Hi, Give a try to this library: http://hackage.haskell.org/package/permutation You can construct the combinations with list of indices and then apply it to your sets.
[]s Victor On Fri, Mar 12, 2010 at 5:16 AM, Ketil Malde <ke...@malde.org> wrote: > Casey Hawthorne <cas...@istar.ca> writes: > >>> For example, I have this: >>>list1 = [a, b, c] >>>list2 = [d, e, f] >>>list3 = [g, h, i] > >> Think in abstract terms what you want to accomplish. > > A bit more specifically, let's say the input is a list of lists, and you > want to produce all combinations of drawing one element from each of the > input lists¹: > > perms :: [[a]] -> [[a]] > > You need to consider two cases, when the input is empty, and when the > input contains at least one list of elements: > > perms (l:ls) = ... > perms [] = ... > > The second case shouldn't be so hard. > > Now, if you pretend that 'perms' is already implemented, then you can > use it to generate all permutations for the tail of the input list. The > first case boils down to combining the first input list with all > permutations of the rest of the lists: > > perms (l:ls) = ... l ... perms ls > > Does this help? > > -k > > ¹ Using tuples is harder to generalize for length, but nicer typewise, > since you'd get something like 'perms :: ([a],[b],..[x]) -> [(a,b,..,x)] > -- > If I haven't seen further, it is by standing in the footprints of giants > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- GNU/Linux user #446397 - http://counter.li.org _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
