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Parser.py
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Parser.py
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__author__ = 'Chris'
from Lexical_Analyzer import Lexical_Analyzer
from Lexical_Exception import LexicalException
from Parser_Exception import ParserException
from Statement_Block import Statement_Block
from If_Statement import If_Statement
from Statement_List import Statement_List
from Statement import Statement
from Print_Statement import Print_Statement
from While_Statement import While_Statement
from Token import Token
from TokenTypes import TokenType
from Arithmetic_Operator import Arithmetic_Operator
from Relational_Operator import Relational_Operator
from Constant import Constant
from Id import Id
from Binary_Expression import Binary_Expression
from Boolean_Expression import Boolean_Expression
from Program import Program
from Assignment_Statement import Assignment_Statement
class Parser(object):
def __init__(self, fileName):
self.lex = Lexical_Analyzer.__new__(fileName)
def parse(self):
tok = self.get_next_token()
self.match(tok, TokenType.MAIN_TOK)
tok = self.get_next_token()
self.match(tok, TokenType.LEFT_PAREN_TOK)
tok = self.get_next_token()
self.match(tok, TokenType.RIGHT_PAREN_TOK)
tok = self.get_next_token()
self.match(tok, TokenType.EOLN_TOK)
block = self.get_statement_block()
tok = self.get_next_token()
if tok.Token.get_token_type() != TokenType.EOS_TOK:
raise ParserException("invalid end of file")
return Program(block)
def get_statement_block(self):
tok = self.get_next_token()
self.match(tok, TokenType.INDENT_TOK)
stmts = self.get_statement_list()
tok = self.get_next_token()
self.match(tok, TokenType.DEDENT_TOK)
return Statement_Block.__new__(stmts)
def get_statement_list(self):
stmts = Statement_List()
s = self.get_statement()
stmts.add(s)
tok = self.get_look_ahead_token()
while self.is_valid_start_of_statement(tok):
s = self.get_statement()
stmts.add(s)
tok = self.get_look_ahead_token()
return stmts
def is_valid_start_of_statement(self, tok):
if tok.Token.get_token_type() == TokenType.PRINT_TOK or tok.Token.get_token_type() == TokenType.ID_TOK or tok.Token.get_token_type() == TokenType.WHILE_TOK or tok.Token.get_token_type() == TokenType.IF_TOK:
return True
else:
return False
def get_statement(self):
s = Statement()
tok = self.get_look_ahead_token()
if tok.Token.get_token_type() == TokenType.PRINT_TOK:
s = self.get_print_statement()
elif tok.Token.get_token_type() == TokenType.IF_TOK:
s = self.get_if_statement()
elif tok.Token.get_token_type() == TokenType.WHILE_TOK:
s = self.get_while_statement()
else:
s = self.get_assignment_statement()
return s
def get_assignment_statement(self):
var = self.get_id()
tok = self.get_next_token()
self.match(tok, TokenType.ASSIGN_TOK)
expr = self.get_arithmetic_expression()
tok = self.get_next_token()
self.match(tok, TokenType.EOLN_TOK)
return Assignment_Statement.__new__(var, expr)
def get_while_statement(self):
tok = self.get_next_token()
self.match(tok, TokenType.WHILE_TOK)
expr = self.get_boolean_expression()
tok = self.get_next_token()
self.match(tok, TokenType.COLON_TOK)
tok = self.get_next_token()
self.match(tok, TokenType.EOLN_TOK)
block = self.get_statement_block()
return While_Statement.__new__(expr, block)
def get_if_statement(self):
s = If_Statement()
tok = self.get_next_token()
self.match(tok, TokenType.IF_TOK)
expr = self.get_boolean_expression()
s.add_expression(expr)
tok = self.get_next_token()
self.match(tok, TokenType.COLON_TOK)
tok = self.get_next_token()
self.match(tok, TokenType.EOLN_TOK)
block = self.get_statement_block()
s.add_block(block)
tok = self.get_next_token()
while tok.Token.get_token_type() == TokenType.ELIF_TOK:
self.match(tok, TokenType.ELIF_TOK)
expr = self.get_boolean_expression()
s.add_expression(expr)
tok = self.get_next_token()
self.match(tok, TokenType.COLON_TOK)
tok = self.get_next_token()
self.match(tok, TokenType.EOLN_TOK)
block = self.get_statement_block()
s.add_block(block)
tok = self.get_next_token()
self.match(tok, TokenType.ELSE_TOK)
tok = self.get_next_token()
self.match(tok, TokenType.COLON_TOK)
tok = self.get_next_token()
self.match(tok, TokenType.EOLN_TOK)
block = self.get_statement_block()
s.add_block(block)
return s
def get_print_statement(self):
tok = self.get_next_token()
self.match(tok, TokenType.PRINT_TOK)
tok = self.get_next_token()
self.match(tok, TokenType.LEFT_PAREN_TOK)
expr = self.get_arithmetic_expression()
tok = self.get_next_token()
self.match(tok, TokenType.RIGHT_PAREN_TOK)
tok = self.get_next_token()
self.match(tok, TokenType.EOLN_TOK)
return Print_Statement.__new__(expr)
def get_boolean_expression(self):
op = self.get_relational_operator()
expr1 = self.get_arithmetic_expression()
expr2 = self.get_arithmetic_expression()
return Boolean_Expression.__new__(op, expr1, expr2)
def get_arithmetic_expression(self):
tok = self.get_look_ahead_token()
if tok.Token.get_token_type() == TokenType.ID_TOK:
expr = self.get_id()
elif tok.Token.get_token_type() == TokenType.CONST_TOK:
expr = self.get_literal_constant()
else:
op = self.get_arithmetic_operator()
expr1 = self.get_arithmetic_expression()
expr2 = self.get_arithmetic_expression()
expr = Binary_Expression.__new__(op, expr1, expr2)
return expr
def get_literal_constant(self):
tok = self.get_next_token()
self.match(tok, TokenType.CONST_TOK)
value = tok.Token.get_lexeme()
return Constant.__new__(value)
def get_relational_operator(self):
tok = self.get_next_token()
if tok.Token.get_token_type() == TokenType.EQ_TOK:
op = Relational_Operator.EQ_OP
if tok.Token.get_token_type() == TokenType.NE_TOK:
op = Relational_Operator.NE_OP
if tok.Token.get_token_type() == TokenType.LE_TOK:
op = Relational_Operator.LE_OP
if tok.Token.get_token_type() == TokenType.LT_TOK:
op = Relational_Operator.LT_OP
if tok.Token.get_token_type() == TokenType.GT_TOK:
op = Relational_Operator.GT_OP
if tok.Token.get_token_type() == TokenType.GE_TOK:
op = Relational_Operator.GE_OP
else:
raise ParserException("relational operator expected")
return op
def get_arithmetic_operator(self):
tok = self.get_next_token()
if tok.Token.get_token_type() == TokenType.ADD_TOK:
op = Arithmetic_Operator.ADD_OP
if tok.Token.get_token_type() == TokenType.SUB_TOK:
op = Arithmetic_Operator.SUB_OP
if tok.Token.get_token_type() == TokenType.MUL_TOK:
op = Arithmetic_Operator.MUL_OP
if tok.Token.get_token_type() == TokenType.DIV_TOK:
op = Arithmetic_Operator.DIV_OP
else:
raise ParserException("arithmetic operator expected")
return op
def get_id(self):
tok = self.get_next_token()
self.match(tok, TokenType.ID_TOK)
return Id.__new__(tok.Token.get_lexeme()[0])
def match(self, tok, tokType):
if tok.Token.get_token_type() != tokType:
raise ParserException(str(tokType) + "expected at row " + str(tok.Token.get_row_number()) + " and column "
+ str(tok.Token.get_column_number()))
def get_look_ahead_token(self):
try:
tok = self.lex.get_look_ahead_token()
except LexicalException:
raise ParserException("no more tokens")
return tok
def get_next_token(self):
try:
tok = self.lex.get_next_token()
except LexicalException:
raise ParserException("no more tokens")
return tok