Macro nom::named_args

macro_rules! named_args {
    ($vis : vis $func_name : ident($($arg : ident : $typ : ty), *) < $return_type
 : ty >, $submac : ident! ($($args : tt) *)) => { ... };
    ($vis : vis $func_name : ident < 'a > ($($arg : ident : $typ : ty), *) <
 $return_type : ty >, $submac : ident! ($($args : tt) *)) => { ... };
    ($vis : vis $func_name : ident($($arg : ident : $typ : ty), *) < $input_type :
 ty, $return_type : ty >, $submac : ident! ($($args : tt) *)) => { ... };
    ($vis : vis $func_name : ident < 'a > ($($arg : ident : $typ : ty), *) <
 $input_type : ty, $return_type : ty >, $submac : ident! ($($args : tt) *)) => { ... };
}

Makes a function from a parser combination with arguments.

//takes [`&[u8]`] as input
named_args!(tagged(open_tag: &[u8], close_tag: &[u8])<&str>,
  delimited!(tag!(open_tag), map_res!(take!(4), str::from_utf8), tag!(close_tag))
);
//takes `&str` as input
named_args!(tagged(open_tag: &str, close_tag: &str)<&str, &str>,
  delimited!(tag!(open_tag), take!(4), tag!(close_tag))
);

Note: if using arguments that way gets hard to read, it is always possible to write the equivalent parser definition manually, like this:

fn tagged(input: &[u8], open_tag: &[u8], close_tag: &[u8]) -> IResult<&[u8], &str> {
  // the first combinator in the tree gets the input as argument. It is then
  // passed from one combinator to the next through macro rewriting
  delimited!(input,
    tag!(open_tag), take!(4), tag!(close_tag)
  )
);