parserlib

A Pythonic parser implementation!

Installation

    pip install parserlib

Example

from parserlib.lexer import Lexer
from parserlib.parser import Rule, ShiftReduceParser
from parserlib.token import Token


class NumberToken(Token):
    name = "NUMBER"
    regex = r"\d+"


class PlusToken(Token):
    name = "PLUS"
    regex = r"\+"


class MinusToken(Token):
    name = "MINUS"
    regex = r"-"


class LeftParenthesisToken(Token):
    name = "LEFT_PARENTHESIS"
    regex = r"\("


class RightParenthesisToken(Token):
    name = "RIGHT_PARENTHESIS"
    regex = r"\)"


class AsteriskToken(Token):
    name = "ASTERISK"
    regex = r"\*"


class SlashToken(Token):
    name = "SLASH"
    regex = r"/"


class Expression(Rule):
    pass


class NumberExpression(Expression):
    def __init__(self, number: NumberToken):
        self.number = number

    @classmethod
    def reduce(cls, number: NumberToken) -> Expression:
        return cls(number)


class ParenthesisExpression(Expression):
    @classmethod
    def reduce(
        cls, _: LeftParenthesisToken, expression: Expression, __: RightParenthesisToken
    ) -> Expression:
        return expression


class PlusExpression(Expression):
    def __init__(self, left: Expression, right: Expression):
        self.left = left
        self.right = right

    @classmethod
    def reduce(cls, left: Expression, _: PlusToken, right: Expression) -> Expression:
        return cls(left, right)


class MinusExpression(Expression):
    def __init__(self, left: Expression, right: Expression):
        self.left = left
        self.right = right

    @classmethod
    def reduce(cls, left: Expression, _: MinusToken, right: Expression) -> Expression:
        return cls(left, right)


class TimesExpression(Expression):
    def __init__(self, left: Expression, right: Expression):
        self.left = left
        self.right = right

    @classmethod
    def reduce(
        cls, left: Expression, _: AsteriskToken, right: Expression
    ) -> Expression:
        return cls(left, right)


class DivideExpression(Expression):
    def __init__(self, left: Expression, right: Expression):
        self.left = left
        self.right = right

    @classmethod
    def reduce(cls, left: Expression, _: SlashToken, right: Expression) -> Expression:
        return cls(left, right)


lexer = Lexer(
    tokens=(
        NumberToken,
        PlusToken,
        MinusToken,
        LeftParenthesisToken,
        RightParenthesisToken,
        AsteriskToken,
        SlashToken,
    ),
    ignore_characters=" \t",
)
parser = ShiftReduceParser(
    rules=(
        ParenthesisExpression,
        PlusExpression,
        MinusExpression,
        TimesExpression,
        DivideExpression,
        NumberExpression,
    ),
    precedence=(
        (ParenthesisExpression,),
        (TimesExpression, DivideExpression),
        (PlusExpression, MinusExpression),
    ),
)
tree = parser.parse(lexer.feed("1 + \n(2) * 3"))
print(tree)