Macro peel_ip::prelude::cond_reduce

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

cond_reduce!(bool, I -> IResult<I,O>) => I -> IResult<I, O> Conditional combinator with error

Wraps another parser and calls it if the condition is met. This combinator returns an error if the condition is false

This is especially useful if a parser depends on the value returned by a preceding parser in a do_parse!.

 let b = true;
 let f = closure!(&'static[u8],
   cond_reduce!( b, tag!("abcd") )
 );

 let a = b"abcdef";
 assert_eq!(f(&a[..]), Done(&b"ef"[..], &b"abcd"[..]));

 let b2 = false;
 let f2 = closure!(&'static[u8],
   cond_reduce!( b2, tag!("abcd") )
 );
 assert_eq!(f2(&a[..]), Error(error_position!(ErrorKind::CondReduce, &a[..])));