nom::is_a_s

macro_rules! is_a_s {
    ($input:expr, $arr:expr) => { ... };
}

is_a_s!(&str) => &str -> IResult<&str, &str> returns the longest list of characters that appear in the provided array

 named!(abcd<&str, &str>, is_a_s!( "abcd" ));

 let r1 = abcd("aaaaefgh");
 assert_eq!(r1, Done("efgh", "aaaa"));

 let r2 = abcd("dcbaefgh");
 assert_eq!(r2, Done("efgh", "dcba"));