Solution to Bob

bob.rs

enum Sentence {
  Question,
  Yelling,
  Silence,
  Generic
}

pub fn reply(message: &str) -> &str {
  match sentence_type(message) {
    Question => "Sure.",
    Yelling => "Whoa, chill out!",
    Silence => "Fine. Be that way!",
    Generic => "Whatever."
  }
}

fn sentence_type(message: &str) -> Sentence {
  let trimmed_message = message.trim();

  if trimmed_message.is_empty() { return Silence; }
  if trimmed_message.ends_with("?") { return Question; }
  if trimmed_message.chars().all(|char| !char.is_lowercase()) { return Yelling; }

  Generic
}