Count Uppercase and Lowercase Letters
Write a recursive function count-upper-lower that takes a non-empty string as its argument and returns a tuple containing the counts of how many letters in the string are uppercase and how many are lowercase (in that order).
To solve this problem you will need to write a function that returns a pair of values (i.e., a tuple).
For example, suppose we wanted to write a function that returned the sum and product of two values passed as arguments to the function. We might write this code.