Macro combine::choice

macro_rules! choice {
    ($first : expr) => { ... };
    ($first : expr, $($rest : expr),+) => { ... };
}

Takes a number of parsers and tries to apply them each in order. Fails if all the parsers fails or if an applied parser fails after it has committed to its parse.

let mut parser = choice!(
    many1(digit()),
    string("let").map(|s| s.to_string()),
    many1(letter()));
assert_eq!(parser.parse("let"), Ok(("let".to_string(), "")));
assert_eq!(parser.parse("123abc"), Ok(("123".to_string(), "abc")));
assert!(parser.parse(":123").is_err());