[Haskell-cafe] Deleting list of elements from Data.Set

My strictness analyser in my brain hurts. Which one (foldl,foldl',foldr) is the best way? Prelude Data.Set Data.List> let s = fromList [1,2,3,4,5] Loading package array-0.1.0.0 ... linking ... done. Loading package containers-0.1.0.0 ... linking ... done. Prelude Data.Set Data.List> foldl (.) id (Data.List.map Data.Set.delete [1,3,5]) s fromList [2,4] Prelude Data.Set Data.List> foldl' (.) id (Data.List.map Data.Set.delete [1,3,5]) s fromList [2,4] Prelude Data.Set Data.List> foldr (.) id (Data.List.map Data.Set.delete [1,3,5]) s fromList [2,4] Which one is best? -- Gracjan