Macro nom::verify

macro_rules! verify {
    ($i : expr, $submac : ident! ($($args : tt) *), $g : expr) => { ... };
    ($i : expr, $submac : ident! ($($args : tt) *), $submac2 : ident!
 ($($args2 : tt) *)) => { ... };
    ($i : expr, $f : expr, $g : expr) => { ... };
    ($i : expr, $f : expr, $submac : ident! ($($args : tt) *)) => { ... };
}

verify!(I -> IResult<I, O>, O -> bool) => I -> IResult<I, O> returns the result of the child parser if it satisfies a verification function

 named!(check<u32>, verify!(nom::number::streaming::be_u32, |val: &u32| *val < 3));