Haskell: 对柯里化数据使用模式匹配

Question

是否可以使用与柯里化数据匹配的模式？假设如下代码：

data Bind = Echo String | Sum Int Int

getOperation (Echo  x )  =  "Echo"
getOperation (Sum  x y ) = "Sum"

main = getOperation (Sum 1)

失败，因为 Sum 1 的类型为 Int -> Bind，而 getOperation 的类型为 Bind -> String。

我的意图是获得一个字符串来标识所使用的数据构造函数，即使数据是柯里化的。类似于这个假代码：

getOperation (Echo  x )  =  "Echo"
getOperation (Echo) = "Echo"       -- Pattern matching for curried data
getOperation (Sum  x y ) = "Sum"
getOperation (Sum x) = "Sum"       -- Pattern matching for curried data

Answer 1

为值附加名称没有问题。

data Named a = Named { name :: String, value :: a }

-- there is a very natural Functor instance for Named as well, which
-- could be used to implement this
(<$$>) :: Named (a -> b) -> a -> Named b
Named n f <$$> x = Named n (f x)

下面是如何使用它的示例：

data Bind = Echo String | Add Int Int

echo :: Named (String -> Bind)
add  :: Named (Int -> Int -> Bind)
add  = Named "Add" Add
echo = Named "Echo" Echo

main = do
    putStrLn . name $ echo
    putStrLn . name $ echo <$$> "hi"
    putStrLn . name $ add
    putStrLn . name $ add <$$> 3
    putStrLn . name $ add <$$> 3 <$$> 4

这会产生：

Echo
Echo
Add
Add
Add

Haskell: 对柯里化数据使用模式匹配

Haskell: Using patten matching with currying data

haskell

currying