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.

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:

...

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’