List stats

-- Task: take a list and return a tuple with a number of items
-- satisfying a predicate and a list of the items.

-- a verbose solution
stats :: (a -> Bool) -> [a] -> (Int, [a])
stats f xs = (count 0 f xs, filter f xs)
  where
    count a _ [] = a
    count a f (x:xs)
      | f x = count (a + 1) f xs
      | otherwise = count a f xs

-- a terse solution
stats :: (a -> Bool) -> [a] -> (Int, [a])
stats f xs = (length sl, sl)
  where
    sl = filter f xs

-- stats (> 5) [0..9] → (4,[6,7,8,9])