def Goal(self):
if self.lex.token in ['num', 'var', '(']:
val = self.Expr()
self.lex.match('\0') # expression?
print(val)
elif self.lex.token == 'set': # set command?
self.Assign()
self.lex.match('\0')
else:
raise SyntaxError()
def Goal(self):
if self.lex.token in ['num', 'var', '(']:
tree = self.Expr()
self.lex.match('\0')
return tree
elif self.lex.token == 'set':
tree = self.Assign()
self.lex.match('\0')
return tree
else:
raise SyntaxError()
def Factor(self):
left = self.Term()
while True:
if self.lex.token in ['+', '-', '\0', ')']:
return left
elif self.lex.token == '*':
self.lex.scan()
left = TimesNode(left, self.Term())
elif self.lex.token == '/':
self.lex.scan()
left = DivideNode(left, self.Term())
else:
raise SyntaxError()
def Expr(self):
left = self.Factor() # left subtree
while True:
if self.lex.token in ['\0', ')']:
return left
elif self.lex.token == '+':
self.lex.scan()
left = PlusNode(left, self.Factor()) # add root-node
elif self.lex.token == '-':
self.lex.scan()
left = MinusNode(left, self.Factor()) # grows up/right
else:
raise SyntaxError()
def Factor(self):
left = self.Term()
while True:
if self.lex.token in ['+', '-', '\0', ')']:
return left
elif self.lex.token == '*':
self.lex.scan()
left = left * self.Term()
elif self.lex.token == '/':
self.lex.scan()
left = left / self.Term()
else:
raise SyntaxError()
def Expr(self):
left = self.Factor()
while True:
if self.lex.token in ['\0', ')']:
return left
elif self.lex.token == '+':
self.lex.scan()
left = left + self.Factor()
elif self.lex.token == '-':
self.lex.scan()
left = left - self.Factor()
else:
raise SyntaxError()
def Expr(self): # 构造表达式?
left = self.Factor()
while True:
if self.lex.token in ['\0', ')']: # '\0'句子结束符或者式子中的')'
return left
elif self.lex.token == '+': # 最后处理'+', '-'
self.lex.scan()
left = left + self.Factor()
elif self.lex.token == '-':
self.lex.scan()
left = left - self.Factor()
else:
raise SyntaxError()
def Term(self):
if self.lex.token == 'num':
leaf = NumNode(self.lex.match('num'))
return leaf
elif self.lex.token == 'var':
leaf = VarNode(self.lex.value, self.lex.start)
self.lex.scan()
return leaf
elif self.lex.token == '(':
self.lex.scan()
tree = self.Expr()
self.lex.match(')')
return tree
else:
raise SyntaxError()
def Term(self):
if self.lex.token == 'num':
val = self.lex.match('num') # numbers
return val
elif self.lex.token == 'var':
if self.lex.value in self.vars.keys(): # keys(): EIBTI!
val = self.vars[self.lex.value] # look up name's value
self.lex.scan()
return val
else:
raise UndefinedError(self.lex.value)
elif self.lex.token == '(':
self.lex.scan()
val = self.Expr() # sub-expression
self.lex.match(')')
return val
else:
raise SyntaxError()