#!/usr/bin/env python3
"""calc — evaluate an arithmetic expression from the command line."""
import sys

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


def main():
    if len(sys.argv) != 2:
        print("usage: calc.py <expression>", file=sys.stderr)
        sys.exit(1)
    try:
        result = evaluate(parse(tokenize(sys.argv[1])))
        print(result)
    except (LexError, ParseError, EvalError) as exc:
        print(f"error: {exc}", file=sys.stderr)
        sys.exit(1)


if __name__ == "__main__":
    main()