swap02.hs

swap i j xs = let a = slice' 0     (i-1)
                  b = slice' (i+1) (j-1)
                  c = slice' (j+1) (length xs - 1) 
              in a ++ (xs!!j):b ++ (xs!!i):c
    where
      slice' i j = slice i j xs
                   
slice i j = snd . splitAt i . fst . splitAt (j+1)