Macro silk_router::predicates

macro_rules! predicates {
    ($iter:ident, $body:expr, $first:tt, $( $rest:tt )+) => { ... };
    ($iter:ident, $body:expr, $first:tt) => { ... };
    ($iter:ident, $body:expr, $first:ident = $parser:expr, $( $rest:tt )+) => { ... };
    ($iter:ident, $body:expr, $first:ident = $parser:expr) => { ... };
}