[moomin]

Haskell beginner here:

Re: the characterisation, the only thing I'd add is that they have explicit start and end calls. Start resets the state, end can clean up resources if necessary.

I tried thinking about what output structure a generalised transducer would form, and came to the conclusion it was a foldable monoid i.e. pretty list-like.

[tel]

From what I've seen Transducers tend to use Clojure's ambient state mechanics to get local state to each "transduction step". If you want to do away with that then you can embed the state in a Fold (which is basically a Moore FSA) and then think of transducers as Fold transformers which aren't allowed to touch their output.