count :: A -> [A] -> Int
-- testing 13 combinations of argument values
-- looking through 2 candidates of size 1
-- looking through 0 candidates of size 2
-- looking through 1 candidates of size 3
-- looking through 0 candidates of size 4
-- looking through 3 candidates of size 5
-- looking through 2 candidates of size 6
-- looking through 13 candidates of size 7
-- looking through 16 candidates of size 8
-- looking through 57 candidates of size 9
-- looking through 84 candidates of size 10
-- looking through 242 candidates of size 11
-- looking through 401 candidates of size 12
-- looking through 1045 candidates of size 13
-- looking through 1895 candidates of size 14
-- looking through 4672 candidates of size 15
-- looking through 8990 candidates of size 16
count x xs = if null xs then 0 else count x (tail xs) + (if x == head xs then 1 else 0)