Function input 

pub fn input<T, E>(
    message: &str,
    default: Option<T>,
    help: Option<&str>,
) -> Result<Option<T>, InputError<E>>
where
    T: Display + FromStr<Err = E> + Clone,
    E: Error + Send + Sync + 'static,

Prompts the user for input. If the user cancels the operation, the operation is interrupted, or no suitable terminal is found, then Ok(None) is returned.