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 consumes input before failing.

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());