# Function nom::combinator::map_opt

source · [−]

    pub fn map_opt<I: Clone, O1, O2, E: ParseError<I>, F, G>(
        parser: F,
        f: G
    ) -> impl FnMut(I) -> IResult<I, O2, E> where
        F: Parser<I, O1, E>,
        G: FnMut(O1) -> Option<O2>,

Expand description

Applies a function returning an `Option` over the result of a parser.

    use nom::character::complete::digit1;
    use nom::combinator::map_opt;

    let mut parse = map_opt(digit1, |s: &str| s.parse::<u8>().ok());

    // the parser will convert the result of digit1 to a number
    assert_eq!(parse("123"), Ok(("", 123)));

    // this will fail if digit1 fails
    assert_eq!(parse("abc"), Err(Err::Error(("abc", ErrorKind::Digit))));

    // this will fail if the mapped function fails (a `u8` is too small to hold `123456`)
    assert_eq!(parse("123456"), Err(Err::Error(("123456", ErrorKind::MapOpt))));