rpn.py

import operator

from purplex import Lexer, Parser, TokenDef, attach


class RPNLexer(Lexer):

    INTEGER = TokenDef(r'\d+')

    MULTIPLY = TokenDef(r'\*')
    DIVIDE = TokenDef(r'/')
    PLUS = TokenDef(r'\+')
    MINUS = TokenDef(r'-')

    WHITESPACE = TokenDef(r'[\s\n]+', ignore=True)

    def on_token(self, token):
        if token.value.strip():
            print('parsed token:', token.value)


class RPNParser(Parser):

    LEXER = RPNLexer
    START = 'e'

    PRECEDENCE = (
        ('left', 'INTEGER'),
    )

    OPERATORS = {
        '*': operator.mul,
        '/': operator.ifloordiv,
        '+': operator.add,
        '-': operator.sub,
    }

    @attach('e : e e MULTIPLY')
    @attach('e : e e DIVIDE')
    @attach('e : e e PLUS')
    @attach('e : e e MINUS')
    def binop(self, *args):
        return self.OPERATORS[args[2]](args[0], args[1])

    @attach('e : INTEGER')
    def integer(self, number):
        return int(number)


if __name__ == '__main__':
    line = input('>> ')
    print('input is', line)
    print(RPNParser().parse(line))