The "kind of" being really pertinent. In particular, this forgoes the guarantee that the only thing the transducer is allowed to do is return a value from the r

The "kind of" being really pertinent. In particular, this forgoes the guarantee that the only thing the transducer is allowed to do is return a value from the reduction. Hickey notes that this is a law of writing a proper transducer. Higher rank types ensure that this law is properly encoded directly into the system. That said, I'm pretty sure you know this :)