fn main() {
    fn count(text: &str) -> Result<u32, &'static str> {
        let value = text.parse::<u32>().map_err(|_| "invalid integer")?;
        if value > 100 { return Err("count too large"); }
        Ok(value)
    }
    assert_eq!(count("8"), Ok(8));
    assert_eq!(count("bad"), Err("invalid integer"));
    assert_eq!(count("101"), Err("count too large"));
    println!("Valid count accepted; format and range errors distinguished");
}