inssortBy :: (a -> b) -> [Int] -> [Int]
inssortBy _ [] = []
inssortBy f (a:xs) = insertBy f a (inssortBy xs)

insertBy :: (a -> b) -> Int -> [Int] -> [Int]
insertBy _ a [] = [a]
insertBy f a (x:xs)
  | f a < f x = a:x:xs
  | otherwise = x : insertBy f a xs