#!/usr/bin/env python3
"""calc CLI — evaluate an arithmetic expression given as a single argument."""

import sys


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

    expr = sys.argv[1]
    try:
        from calc.lexer import tokenize, LexError
        from calc.parser import parse, ParseError
        from calc.evaluator import evaluate, EvalError

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


if __name__ == "__main__":
    main()