另一個Haskell類型的困境

Question

大家好，我正在嘗試編寫此代碼，但數據類型存在問題

data Collection = Set [Int] deriving (Show)

remove :: Int -> Collection -> Collection
remove _ (Set []) = (Set [])
remove numberToRemove (Set (x:xs))
    |x == numberToRemove = (Set xs)
    |otherwise = Set ([x]:remove numberToRemove xs)

我收到此錯誤，它是類型的問題：

 Couldn't match expected type `Int' with actual type `[t0]'
In the first argument of `(:)', namely `[x]'
In the first argument of `Set', namely
  `([x] : remove numberToRemove xs)'
In the expression: Set ([x] : remove numberToRemove xs)
Failed, modules loaded: none.

任何幫助表示贊賞，謝謝

Answer 1

第一個問題，在表達式中：

Set ([x] : remove numberToRemove xs)

列表的開頭（在：之前）必須是Int，而不是[Int]，並替換為：

Set (x : remove numberToRemove xs)

然后，第二個問題。 在相同的表達式中，子表達式：

remove numberToRemove xs

是Collecion，但運算符后必須有[Int]：因此，可能的解決方案：

data Collection = Set [Int] deriving (Show)

col_to_list :: Collection -> [Int]
col_to_list (Set xs) = xs

remove :: Int -> Collection -> Collection
remove _ (Set []) = (Set [])
remove numberToRemove (Set (x:xs))
    |x == numberToRemove = (Set xs)
    |otherwise = Set (x : col_to_list (remove numberToRemove (Set xs)))