This should do: combinations :: [[a]] -> [[a]] combinations [] = [[]] combinations [[x]] = [[x]] combinations ([] : xxs) = combinations xxs combinations ((h : tl) : xxs) = [h : r | r <- combinations xxs] ++ if null tl then [] else combinations (tl : xxs) Bernd developer@imaginando.net schrieb:

Hi,

I need a functions which takes as argument a list of lists like this one:

[[1,2],[3],[4]]

and gives me a list of list with all the possible combinations like this one:

[[1,3,4],[2,3,4]]

In this case there are only 2 combinations but if there was more than one element in the other lists the results were much more.

I'm a little stuck in this simple problem.

First i was thinking in cartesian product but then i realized that i may not be what i really need.

Any tip?

Many thx,

Nuno Santos

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Sounds like cartesian product to me. So you could try combinations [] = [[]] combinations (xs:xss) = liftM2 (:) xs (combinations xss) -- Lennart developer@imaginando.net wrote:

Hi,

I need a functions which takes as argument a list of lists like this one:

[[1,2],[3],[4]]

and gives me a list of list with all the possible combinations like this one:

[[1,3,4],[2,3,4]]

In this case there are only 2 combinations but if there was more than one element in the other lists the results were much more.

I'm a little stuck in this simple problem.

First i was thinking in cartesian product but then i realized that i may not be what i really need.

Any tip?

Many thx,

Nuno Santos

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

developer@imaginando.net wrote:

I need a functions which takes as argument a list of lists like this one:

[[1,2],[3],[4]]

and gives me a list of list with all the possible combinations like this one:

[[1,3,4],[2,3,4]]

sequence Finding out why it is named that strangely is left as an excercise. :-) Udo. -- The future isn't what it used to be. (It never was.)