I don't want to solve your problem for you - I believe the solution should be your own work. However, I will provide a list of functions which could assist you, and which you don't have to import:
filter f list: returns all elements of list where f element returns True. For instance, filter (\x -> (x /= 0)) [0,1,0,2,3] gives [1,2,3]. This is useful with the not function, which inverts a Bool; for instance, filter (\x -> not (x > 2)) [1,2,3,4,5] gives [1,2].all f list: returns True if f gives True for all elements of list. For example, all (\x -> (x /= 0)) [1,2,3] gives True; however, all (\x -> (x /= 0)) [1,0,2,3] gives False.x `elem` list (which is really just syntax sugar for elem x list) returns true if x is an element of list. For example, 1 `elem` [1,2,3] gives True, but 0 `elem` [1,2,3] gives False.
Again, I won't directly give you the solution to this problem. But I can guarantee you that if you put the above functions together in the right way - together with the Just and Nothing constructors - you can make your complement function.
