Macro peel_ip::prelude::length_data

macro_rules! length_data {
    ( $ i : expr , $ submac : ident ! ( $ ( $ args : tt ) * ) ) => { ... };
    ( $ i : expr , $ f : expr ) => { ... };
}

length_data!(I -> IResult<I, nb>) => O

length_data gets a number from the first parser, than takes a subslice of the input of that size, and returns that subslice