A good first step would be understanding how the other entry works: cartProd :: [a] -> [b] -> [(a,b)] cartProd xs ys = do x <- xs y <- ys return (x,y)
It is about halfway between the two choices. John On Thu, Feb 9, 2012 at 9:37 AM, readams <richard.ad...@lvvwd.com> wrote: > 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-tp3085649p5470185.html > Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe