¡ ¢ 1 / 31 Freyd is Kleisli, for Arrows Bart Jacobs Ichiro Hasuo Radboud University Nijmegen the Netherlands July 2, 2006 Introduction Introduction Introduction Introducing Arrows Kleisli categories for Arrows 2-categorical characterization of Kleisli categories (Eilenberg-Moore) algebras for Arrows 2 / 31 Interfaces for structured computations (as opposed to pure functions): monads [Moggi’91]