Haskell - permutations

perms.hs

import Control.Monad

enumerate xs = zip [1..] xs 

dlists :: [a] -> [(a, [a])]
dlists xs = [(x, [y | (j, y) <- enumerate xs, j /= i]) | (i, x) <- enumerate xs]

permute (x:y:[]) = [y:x:[], x:y:[]]
permute xs = let difflist = dlists xs
                in join [map (i:) (permute d) | (i, d) <- difflist]