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));