Hello, I am fairly conversant in category. In any case, I am re-reading Bart Jacobs co-algebra tutorial citeseer.ist.psu.edu/jacobs97tutorial.html and draft book www.cs.ru.nl/B.Jacobs/CLG/JacobsCoalgebraIntro.pdf. Have others read these? What role do co-algebras play in Haskell stateful computations (as opposed to or complementing monads)? Kind regards, Vasili