I'm not sure offhand. Even if your language lacks it, however, you can usually get away without it. The following works

    Transducer r a b = (r -> b -> r) -> (r -> a -> r)

but if you even accidentally specialize the `r` while constructing Transducers then you will have reduced their ability to generalize over input and output containers. In other words, it'll be up to you to maintain the universality of `r`.