			self._readType(paramListE)
			self._readIdentifier(paramListE)
			self._readSymbolOptional(paramListE, _SYMBOLS.COMMA)
		if len(paramListE) == 0:
			paramListE.text = "\n"
		parent.append(paramListE)

##############################
########## READ ##############
##############################

	def _readTerm(self, parent):
		termE = Element(ELEMENTS.TERM)
		if self.nextTok.type == tokenizor.INTEGER:
			self.next()
			termE.append(_leafElement(ELEMENTS.INTEGER_CONSTANT, self.tok.value))
			self.writer.writePush(SEGMENT.CONST, self.tok.value)
		elif self.nextTok.type == tokenizor.STRING:
			self.next()
			termE.append(_leafElement(ELEMENTS.STRING_CONSTANT, self.tok.value))
			string_value = self.tok.value
			self.writer.writePush(SEGMENT.CONST, len(string_value))
			self.writer.writeCall("String.new", 1)
			for char in string_value:
				self.writer.writePush(SEGMENT.CONST, ord(char))
				self.writer.writeCall("String.appendChar", 2)
		elif self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _KEYWORDS.CONSTANTS:
			self.next()
			termE.append(_leafElement(ELEMENTS.KEYWORD, self.tok.value))
			_KW_CONT_WRITE[self.tok.value](self.writer)
		elif self.nextTok.type == tokenizor.IDENTIFIER:
			identifier = self._readIdentifier(termE)
			nArgs = 0
			if self._readSymbolOptional(termE, _SYMBOLS.BRACKET_OPEN):
				self._compileExpression(termE)
				self.writer.writePush(*self._identifier_data(identifier))
				self.writer.writeArithmetic("add")
				self.writer.writePop(SEGMENT.POINTER, 1)
				self.writer.writePush(SEGMENT.THAT, 0)
				self._readSymbol(termE, _SYMBOLS.BRACKET_CLOSE)
			elif self.nextTok.type == tokenizor.SYMBOL and self.nextTok.value == _SYMBOLS.PARENTHESES_OPEN:
				nArgs = self._compileExpressionList(termE)
				self._readSymbol(termE, _SYMBOLS.PARENTHESES_CLOSE)
				self.writer.writeCall(identifier, nArgs)
			elif self._readSymbolOptional(termE, _SYMBOLS.DOT):
				type_ = self._symbol_table.typeOf(identifier)
				if type_:
					segment, index = self._identifier_data(identifier)
					self.writer.writePush(segment, index)
					nArgs += 1
					identifier = "%s.%s" % (type_, self._readIdentifier(termE))
				else:
					identifier = "%s.%s" % (identifier, self._readIdentifier(termE))
				nArgs += self._compileExpressionList(termE)
				self.writer.writeCall(identifier, nArgs)
			else:
				self.writer.writePush(*self._identifier_data(identifier))
		elif self.nextTok.type == tokenizor.SYMBOL and self.nextTok.value == _SYMBOLS.PARENTHESES_OPEN:
			self.next()
			termE.append(_leafElement(ELEMENTS.SYMBOL, self.tok.value))
			self._compileExpression(termE)
			self._readSymbol(termE, _SYMBOLS.PARENTHESES_CLOSE)
		elif self.nextTok.type == tokenizor.SYMBOL and self.nextTok.value in _SYMBOLS.UNARY_OPARTORS:
			self.next()
			sym = self.tok.value
			termE.append(_leafElement(ELEMENTS.SYMBOL, self.tok.value))
			self._readTerm(termE)
			self.writer.writeArithmeticUnary(sym)
		else:
			raise self._syntaxError("Unexpected %s." % self.tok.value)
		parent.append(termE)

	def _identifier_data(self, identifier):
		return _SEG_TRANSLATE[self._symbol_table.kindOf(identifier)], self._symbol_table.indexOf(identifier)

	def _readIdentifier(self, parent):
		self.next()
		self._assertToken(self.tok, ELEMENTS.IDENTIFIER, type_=tokenizor.IDENTIFIER)
		name = self.tok.value
		element = _leafElement(ELEMENTS.IDENTIFIER, name)
		type_ = self._symbol_table.typeOf(name)
		kind = None
		index = None
		if type_ is None:
			if parent.tag in (ELEMENTS.CLASSVARDEC, ELEMENTS.VAR_DEC) and len(parent) > 1:
				type_ = parent[1].text
				kind = _SYM_KIND_MAP[parent[0].text]
			elif parent.tag == ELEMENTS.PARAM_LIST and len(parent) > 0:
				type_ = parent[-1].text
				kind = SYM_KINDS.ARG
			if kind is not None:
				index = self._symbol_table.define(name, type_, kind)
		else:
			type_ = self._symbol_table.typeOf(name)
			kind = self._symbol_table.kindOf(name)
			index = self._symbol_table.indexOf(name)
		if kind is not None:
			element.set("type", type_)
			element.set("kind", str(kind))
			element.set("index", str(index))
		parent.append(element)
		return name

	def _readType(self, parent):
		if self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _CLASSVARDEC.VAR_TYPES:
			self.next()
			parent.append(_leafElement(ELEMENTS.KEYWORD, self.tok.value))
		else:
			self._readIdentifier(parent)

	def _readReturnType(self, parent):
		if self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _SUBROUTINEDEC.RETURN_TYPES:
			self.next()
			parent.append(_leafElement(ELEMENTS.KEYWORD, self.tok.value))
		else:
			self._readIdentifier(parent)

	def _readSymbol(self, parent, expected = None):
		self.next()
		expectedStr = expected if expected is not None else ELEMENTS.SYMBOL
		self._assertToken(self.tok, expectedStr, type_=tokenizor.SYMBOL)
		if expected is not None:
			self._assertToken(self.tok, expected, value_=expected)
		parent.append(_leafElement(ELEMENTS.SYMBOL, self.tok.value))
		return self.tok.value

	def _readKeyword(self, parent, expected = None):
		self.next()
		expectedStr = expected if expected is not None else ELEMENTS.KEYWORD
		self._assertToken(self.tok, expectedStr, type_=tokenizor.KEYWORD)
		if expected is not None:
			self._assertToken(self.tok, expected, value_=expected)
		parent.append(_leafElement(ELEMENTS.KEYWORD, self.tok.value))
		return self.tok.value

	def _readSymbolOptional(self, parent, expected):
		if self.nextTok.type == tokenizor.SYMBOL and self.nextTok.value == expected:
			self.next()
			parent.append(_leafElement(ELEMENTS.SYMBOL, self.tok.value))
			return True
		return False

	def _readKeywordOptional(self, parent, expected):
		if self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value == expected:
			self.next()
			parent.append(_leafElement(ELEMENTS.KEYWORD, self.tok.value))
			return True
		return False

	def next(self):
		self.tok = self.iter.next()
		self.nextTok = self.iter.lookahead()

	def _assertToken(self, tok, expected_str, type_ = None, value_ = None):
		if (type_ != None and tok.type != type_) or (value_ != None and tok.value != value_):
			raise self._syntaxError("Expected %s but found %s" % (expected_str, tok.value), tok)

	def _syntaxError(self, msg, tok = None):
		if tok is None:
			tok = self.tok
		return SyntaxError(msg, (None, tok.srow, tok.scol, tok.line))
Exemplo n.º 4
0
class CompilationEngine:
    def __init__(self, source, destination):
        self.src = source
        self.dst = destination
        self.writer = VMWriter(destination)
        self.iter = Lookahead(tokenizor.newTokenizor(self.src))
        self._symbol_table = SymbolTable()

    def compile(self):
        root = self._compileClass()
        return root

    def _compileClass(self):
        classE = Element(ELEMENTS.CLASS)
        self._readKeyword(classE, ELEMENTS.CLASS)
        self.className = self._readIdentifier(classE)
        self._readSymbol(classE, _SYMBOLS.BRACKET_CURLY_OPEN)
        self._compileClassVarDec(classE)
        self._compileSubroutine(classE)
        self._readSymbol(classE, _SYMBOLS.BRACKET_CURLY_CLOSE)
        return classE

    def _compileClassVarDec(self, parent):
        while self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _CLASSVARDEC.FIELD_TYPES:
            classVarDecE = Element(ELEMENTS.CLASSVARDEC)
            self._readKeyword(classVarDecE)
            self._readType(classVarDecE)
            self._readIdentifier(classVarDecE)
            while self._readSymbolOptional(classVarDecE, _SYMBOLS.COMMA):
                self._readIdentifier(classVarDecE)
            self._readSymbol(classVarDecE, _SYMBOLS.SEMI_COLON)
            parent.append(classVarDecE)

    def _compileSubroutine(self, parent):
        while self.nextTok and self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _SUBROUTINEDEC.TYPES:
            subroutineDecE = Element(ELEMENTS.SUBROUTINEDEC)
            function_type = self._readKeyword(subroutineDecE)
            self._readReturnType(subroutineDecE)
            self.methodName = self._readIdentifier(subroutineDecE)
            self._symbol_table.startSubroutine(self.className, self.methodName)
            if function_type == _SUBROUTINEDEC.METHOD:
                self._symbol_table.define("this", self.className,
                                          SYM_KINDS.ARG)
            self._uid = -1
            self._readSymbol(subroutineDecE, _SYMBOLS.PARENTHESES_OPEN)
            self._compileParameters(subroutineDecE)
            self._readSymbol(subroutineDecE, _SYMBOLS.PARENTHESES_CLOSE)
            self._compileSubroutineBody(subroutineDecE, function_type)
            parent.append(subroutineDecE)

    def _gen_label(self, type_):
        self._uid += 1
        return "%s.%s.%s.%d" % (self.className, self.methodName, type_,
                                self._uid)

    def _gen_labels(self, *parts):
        self._uid += 1
        return [
            "%s.%s.%s.%d" % (self.className, self.methodName, part, self._uid)
            for part in parts
        ]

    def _compileSubroutineBody(self, parent, function_type):
        bodyE = Element(ELEMENTS.SUBROUTINEBODY)
        self._readSymbol(bodyE, _SYMBOLS.BRACKET_CURLY_OPEN)
        nArgs = self._compileVarDec(bodyE)
        function_name = parent[2].text
        function_full_name = "%s.%s" % (self.className, function_name)
        self.writer.writeFunction(function_full_name, nArgs)
        if function_type == _SUBROUTINEDEC.CONSTRUCTOR:
            field_count = self._symbol_table.varCount(SYM_KINDS.FIELD)
            self.writer.writePush(SEGMENT.CONST, field_count)
            self.writer.writeCall("Memory.alloc", 1)
            self.writer.writePop(SEGMENT.POINTER, 0)
        elif function_type == _SUBROUTINEDEC.METHOD:
            self.writer.writePush(SEGMENT.ARG, 0)
            self.writer.writePop(SEGMENT.POINTER, 0)
        self._compileStatements(bodyE)
        self._readSymbol(bodyE, _SYMBOLS.BRACKET_CURLY_CLOSE)
        parent.append(bodyE)

    def _compileStatements(self, parent):
        statementsE = Element(ELEMENTS.STATEMENTS)
        while self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _STATEMENTS.TYPE_NAMES:
            if self.nextTok.value == _STATEMENTS.LET:
                statementE = Element(ELEMENTS.STATEMENT_LET)
                self._readKeyword(statementE)
                identifier = self._readIdentifier(statementE)
                is_array = False
                if self._readSymbolOptional(statementE, _SYMBOLS.BRACKET_OPEN):
                    is_array = True
                    self._compileExpression(statementE)
                    self.writer.writePush(*self._identifier_data(identifier))
                    self.writer.writeArithmetic("add")
                    self._readSymbol(statementE, _SYMBOLS.BRACKET_CLOSE)
                self._readSymbol(statementE, _SYMBOLS.EQUAL)
                self._compileExpression(statementE)
                self._readSymbol(statementE, _SYMBOLS.SEMI_COLON)
                if is_array:
                    self.writer.writePop(SEGMENT.TEMP, 0)
                    self.writer.writePop(SEGMENT.POINTER, 1)
                    self.writer.writePush(SEGMENT.TEMP, 0)
                    self.writer.writePop(SEGMENT.THAT, 0)
                else:
                    self.writer.writePop(*self._identifier_data(identifier))
                statementsE.append(statementE)
            elif self.nextTok.value == _STATEMENTS.IF:
                label_else, label_end = self._gen_labels("if.else", "if.end")
                statementE = Element(ELEMENTS.STATEMENT_IF)
                self._readKeyword(statementE)
                self._readSymbol(statementE, _SYMBOLS.PARENTHESES_OPEN)
                self._compileExpression(statementE)
                self._readSymbol(statementE, _SYMBOLS.PARENTHESES_CLOSE)
                self.writer.writeArithmetic("not")
                self.writer.writeIf(label_else)
                self._readSymbol(statementE, _SYMBOLS.BRACKET_CURLY_OPEN)
                self._compileStatements(statementE)
                self._readSymbol(statementE, _SYMBOLS.BRACKET_CURLY_CLOSE)
                self.writer.writeGoto(label_end)
                self.writer.writeLabel(label_else)
                if self._readKeywordOptional(statementE, _KEYWORDS.ELSE):
                    self._readSymbol(statementE, _SYMBOLS.BRACKET_CURLY_OPEN)
                    self._compileStatements(statementE)
                    self._readSymbol(statementE, _SYMBOLS.BRACKET_CURLY_CLOSE)
                self.writer.writeLabel(label_end)
                statementsE.append(statementE)
            elif self.nextTok.value == _STATEMENTS.WHILE:
                label_start, label_end = self._gen_labels(
                    "while.start", "while.end")
                self.writer.writeLabel(label_start)
                statementE = Element(ELEMENTS.STATEMENT_WHILE)
                self._readKeyword(statementE)
                self._readSymbol(statementE, _SYMBOLS.PARENTHESES_OPEN)
                self._compileExpression(statementE)
                self._readSymbol(statementE, _SYMBOLS.PARENTHESES_CLOSE)
                self.writer.writeArithmetic("not")
                self.writer.writeIf(label_end)
                self._readSymbol(statementE, _SYMBOLS.BRACKET_CURLY_OPEN)
                self._compileStatements(statementE)
                self._readSymbol(statementE, _SYMBOLS.BRACKET_CURLY_CLOSE)
                statementsE.append(statementE)
                self.writer.writeGoto(label_start)
                self.writer.writeLabel(label_end)
            elif self.nextTok.value == _STATEMENTS.DO:
                self._compileDo(statementsE)
            elif self.nextTok.value == _STATEMENTS.RETURN:
                statementE = Element(ELEMENTS.STATEMENT_RETURN)
                self._readKeyword(statementE)
                if not (self.nextTok.type == tokenizor.SYMBOL
                        and self.nextTok.value == _SYMBOLS.SEMI_COLON):
                    self._compileExpression(statementE)
                else:
                    self.writer.writePush(SEGMENT.CONST, 0)
                self._readSymbol(statementE, _SYMBOLS.SEMI_COLON)
                self.writer.writeReturn()
                statementsE.append(statementE)
        if len(statementsE) == 0:
            statementsE.text = "\n"
        parent.append(statementsE)

    def _compileExpression(self, parent):
        expressionE = Element(ELEMENTS.EXPRESSION)
        self._readTerm(expressionE)
        while self.nextTok.type == tokenizor.SYMBOL and self.nextTok.value in _SYMBOLS.OPERATORS:
            symbol = self._readSymbol(expressionE)
            self._readTerm(expressionE)
            self.writer.writeArithmetic(symbol)
        parent.append(expressionE)

    def _compileExpressionList(self, parent):
        self._readSymbol(parent, _SYMBOLS.PARENTHESES_OPEN)
        expListE = Element(ELEMENTS.EXPRESSION_LIST)
        nArgs = 0
        while not (self.nextTok.type == tokenizor.SYMBOL
                   and self.nextTok.value == _SYMBOLS.PARENTHESES_CLOSE):
            self._compileExpression(expListE)
            self._readSymbolOptional(expListE, _SYMBOLS.COMMA)
            nArgs += 1
        # hack for TextComparer
        if len(expListE) == 0:
            expListE.text = "\n"
        parent.append(expListE)
        self._readSymbol(parent, _SYMBOLS.PARENTHESES_CLOSE)
        return nArgs

    def _compileDo(self, parent):
        statementE = Element(ELEMENTS.STATEMENT_DO)
        self._readKeyword(statementE, _STATEMENTS.DO)
        identifier = self._readIdentifier(statementE)
        nArgs = 0
        if self._readSymbolOptional(statementE, _SYMBOLS.DOT):
            type_ = self._symbol_table.typeOf(identifier)
            if type_:
                segment, index = self._identifier_data(identifier)
                self.writer.writePush(segment, index)
                nArgs += 1
                identifier = "%s.%s" % (type_,
                                        self._readIdentifier(statementE))
            else:
                identifier = "%s.%s" % (identifier,
                                        self._readIdentifier(statementE))
        else:
            identifier = "%s.%s" % (self.className, identifier)
            self.writer.writePush(SEGMENT.POINTER, 0)
            nArgs += 1
        nArgs += self._compileExpressionList(statementE)
        self._readSymbol(statementE, _SYMBOLS.SEMI_COLON)
        self.writer.writeCall(identifier, nArgs)
        self.writer.writePop(SEGMENT.TEMP, 0)
        parent.append(statementE)

    def _compileVarDec(self, parent):
        nArgs = 0
        while self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value == _KEYWORDS.VAR:
            varDecE = Element(ELEMENTS.VAR_DEC)
            self._readKeyword(varDecE, _KEYWORDS.VAR)
            self._readType(varDecE)
            self._readIdentifier(varDecE)
            nArgs += 1
            while self._readSymbolOptional(varDecE, _SYMBOLS.COMMA):
                self._readIdentifier(varDecE)
                nArgs += 1
            self._readSymbol(varDecE, _SYMBOLS.SEMI_COLON)
            parent.append(varDecE)
        return nArgs

    def _compileParameters(self, parent):
        paramListE = Element(ELEMENTS.PARAM_LIST)
        while (self.nextTok.type == tokenizor.KEYWORD
               and self.nextTok.value in _CLASSVARDEC.VAR_TYPES
               ) or self.nextTok.type == tokenizor.IDENTIFIER:
            self._readType(paramListE)
            self._readIdentifier(paramListE)
            self._readSymbolOptional(paramListE, _SYMBOLS.COMMA)
        if len(paramListE) == 0:
            paramListE.text = "\n"
        parent.append(paramListE)

##############################
########## READ ##############
##############################

    def _readTerm(self, parent):
        termE = Element(ELEMENTS.TERM)
        if self.nextTok.type == tokenizor.INTEGER:
            self.next()
            termE.append(
                _leafElement(ELEMENTS.INTEGER_CONSTANT, self.tok.value))
            self.writer.writePush(SEGMENT.CONST, self.tok.value)
        elif self.nextTok.type == tokenizor.STRING:
            self.next()
            termE.append(_leafElement(ELEMENTS.STRING_CONSTANT,
                                      self.tok.value))
            string_value = self.tok.value
            self.writer.writePush(SEGMENT.CONST, len(string_value))
            self.writer.writeCall("String.new", 1)
            for char in string_value:
                self.writer.writePush(SEGMENT.CONST, ord(char))
                self.writer.writeCall("String.appendChar", 2)
        elif self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _KEYWORDS.CONSTANTS:
            self.next()
            termE.append(_leafElement(ELEMENTS.KEYWORD, self.tok.value))
            _KW_CONT_WRITE[self.tok.value](self.writer)
        elif self.nextTok.type == tokenizor.IDENTIFIER:
            identifier = self._readIdentifier(termE)
            nArgs = 0
            if self._readSymbolOptional(termE, _SYMBOLS.BRACKET_OPEN):
                self._compileExpression(termE)
                self.writer.writePush(*self._identifier_data(identifier))
                self.writer.writeArithmetic("add")
                self.writer.writePop(SEGMENT.POINTER, 1)
                self.writer.writePush(SEGMENT.THAT, 0)
                self._readSymbol(termE, _SYMBOLS.BRACKET_CLOSE)
            elif self.nextTok.type == tokenizor.SYMBOL and self.nextTok.value == _SYMBOLS.PARENTHESES_OPEN:
                nArgs = self._compileExpressionList(termE)
                self._readSymbol(termE, _SYMBOLS.PARENTHESES_CLOSE)
                self.writer.writeCall(identifier, nArgs)
            elif self._readSymbolOptional(termE, _SYMBOLS.DOT):
                type_ = self._symbol_table.typeOf(identifier)
                if type_:
                    segment, index = self._identifier_data(identifier)
                    self.writer.writePush(segment, index)
                    nArgs += 1
                    identifier = "%s.%s" % (type_, self._readIdentifier(termE))
                else:
                    identifier = "%s.%s" % (identifier,
                                            self._readIdentifier(termE))
                nArgs += self._compileExpressionList(termE)
                self.writer.writeCall(identifier, nArgs)
            else:
                self.writer.writePush(*self._identifier_data(identifier))
        elif self.nextTok.type == tokenizor.SYMBOL and self.nextTok.value == _SYMBOLS.PARENTHESES_OPEN:
            self.next()
            termE.append(_leafElement(ELEMENTS.SYMBOL, self.tok.value))
            self._compileExpression(termE)
            self._readSymbol(termE, _SYMBOLS.PARENTHESES_CLOSE)
        elif self.nextTok.type == tokenizor.SYMBOL and self.nextTok.value in _SYMBOLS.UNARY_OPARTORS:
            self.next()
            sym = self.tok.value
            termE.append(_leafElement(ELEMENTS.SYMBOL, self.tok.value))
            self._readTerm(termE)
            self.writer.writeArithmeticUnary(sym)
        else:
            raise self._syntaxError("Unexpected %s." % self.tok.value)
        parent.append(termE)

    def _identifier_data(self, identifier):
        return _SEG_TRANSLATE[self._symbol_table.kindOf(
            identifier)], self._symbol_table.indexOf(identifier)

    def _readIdentifier(self, parent):
        self.next()
        self._assertToken(self.tok,
                          ELEMENTS.IDENTIFIER,
                          type_=tokenizor.IDENTIFIER)
        name = self.tok.value
        element = _leafElement(ELEMENTS.IDENTIFIER, name)
        type_ = self._symbol_table.typeOf(name)
        kind = None
        index = None
        if type_ is None:
            if parent.tag in (ELEMENTS.CLASSVARDEC,
                              ELEMENTS.VAR_DEC) and len(parent) > 1:
                type_ = parent[1].text
                kind = _SYM_KIND_MAP[parent[0].text]
            elif parent.tag == ELEMENTS.PARAM_LIST and len(parent) > 0:
                type_ = parent[-1].text
                kind = SYM_KINDS.ARG
            if kind is not None:
                index = self._symbol_table.define(name, type_, kind)
        else:
            type_ = self._symbol_table.typeOf(name)
            kind = self._symbol_table.kindOf(name)
            index = self._symbol_table.indexOf(name)
        if kind is not None:
            element.set("type", type_)
            element.set("kind", str(kind))
            element.set("index", str(index))
        parent.append(element)
        return name

    def _readType(self, parent):
        if self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _CLASSVARDEC.VAR_TYPES:
            self.next()
            parent.append(_leafElement(ELEMENTS.KEYWORD, self.tok.value))
        else:
            self._readIdentifier(parent)

    def _readReturnType(self, parent):
        if self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value in _SUBROUTINEDEC.RETURN_TYPES:
            self.next()
            parent.append(_leafElement(ELEMENTS.KEYWORD, self.tok.value))
        else:
            self._readIdentifier(parent)

    def _readSymbol(self, parent, expected=None):
        self.next()
        expectedStr = expected if expected is not None else ELEMENTS.SYMBOL
        self._assertToken(self.tok, expectedStr, type_=tokenizor.SYMBOL)
        if expected is not None:
            self._assertToken(self.tok, expected, value_=expected)
        parent.append(_leafElement(ELEMENTS.SYMBOL, self.tok.value))
        return self.tok.value

    def _readKeyword(self, parent, expected=None):
        self.next()
        expectedStr = expected if expected is not None else ELEMENTS.KEYWORD
        self._assertToken(self.tok, expectedStr, type_=tokenizor.KEYWORD)
        if expected is not None:
            self._assertToken(self.tok, expected, value_=expected)
        parent.append(_leafElement(ELEMENTS.KEYWORD, self.tok.value))
        return self.tok.value

    def _readSymbolOptional(self, parent, expected):
        if self.nextTok.type == tokenizor.SYMBOL and self.nextTok.value == expected:
            self.next()
            parent.append(_leafElement(ELEMENTS.SYMBOL, self.tok.value))
            return True
        return False

    def _readKeywordOptional(self, parent, expected):
        if self.nextTok.type == tokenizor.KEYWORD and self.nextTok.value == expected:
            self.next()
            parent.append(_leafElement(ELEMENTS.KEYWORD, self.tok.value))
            return True
        return False

    def next(self):
        self.tok = self.iter.next()
        self.nextTok = self.iter.lookahead()

    def _assertToken(self, tok, expected_str, type_=None, value_=None):
        if (type_ != None and tok.type != type_) or (value_ != None
                                                     and tok.value != value_):
            raise self._syntaxError(
                "Expected %s but found %s" % (expected_str, tok.value), tok)

    def _syntaxError(self, msg, tok=None):
        if tok is None:
            tok = self.tok
        return SyntaxError(msg, (None, tok.srow, tok.scol, tok.line))