Recursion Haskell

Define a recursive function of type isEven :: Integer -> Bool that returns true if the input integer is even, and false otherwise (dont use the mod operator!) If you are stuck, work the steps of solving a problem recursively by divide-and-conquer. Initially ignore negative numbers but consider them once you have it solved for positive numbers.

Addendum: of course, in isEven, we could have used the mod operator instead and written:

isEven n = mod n 2 == 0