Function chomp::combinators::or

pub fn or<I: Input, T, E, F, G>(i: I, f: F, g: G) -> ParseResult<I, T, E> where
    F: FnOnce(I) -> ParseResult<I, T, E>,
    G: FnOnce(I) -> ParseResult<I, T, E>, 

Tries to match the parser f, if f fails it tries g. Returns the success value of the first match, otherwise the error of the last one if both fail.

Incomplete state is propagated from the first one to report incomplete.

If multiple or combinators are used in the same expression, consider using the parse! macro and its alternation operator (<|>).

use chomp::prelude::{Error, parse_only, or, token};

let p = |i| or(i,
            |i| token(i, b'a'),
            |i| token(i, b'b'));

assert_eq!(parse_only(&p, b"abc"), Ok(b'a'));
assert_eq!(parse_only(&p, b"bbc"), Ok(b'b'));
assert_eq!(parse_only(&p, b"cbc"), Err((&b"cbc"[..], Error::expected(b'b'))));