Haskell, How many elements from one list are present in the other list : I am new to functional programming using Haskell and I can't seem to be able to create a function that takes two lists as arguments and returns how many elements there are common in both lists.
e.g. f [1, 2, 4, 2] [2, 3, 4, 4] returning 2 (repetitions are ignored).
Any suggestions?