另一个haskell类型的困境

Question

嘿大家我想写这个代码,我遇到了数据类型的问题

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)

我收到此错误,它的类型有问题:

 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.

任何帮助表示赞赏谢谢

Answer 1

第一个问题,在表达式中:

Set ([x] : remove numberToRemove xs)

列表的头部(在:之前)必须是Int,而不是[Int],替换为:

Set (x : remove numberToRemove xs)

然后,第二个问题.在同一个表达式中,子表达式:

remove numberToRemove xs

是一个Collecion,但是在运算符之后必须有一个[Int]:所以,一个可能的解决方案:

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)))