{- Setup -}
type Nat = Maybe Int

{- Task 1 -}
nat :: Int -> Nat
nat _ = undefined

{- Task 2 -}
consEither :: a -> Either e [a] -> Either e [a]
consEither _ _ = undefined

{- Task 3 -}
limit :: Nat -> [a] -> Either Nat [a]
limit _ _ = undefined

{- Task 4 -}
skip :: Nat -> [a] -> Either Nat [a]
skip _ _ = undefined

{- Task 5 -}
split :: Int -> [a] -> Either Int [[a]]
split _ _ = undefined

{- Tests -}
tests = do
  -- nat
  check "nat1" "Just 10" (nat 10)
  check "nat2" "Nothing" (nat (-1))
  -- consEither
  check "consEither1" "Right [1,2,3,4,5]" (consEither 1 (Right [2..5]) :: Either Int [Int])
  check "consEither2" "Left True" (consEither 1 (Left True) :: Either Bool [Int])
  -- limit
  check "limit1" "Right [1,2]" (limit (nat 2) [1,2,3])
  check "limit2" "Right \"hell\"" (limit (nat 4) "hello")
  check "limit3" "True" (isLeft (limit (nat 10) "hello"))
  -- skip
  check "skip1" "Right [3]" (skip (nat 2) [1,2,3])
  check "skip2" "Right \"o\"" (skip (nat 4) "hello")
  check "skip3" "True" (isLeft (skip (nat 10) [True]))
  -- split
  check "split1" "Right [[]]" (split 0 ([] :: [Int]))
  check "split2" "Left 1" (split 1 ([] :: [Int]))
  check "split3" "Left 0" (split 0 [1..4])
  check "split4" "Right [[1],[2],[3],[4]]" (split 1 [1..4])
  check "split5" "Right [[1,2],[3,4]]" (split 2 [1..4])
  check "split6" "Left 3" (split 3 [1..4])
  check "split7" "Right [[1,2,3,4]]" (split 4 [1..4])
  where isLeft (Left _) = True
        isLeft _ = False

check name e c = do
  putStr ("*** " ++ name ++ ": ")
  if show c == e then putStrLn "OK"
  else putStrLn ("ERROR; expected '" ++ e ++ "', but found '" ++ show c ++ "'")