partition1 _ [] = ([], [])
partition1 f (x:xs) = 
  let (ys, zs) = partition1 f xs
  in if f x
    then (x:ys, zs)
    else (ys, x:zs)

partition2 _ [] = ([], [])
partition2 f (x:xs) 
  | f x       = (x:ys, zs)
  | otherwise = (ys, x:zs)
  where (ys, zs) = partition2 f xs
  
main = do
  print $ partition1 odd [1..6]
  print $ partition2 odd [1..6]