haskell - Haskell：为自定义类型派生 Show

Question

我有这个类型定义：

data Operace = Op (Int->Int->Int) String (Int->Int->Int) deriving Show

我想将此类型打印到交互式外壳（GHCi）中。应该打印的只是String字段。

我试过这个：

instance Show Operace where
    show (Op op str inv) = show str

但我仍然不断得到

No instance for (Show (Int -> Int -> Int))
  arising from the 'deriving' clause of a data type declaration
Possible fix:
  add an instance declaration for (Show (Int -> Int -> Int))
  or use a standalone 'deriving instance' declaration,
       so you can specify the instance context yourself
When deriving the instance for (Show Operace)

我不想添加Showfor (Int->Int->Int)，我只想打印字符串。

感谢帮助！

编辑：

为了将来参考，固定版本是：

data Operace = Op (Int->Int->Int) String (Int->Int->Int)

instance Show Operace where
    show (Op _ str _) = str

Answer 1

您所做的实例声明是正确的方法。您似乎忘记deriving从原始data声明中删除该错误条款。

data Operace = Op (Int->Int->Int) String (Int->Int->Int)

instance Show Operace where
   show (Op op str inv) = show str

Answer 2

您可以派生Show，只需先导入Text.Show.Functions。