rotor::rotor_compose!

macro_rules! rotor_compose {
    (pub enum $name:ident/$cname:ident <$context_type:ident>
        { $($x:ident ($y:ty),)* }) => { ... };
    (enum $name:ident/$cname:ident <$context_type:ident>
        { $($x:ident ($y:ty),)* }) => { ... };
    (@machine $name:ident/$cname:ident $ctx_typ:ident
        [ $(<$ctx_name:ident $(: $ctx_bound:ident)*>)* ]
        $($iname:ident ($itype:ty),)*) => { ... };
}