Chapter 7: Higher-order functions

@carlosgaldino and @laurocaetano Finally I finished the chapter 7 exercises.

The exercise 7 took me some time because it wasn't work as I expected. But, once I did the evaluation steps it  was easy to fix it.

The exercises 8 and 9, not sure if it was the best solution.
but I have to agree that adding the parity bit in the beginning makes easier to write the parity functions.