Author here. Slightly simplifying, a Kleisli arrow is just a function from `A` to `M<B>`, and which is composable, similar to function composition:

    Kleisli<M, A, B> + Kleisli<M, B, C> = Kleisli<M, A, C>

Although it is an important part of how the conduits work, it is not strictly necessary for using the library.

Would it help if I clarified that somewhere, or would you rather not read "Kleisli" anywhere in the docs?