Nice explanation. However, at http://stackoverflow.com/questions/4119730/cartesian-product it was pointed out that this cartProd :: [a] -> [b] -> [(a, b)] cartProd = liftM2 (,) is equivalent to the cartesian product produced using a list comprehension: cartProd xs ys = [(x,y) | x <- xs, y <- ys] I do not see how your method of explanation can be used to explain this equivalence? Nevertheless, can you help me to understand how liftM2 (,) achieves the cartesian product? For example, Prelude Control.Monad.Reader> liftM2 (,) [1,2] [3,4,5] [(1,3),(1,4),(1,5),(2,3),(2,4),(2,5)] Thank you! -- View this message in context: http://haskell.1045720.n5.nabble.com/Cannot-understand-liftM2-tp3085649p5470... Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.