No-frills permutation code in Haskell

Permutation.hs

module Permutation where
  permutate :: [a] -> [[a]]
  permutate [x1,x2] = [[x1,x2],[x2,x1]]
  permutate items = concat $ map p $ getEachInFrontOnce items
      where
        p (x:xs) = map (\items -> [x]++items) $ permutate xs
        getEachInFrontOnce items = map (putItemAtIndexToFront items) [0..length items-1]
        putItemAtIndexToFront items idx = [items!!idx] ++ take idx items ++ drop (idx+1) items