#!/usr/bin/env python3
"""calc.py — command-line calculator: python calc.py "<expression>" """

import sys
from calc.lexer import tokenize, LexError
from calc.parser import parse, ParseError
from calc.evaluator import evaluate, EvalError


def main():
    if len(sys.argv) != 2:
        print("usage: python calc.py \"<expression>\"", file=sys.stderr)
        sys.exit(1)

    expr = sys.argv[1]
    try:
        result = evaluate(parse(tokenize(expr)))
    except (LexError, ParseError, EvalError) as exc:
        print(f"error: {exc}", file=sys.stderr)
        sys.exit(1)

    print(result)


if __name__ == "__main__":
    main()