Andreas Abel wrote:

I tell them that monads are for sequencing effects; and the sequencing is visible clearly in

(>>) :: IO a -> IO b -> IO b (>>=) :: IO a -> (a -> IO b) -> IO b

but not in

fmap :: (a -> b) -> IO a -> IO b join :: IO (IO a) -> IO a

Indeed! I'd like to point out an old academic paper that was written exactly on the subject at hand: how Category Theory monads relate to monads in Haskell. Here is the relevant quotation: Monads are typically equated with single-threadedness, and are therefore used as a technique for incorporating imperative features into a purely functional language. Category theory monads have little to do with single-threadedness; it is the sequencing imposed by composition that ensures single-threadedness. In a Wadler-ised monad this is a consequence of bundling the Kleisli star and flipped compose into the bind operator. There is nothing new in this connection. Peter Landin in his Algol 60 used functional composition to model semi-colon. Semi-colon can be thought of as a state transforming operator that threads the state of the machine throughout a program. The work of Peyton-Jones and Wadler has turned full circle back to Landin's earlier work as their use of Moggi's sequencing monad enables real side-effects to be incorporated into monad operations such as print. Quoted from: Sec 3: An historical aside Jonathan M. D. Hill and Keith Clarke: An Introduction to Category Theory, Category Theory Monads, and Their Relationship to Functional Programming. 1994. http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.53.6497 I'd like to stress: the single-threadedness, the trick that lets us embed imperative language into a pure one, has *little to do* with category-theoretic monads with their Klesli star. The web page http://okmij.org/ftp/Computation/IO-monad-history.html describes the work of Landin in detail, contrasting Landin's and Peyton-Jones' papers.