-- Exponential complexity
-- NOTE: This should never be used it is extraordinarily slow
fib :: Int -> Integer
fib 0 = 0
fib 1 = 1
fib n = fib (n - 1) + fib (n - 2)

-- > fib 8
-- > [0, 1, 1, 2, 3, 5, 8, 13]