This is my solution to the challenge. You have to use the interactive console down in the bottom because you have to check the type of the result, not the actual value. It doesn't use any loops, because how would loops make sense with types?

To run: click run and type something like :t mult two two into the console. It will return something like mult two two :: Succ (Succ (Succ (Succ Zero))), which means 4.

The amount of Succs is the answer.