Add 2 functions to solution 5 of order
87568. The program to solution 5 and the new function prompts are attached.
INTEGER, PLUS, MINUS, MUL, DIV, LPAREN, RPAREN, EOF = ( 'INTEGER', 'PLUS', 'MINUS', 'MUL', 'DIV', '(', ')', 'EOF' ) class Token(object): def __init__(self, type, value): self.type = type self.value = value def __str__(self): """String representation of the class instance. Examples: Token(INTEGER, 3) Token(PLUS, '+') Token(MUL, '*') """ return 'Token({type}, {value})'.format( type=self.type, value=repr(self.value) ) def __repr__(self): return self.__str__() class Lexer(object): def __init__(self, text): # client string input, e.g. "4 + 2 * 3 - 6 / 2" self.text = text # self.pos is an index into self.text self.pos = 0 self.current_char = self.text[self.pos] def error(self): raise Exception('Invalid character') def advance(self): """Advance the `pos` pointer and set the `current_char` variable.""" self.pos += 1 if self.pos > len(self.text) - 1: self.current_char = None # Indicates end of input else: self.current_char = self.text[self.pos] def skip_whitespace(self): while self.current_char is not None and self.current_char.isspace(): self.advance() def integer(self): """Return a (multidigit) integer consumed from the input.""" result = '' while self.current_char is not None and self.current_char.isdigit(): result += self.current_char self.advance() return int(result) def get_next_token(self): """Lexical analyzer (also known as scanner or tokenizer) This method is responsible for breaking a sentence apart into tokens. One token at a time. """ while self.current_char is not None: if self.current_char.isspace(): self.skip_whitespace() continue if self.current_char.isdigit(): return Token(INTEGER, self.integer()) if self.current_char == '+': self.advance() return Token(PLUS, '+') if self.current_char == '-': self.advance() return Token(MINUS, '-') if self.current_char == '*': self.advance() return Token(MUL, '*') if self.current_char == '/': self.advance() return Token(DIV, '/') if self.current_char == '(': self.advance() return Token(LPAREN, '(') if self.current_char == ')': self.advance() return Token(RPAREN, ')') self.error() return Token(EOF, None) ############################################################################### # # # PARSER # # # ############################################################################### class AST(object): pass class BinOp(AST): def __init__(self, left, op, right): self.left = left self.token = self.op = op self.right = right class Num(AST): def __init__(self, token): self.token = token self.value = token.value class Parser(object): def __init__(self, lexer): self.lexer = lexer # set current token to the first token taken from the input self.current_token = self.lexer.get_next_token() def error(self): raise Exception('Invalid syntax') def eat(self, token_type): # compare the current token type with the passed token # type and if they match then "eat" the current token # and assign the next token to the self.current_token, # otherwise raise an exception. if self.current_token.type == token_type: self.current_token = self.lexer.get_next_token() else: self.error() def factor(self): """factor : INTEGER | LPAREN expr RPAREN""" token = self.current_token if token.type == INTEGER: self.eat(INTEGER) return Num(token) elif token.type == LPAREN: self.eat(LPAREN) node = self.expr() self.eat(RPAREN) return node def term(self): """term : factor ((MUL | DIV) factor)*""" node = self.factor() while self.current_token.type in (MUL, DIV): token = self.current_token if token.type == MUL: self.eat(MUL) elif token.type == DIV: self.eat(DIV) node = BinOp(left=node, op=token, right=self.factor()) return node def expr(self): """ expr : term ((PLUS | MINUS) term)* term : factor ((MUL | DIV) factor)* factor : INTEGER | LPAREN expr RPAREN """