I am posting the same question again because I had not subscribed to the list and I received a message saying it was automatically rejected. I have the following function that takes an element and a list and inserts the element into the list at the first position where it is less than or equal to the next element. So, if the list is sorted, then the list will remain sorted. myInsert :: Ord a => a -> [a] -> [a] myInsert x [] = [x] myInsert x (y:ys) = if x < y then x:y:ys else y:myInsert x ys Now, I have to use the above function myInsert and foldr to implement another function called insertionSort. I have been able to do it without using foldr as follows and it works just fine: insertionSort :: Ord a => [a] -> [a] insertionSort [] = [] insertionSort [x] = [x] insertionSort (x:xs) = myInsert x (insertionSort xs) I have worked for 2 days to use foldr without success, for example: insertionSort :: Ord a => [a] -> [a] insertionSort [] = [] insertionSort [x] = [x] insertionSort (x:xs) = foldr (myInsert) x (insertionSort xs) But it does not even compile, I get the following error which refers to last instruction at position "x" in "foldr (myInsert) x (insertionSort xs)": Couldn't match expected type ‘[a]’ with actual type ‘a’ I will very much appreciate your feedback in order to solve my issue. Best regards.