He ends up calling that `mapping` later mapping :: (a -> b) -> Transducer b a mapping f xf r a = xf r (f a) which, modulo a little renaming, eta-expan

He ends up calling that `mapping` later mapping :: (a -> b) -> Transducer b a mapping f xf r a = xf r (f a) which, modulo a little renaming, eta-expansion, and point elimination is the same as your `trans`