Write a function that takes a string and calculates the number of letters and digits within it. Return the result as anonymous type in string format.
count_all("Hello World") ➞ "{ LETTERS = 10, DIGITS = 0 }"
count_all("H3ll0 Wor1d") ➞ "{ LETTERS = 7, DIGITS = 3 }"
count_all("149990") ➞ "{ LETTERS = 0, DIGITS = 6 }"