Function chomp::combinators::either

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

Attempts the left parser first and then the right parser if the first parser fails. Result is returned as an Either<T, U> depending on which parser succeeded.

NOTE: If both parsers have the same return-type, use or instead.

use chomp::prelude::{Error, parse_only, either, token, Left, Right};

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

assert_eq!(parse_only(&p, b"a"), Ok(Left(b'a')));
assert_eq!(parse_only(&p, b"b"), Ok(Right(b'b')));
assert_eq!(parse_only(&p, b"c"), Err((&b"c"[..], Error::expected(b'b'))));