Macro impl_chain_transducer 

macro_rules! impl_chain_transducer {
    (@impl $T_head:ident, $($T_tail:ident)*, $($T_init:ident)*, $T_last:ident, $($T:ident)*, $($a:ident)*, $($b:ident)*, $($c:ident)*) => { ... };
    (@inc $T0:ident $($T:ident)*, $($a:ident)*, $($b:ident)*, $($c:ident)*, $TT:ident $aa:ident $bb:ident $cc:ident) => { ... };
    (@inc , $($a:ident)*, $($b:ident)*, $($c:ident)*, $TT:ident $aa:ident $bb:ident $cc:ident $($tt:tt)*) => { ... };
    (@inc $T0:ident $($T:ident)*, $($a:ident)*, $($b:ident)*, $($c:ident)*, $TT:ident $aa:ident $bb:ident $cc:ident $($tt:tt)*) => { ... };
    ($($tt:tt)*) => { ... };
}