reparsec 0.4.0

Parser

reparsec

Small parsec-like parser combinators library with semi-automatic error recovery.

Installation

pip install reparsec

Usage

• Tutorial
• Documentation

Simple arithmetic expression parser and calculator:

from typing import Callable

from reparsec import Delay
from reparsec.scannerless import literal, regexp
from reparsec.sequence import eof


def op_action(op: str) -> Callable[[int, int], int]:
    return {
        "+": lambda a, b: a + b,
        "-": lambda a, b: a - b,
        "*": lambda a, b: a * b,
    }[op]


spaces = regexp(r"\s*")
number = regexp(r"\d+").fmap(int) << spaces
mul_op = regexp(r"[*]").fmap(op_action) << spaces
add_op = regexp(r"[-+]").fmap(op_action) << spaces
l_paren = literal("(") << spaces
r_paren = literal(")") << spaces

expr = Delay[str, int]()
value = number | expr.between(l_paren, r_paren)
expr.define(value.chainl1(mul_op).chainl1(add_op))

parser = expr << eof()

print(parser.parse("1 + 2 * (3 + 4)").unwrap())

Output:

15

Out-of-the-box error recovery:

result = parser.parse("1 + 2 * * (3 + 4)", recover=True)

try:
    result.unwrap()
except ParseError as e:
    print(e)

print(result.unwrap(recover=True))

Output:

at 8: expected '(' (skipped 2 tokens)
15

More examples:

• JSON parser
• Scannerless JSON parser