On Sun, Aug 17, 2008 at 11:27 AM, Yitzchak Gale <[EMAIL PROTECTED]> wrote:
> There, Twan van Laarhoven designs the implementation > of the permutations function that is slated to be included in > GHC 6.10. I look forward to Twan's design. I found the Haskell 1.3 definition. > -- permutations xs returns the list of all permutations of xs. > -- e.g., permutations "abc" == ["abc","bac","bca","acb","cab","cba"] > permutations :: [a] -> [[a]] > permutations [] = [[]] > permutations (x:xs) = [zs | ys <- permutations xs, zs <- interleave x ys > ] > where interleave :: a -> [a] -> [[a]] > interleave x [] = [[x]] > interleave x (y:ys) = [x:y:ys] ++ map (y:) (interleave x ys) I like the use of list comprehension, but I was surprised the last line was not: > interleave x (y:ys) = (x:y:ys) : map (y:) (interleave x ys) John _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
