take.hs

take' :: Int -> [a] -> [a]
take' n _
  | n <= 0              =  []
take' _ []              =  []
take' n (x:xs)          =  x : take' (n - 1) xs        -- 先に整数値で場合分け, トップレベルで pattern match

take'2 n xxs
  | n <= 0     =  []
  | otherwise  =  case xxs of
                    []    ->  []
                    x:xs  ->  x : take'2 (n - 1) xs  -- 先に整数値で場合分け, case で pattern match

take'3 _ []     =  []
take'3 n (x:xs)
  | n <= 0     =  []
  | otherwise  =  x : take'3 (n - 1) xs              -- 先にリストで場合分け, トップレベルで pattern match

take'4 :: Int -> [a] -> [a]
take'4 n xxs = case xxs of
  []              -> []
  _:_  | n <= 0   -> []
  x:xs            -> x : take'4 (n - 1) xs           -- 先にリストで場合分け, caseで pattern match