  We revisit once again the connection between three notions of computation:
monads, arrows and idioms (also called applicative functors). We employ
monoidal categories of finitary functors and profunctors on finite sets as
models of these notions of computation, and develop the connections between
them through adjunctions. As a result, we obtain a categorical version of
Lindley, Yallop and Wadler's characterisation of monads and idioms as arrows
satisfying an isomorphism.
