Sorting in haskell with parameter using higher order function

Question

Hi I\'m a Haskell beginner and I\'m really lost. This is for my assignment, and it asks me to do something like below using higer order function

Main> mySort          


        

Answer 1

You're not supposed to match against those functions specifically. It defeats the purpose of using a higher-order function in the first place. In fact, you can't write it like this, since there is no general way of comparing functions.

Instead, use the passed function directly for the sorting. That way, it will work for any suitable comparison function, not just the ones you've explicitly written code for.

For example, imagine the task was to combine two values using a passed operator:

combine (+) 2 3 = 5
combine (*) 3 5 = 15
combine max 10 100 = 100

You would solve it like this:

combine op x y = x `op` y

Can you use a similar approach to solving the sorting problem?

Hint: You may want to define a helper function to transform the passed comparison function into a form suitable for sortBy:

compareUsing :: (a -> a -> Bool) -> (a -> a -> Ordering)
compareUsing op x y = ...