/// Solutions to some exercises by Alisa Feistel.
/// Included here for their relevance to the whole Monad theme.
/// Also, Alisa is too lazy to put them in a separate project for now.
#[cfg(test)]
mod tests {
    fn bind<T, F: FnOnce(T) -> Option<T>>(f: F, fa: Option<T>) -> Option<T> {
        match fa {
            Some(a) => f(a),
            None => None,
        }
    }

    #[test]
    fn test() {
        assert_eq!(bind(|x: i32| Some(x + 3), Some(2)), Some(5));
        assert_eq!(bind(|x: i32| Some(x + 3), None), None);
        assert_eq!(bind(|_: i32| None, Some(2)), None);
        assert_eq!(bind(|_: i32| None, None), None);

        assert_eq!(bind(|x: &str| Some(x), Some("apple")), Some("apple"));
        assert_eq!(
            bind(|_: &str| Some("banana"), Some("apple")),
            Some("banana")
        );

        let banana = "banana".to_string();
        assert_eq!(
            bind(|_: &str| Some(banana.as_str()), Some("apple")),
            Some("banana")
        );

        let banana = "banana".to_string();
        assert_eq!(
            bind(|_: String| Some(banana), Some("apple".to_string())),
            Some("banana".to_string())
        );
    }
}

#[cfg(test)]
mod reftests {
    fn refbind<'a, 'b, T: 'a + ?Sized, F: 'a + Fn(&'a T) -> Option<&'b T>>(
        f: F,
        fa: Option<&'a T>,
    ) -> Option<&'b T> {
        match fa {
            Some(a) => f(a),
            None => None,
        }
    }

    #[test]
    fn test() {
        let apple = "apple".to_string();
        let banana = "banana".to_string();
        assert_eq!(
            refbind(|_: &String| Some(&banana), Some(&apple)),
            Some(&banana)
        );

        let banana = "banana";
        assert_eq!(refbind(|_: &str| Some(banana), Some("apple")), Some(banana));
    }
}