generalizes permutations

generalperms.hs

select [] = []
select (x : xs) = (x, xs) : map (fmap (x :)) (select xs)


perm2 ks = [[x,y] | (x, ys) <- select ks, y <- ys]

permute 2 xs = perm2 xs
permute n xs = join [[x : p | p <- (permute (n-1) ys)] | (x,ys) <- select xs]