gistfile1.ml

// F#
let transformPrefs
  (prefs:Map<string, Map<string, float>>) =
  
  let add k1 k2 v m =
    let curInner = 
        match Map.tryfind k1 m with
        | None   -> Map.empty
        | Some x -> x
    m |> Map.add k1 (Map.add k2 v curInner)
  
  Map.fold_right (fun key1 value1 state1 -> 
    Map.fold_right (fun key2 value2 state2 ->
      add key2 key1 value2 state2
    ) value1 state1
  ) prefs Map.empty

-- Haskell
transformPrefs :: Map String (Map String Double)
transformPrefs m =
  Map.fromListWith Map.union . concatMap (\(x, y) -> [(a, Map.singleton x b) | (a, b) <- Map.toList y]) . Map.toList $ Map.fromList m