def __init__(self, filename):
self.lex = Lexical_Analyzers(filename)
class Parsers(object):
def __init__(self, filename):
self.lex = Lexical_Analyzers(filename)
def parse(self):
self.match('main')
self.match ('(')
self.match (')')
statementList = self.getStatementList()
return Programs(statementList)
def match(self, expected):
token = self.lex.getToken()
if token != expected:
raise ParserExceptions ("Match Error")
def getStatementList(self):
statementList = StatementLists()
statement = self.getStatement()
statementList.add(statement)
token = self.lex.lookAhead()
while token == ";" :
self.match(";")
statement = self.getStatement()
statementList.add(statement)
token = self.lex.lookAhead()
return statementList
def getStatement(self):
token = self.lex.lookAhead()
if token == "if":
stmt = self.getIfStatement()
elif token == "while":
stmt = self.getWhileStatement()
elif token == "display":
stmt = self.getDisplayStatement()
else:
stmt = self.getAssignmentStatement()
return stmt
def getIfStatement(self):
self.match ('if')
expr = self.getBooleanExpression()
self.match('then')
stmt1 = self.getStatementList()
self.match('else')
stmt2 = self.getStatementList()
self.match('end')
return ifStatements(expr, stmt1, stmt2)
def getWhileStatement(self):
self.match('while')
expr = self.getBooleanExpression()
self.match('do')
stmt = self.getStatementList()
self.match('end')
return WhileStatements(expr,stmt)
def getId(self):
token = self.lex.getToken()
if len(token)!= 1:
raise ParserExceptions ("id expected")
return IdS (token)
def getDisplayStatement(self):
self.match('display')
self.match('(')
var = self.getId()
self.match(')')
return DisplayStatements(var)
def getAssignmentStatement(self):
var = self.getId()
self.match('<-')
expr = self.getArithmeticExpression()
return AssignmentStatements(var, expr)
def getArithmeticExpression (self):
token = self.lex.lookAhead()
if self.isValidArithmeticOp(token):
op = self.getArithmeticOperator()
op1 = self.getOperand()
op2 = self.getOperand()
expr = self.createArithmeticExpression(op, op1, op2)
else:
op3 = self.getOperand()
expr = UnaryExpressions(op3)
return expr
def isValidArithmeticOp(self, token):
return token == '+' or token =='-' or token == '*' or token == '/'
def createArithmeticExpression(self,op, op1, op2):
if op == 'AddExpressions':
expr = AddExpressions(op1, op2)
elif op == 'SubExpressions':
expr = SubExpressions(op1,op2)
elif op == 'MulExpressions':
expr = MulExpressions(op1,op2)
elif op == 'DivExpressions':
expr = DivExpressions(op1, op2)
else:
raise ParserExceptions ("operator expected")
return expr
def getArithmeticOperator(self):
token = self.lex.getToken()
if token == "+":
op = 'AddExpressions'
elif token == "-":
op = 'SubExpressions'
elif token == "*":
op = 'MulExpressions'
elif token == "/":
op = 'DivExpressions'
else:
raise ParserExceptions ("operator expected")
return op
def getBooleanExpression (self):
op = self.getRelativeOp()
op1 = self.getOperand()
op2 = self.getOperand()
return self.createBooleanExpression(op, op1, op2)
def getRelativeOp(self):
token = self.lex.getToken()
if token == "<":
op = 'LTExpressions'
elif token == "<=":
op = 'LEExpressions'
elif token == ">":
op = 'GTExpressions'
elif token == ">=":
op = 'GEExpressions'
elif token == "=":
op = 'EQExpressions'
elif token == "/=":
op = 'NEExpressions'
return op
def createBooleanExpression(self, op, op1, op2):
if op == 'LTExpressions':
expr = LTExpressions(op1, op2)
elif op == 'LEExpressions':
expr = LEExpressions(op1, op2)
elif op == 'GTExpressions':
expr = GTExpressions(op1, op2)
elif op == 'GEExpressions':
expr = GEExpressions(op1, op2)
elif op == 'EQExpressions':
expr = EQExpressions(op1, op2)
elif op == 'NEExpressions':
expr = NEExpressions(op1, op2)
else:
raise ParserExceptions ("relative operator expected")
return expr
def getOperand(self):
token = self.lex.lookAhead()
if token.isdigit():
op = self.getLiteralInteger()
elif len(token)== 0:
# needs to be exactly 1
raise ParserExceptions ("operand Expected")
else:
op = self.getId()
return op
def getLiteralInteger(self):
token = self.lex.getToken()
return LiteralIntegers(token)