Consider the following suggestions for the standard Haskell library `List'. ------------------------------------------------------------------------ import List (intersprerse, insertBy) compose :: [a -> a] -> a -> a -- just appropriate name compose = foldr (.) id insertBy2 :: (a -> b) -> Comparison b -> a -> [a] -> [a] insertBy2 f cp a xs = map fst $ insertBy (\ p p' -> cp (snd p) (snd p')) (a, f a) [(x, f x) | x <- xs] Similar are mergeBy2, sortBy2. type ComparisonValue = LT | GT | Eq deriving ... -- better name than `Ordering' type Comparison a = a -> a -> ComparisonValue ------------------------------------------------------------------------ Motivation example for `compose': myShowsList :: Show a => [a] -> String -> String myShowsList xs = compose $ intersperse (", "++) $ map shows xs myShowsList ("; "++) [1,2,3] --> "1; 2; 3" Motivation example for insertBy2: Consider the program insertBy (\ n m -> compare (f n) (f m)) 100 [0 .. 1000], where f :: Integer -> Integer is expensive to compute. We see that the program insertBy2 f compare 100 [1 .. 1000] spends 2 times less of `f' invocations, and looks natural. ----------------- Serge Mechveliani mechvel@botik.ru