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Assignment statement grammar (version 1)

The main script for grammar AssignmentStatement1 (version 1)

author

Morteza Zakeri, https://m-zakeri.github.io

date

20201029

Required

  • Compiler generator: ANTLR 4.x
  • Target language(s): Python 3.8.x

Changelog

v2.0.0

  • A lexer and parser for simple grammar without any attribute or listener

Refs

  • Reference: Compiler book by Dr. Saeed Parsa (http://parsa.iust.ac.ir/)
  • Course website: http://parsa.iust.ac.ir/courses/compilers/
  • Laboratory website: http://reverse.iust.ac.ir/

MyListener

Bases: AssignmentStatement1Listener

A simple listener class

Source code in language_apps/assignment_statement_v1/assignment_statement1main.py 
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class MyListener(AssignmentStatement1Listener):
    """
    A simple listener class
    """

    def __init__(self):
        self._count = 0

    def helper(self):
        pass

    def get_count(self):
        return self._count

    def exitFactor(self, ctx: AssignmentStatement1Parser.FactorContext):
        # print('Dummy listener!')
        # self._count += 1
        pass

    def enterExpr(self, ctx: AssignmentStatement1Parser.ExprContext):
        if ctx.getChildCount() == 3:
            if ctx.getChild(1).getText() == '+':
                self._count += 1

    def enterTerm(self, ctx: AssignmentStatement1Parser.TermContext):
        pass

    def exitNumber(self, ctx: AssignmentStatement1Parser.NumberContext):
        pass

main(args)

The main driver to create and use the lexer and parser

Args:

args (namespace):

return (None):

Source code in language_apps/assignment_statement_v1/assignment_statement1main.py 
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def main(args):
    """
    The main driver to create and use the lexer and parser

    Args:

        args (namespace):

    return (None):

    """
    # Step 1: Load input source into stream
    stream = FileStream(args.file, encoding='utf8')
    # input_stream = StdinStream()
    # Step 2: Create an instance of AssignmentStLexer
    lexer = AssignmentStatement1Lexer(stream)
    # Step 3: Convert the input source into a list of tokens
    token_stream = CommonTokenStream(lexer)
    #
    # quit()

    # Step 4: Create an instance of the AssignmentStParser
    parser = AssignmentStatement1Parser(token_stream)
    # parser._interp.predictionMode = PredictionMode.SLL

    # x = DescriptiveErrorListener()
    # parser.addErrorListener()

    # Step 5: Create parse tree
    parse_tree = parser.start()

    print(parse_tree.toStringTree())
    # quit()

    # Step 6: Create an instance of AssignmentStListener
    my_listener = MyListener()
    walker = ParseTreeWalker()
    walker.walk(t=parse_tree, listener=my_listener)

    print(f'Number of "+" operators: {my_listener.get_count()}')

    # print(parse_tree.getText())
    # quit()

    # return
    lexer.reset()
    token = lexer.nextToken()
    while token.type != Token.EOF:
        print('Token text: ', token.text, 'Token line: ', token.line)
        token = lexer.nextToken()