Haskell：使用patten匹配与柯里化数据

Question

是否可以使用patten匹配与柯里化数据？假设下面的代码：

data Bind = Echo String | Sum Int Int 

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

main = getOperation (Sum 1) 

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

我的意思是获取一个字符串，即使数据已被curried，也可以使用数据构造函数。像这样的假代码：

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

将名称附加到值是没有问题的。

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一个样本：

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 

这将产生：

Echo 
Echo 
Add 
Add 
Add