Macro compare 

macro_rules! compare {
    ($(#[$meta:meta])*,
     $compare:ident,
     $left_slice:ty,
     $right_slice:ty,
     $split_prefix:ident,
     $left_to_iter:ident,
     $right_to_iter:ident,
     $self:ident,
     $left_tail:ident,
     $right_tail:ident,
     $primary_check:block,
     $variable_top:ident,
    ) => { ... };
}