動態轉化類型

Question

我試圖反序列化數據流，包含（概念上）對("TypeName", "blah"，其中"blah"對read適用於某些類型爲TypeName的對象。

有沒有辦法動態選擇read的結果類型？我會使用類似Data.Dynamic還是Data.Typable？

Answer 1

這應該指向你在正確的方向：

import Data.Typeable 
import Data.Dynamic 
import Control.Applicative 

readMay :: Read a => String -> Maybe a 
readMay s = case reads s of 
    (a,[]):_ -> Just a 
    _ -> Nothing 

reconstruct :: Typeable a => (Maybe a -> r) -> (String, String) -> r 
reconstruct k (typ,val) = 
    case typ of 
     "string" -> k $ cast =<< (readMay val :: Maybe String) 
     "int" -> k $ cast =<< (readMay val :: Maybe Int) 
     "double" -> k $ cast =<< (readMay val :: Maybe Double) 

reconstructToDyn (typ,val) = 
    case typ of 
     "string" -> toDyn <$> (readMay val :: Maybe String) 
     "int" -> toDyn <$> (readMay val :: Maybe Int) 
     "double" -> toDyn <$> (readMay val :: Maybe Double)