Rust: Using 'collect' after we map something which might fail

collect_example.rs

impl FromStr for LanguageTag {
    fn from_str(s: &str) -> Option<LanguageTag> {
        fn parse(s: &str) -> Option<Tag> { from_str(s) }
        let parsed: Option<Vec<Tag>> = collect(s.split('-').map(parse));
        match parsed {
            Some(components) => Some(LanguageTag { components: components }),
            None => None
        }
    }
}