Brtdku

For the practice, I decided to work on a simple language. When only a single line, my say(); command works fine, but when I do two says in a row, I get an error.

For Parsing I'm using rply. I was following this (https://blog.usejournal.com/writing-your-own-programming-language-and-compiler-with-python-a468970ae6df) guide. I've searched extesively but I cant find a solution.

This is the python code:

from rply import ParserGenerator

from ast import Int, Sum, Sub, Say, String





class Parser():

   def __init__(self):

        self.pg = ParserGenerator(

            # A list of all token names accepted by the parser.

            ['INTEGER', 'SAY', 'OPEN_PAREN', 'CLOSE_PAREN',

             'SEMI_COLON', 'SUM', 'SUB', 'STRING']

        )



    def parse(self):

        @self.pg.production('say : SAY OPEN_PAREN expression CLOSE_PAREN SEMI_COLON')

        def say(p):

            return Say(p[2])



        @self.pg.production('expression : expression SUM expression')

        @self.pg.production('expression : expression SUB expression')

        def expression(p):

            left = p[0]

            right = p[2]

            operator = p[1]

            if operator.gettokentype() == 'SUM':

                return Sum(left, right)

            elif operator.gettokentype() == 'SUB':

                return Sub(left, right)



        @self.pg.production('expression : INTEGER')

        def int(p):

            return Int(p[0].value)



        @self.pg.production('expression : STRING')

        def string(p):

            return String(p[0].value)



        @self.pg.error

        def error_handler(token):

            raise ValueError("Ran into a %s where it wasn't expected" % token.gettokentype())



    def get_parser(self):

        return self.pg.build()

When I run my program with the input of:

say("yo");

It works fine and return yo.
However, when I input:

say("yo");

say("yoyo");

I expect it to return yo yoyo, but instead I get this error:

C:Usersgdog1Desktopprojintparser.py:42: ParserGeneratorWarning: 4 

shift/reduce conflicts

  return self.pg.build()

Traceback (most recent call last):

  File "<input>", line 1, in <module>

  File "C:Program FilesJetBrainsPyCharm Community Edition 2018.3.3helperspydev_pydev_bundlepydev_umd.py", line 197, in runfile

    pydev_imports.execfile(filename, global_vars, local_vars)  # execute the script

  File "C:/Users/gdog1/Desktop/proj/main.py", line 20, in <module>

    parser.parse(tokens).eval()

  File "C:Python27libsite-packagesrplyparser.py", line 60, in parse

    self.error_handler(lookahead)

  File "C:Usersgdog1Desktopprojintparser.py", line 39, in error_handler

    raise ValueError("Ran into a %s where it wasn't expected" % 

token.gettokentype())

ValueError: Ran into a SAY where it wasn't expected  

Your grammar describes a single command:

say : SAY OPEN_PAREN expression CLOSE_PAREN SEMI_COLON

So that is what the parser accepts.

If you want the input to consist of multiple commands, you need to write a grammar which describes that input:

program : 

program : program say

As the error, says its with the below line:

raise ValueError("Ran into a %s where it wasn't expected" % token.gettokentype())

Change it as below and check:

raise ValueError('Ran into a %s where it wasn't expected' % (token.gettokentype()))