nom::take_s

macro_rules! take_s {
    ($i:expr, $count:expr) => { ... };
}

take_s!(nb) => &str -> IResult<&str, &str> generates a parser consuming the specified number of characters

 // Desmond parser
 named!(take5<&str,&str>, take_s!( 5 ) );

 let a = "abcdefgh";

 assert_eq!(take5(a), Done("fgh", "abcde"));