content: filterAndFold :: (a -> Bool) -> (a -> a -> a) -> [a] -> a
  filterAndFold _ _ [] = error "Empty list"
  filterAndFold f op (x:xs) = foldl op x (filter f xs)
  
  main :: IO ()
  main = print (filterAndFold odd (+) [1, 2, 3, 4, 5, 6])
  