self.lex.newtext(text[0]) # reuse this parser?
try:
self.lex.scan() # get first token
self.Goal() # parse a sentence
except SyntaxError:
print('Syntax Error at column:', self.lex.start)
self.lex.showerror()
except LexicalError:
print('Lexical Error at column:', self.lex.start)
self.lex.showerror()
except UndefinedError as E:
name = E.args[0]
print("'%s' is undefined at column:" % name, self.lex.start)
self.lex.showerror()
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 Assign(self):
self.lex.match('set')
var = self.lex.match('var')
val = self.Expr()
self.vars[var] = val # assign name in dict
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 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 == '/':
1444 | Chapter 19: Text and Language