nom::tag!

macro_rules! tag (
  ($i:expr, $inp: expr) => (
    {
      #[inline(always)]
      fn as_bytes<T: $crate::AsBytes>(b: &T) -> &[u8] {
        b.as_bytes()
      }

      let expected = $inp;
      let bytes = as_bytes(&expected);

      if bytes.len() > $i.len() {
        $crate::IResult::Incomplete($crate::Needed::Size(bytes.len()))
      } else if &$i[0..bytes.len()] == bytes {
        $crate::IResult::Done(&$i[bytes.len()..], &$i[0..bytes.len()])
      } else {
        $crate::IResult::Error($crate::Err::Position($crate::ErrorCode::Tag as u32, $i))
      }
    }
  );
);

tag!(&[T]: nom::AsBytes) => &[T] -> IResult<&[T], &[T]> declares a byte array as a suite to recognize

consumes the recognized characters

 named!(x, tag!("abcd"));
 let r = x(&b"abcdefgh"[..]);
 assert_eq!(r, Done(&b"efgh"[..], &b"abcd"[..]));