默認情況下，使用Scientific時輸入'Double'的限制

Question

我有兩個科學數字，它們是我想要轉換爲Ints的整數，如下所示。

請忽略代碼慣例和代碼的慣用性。

> import qualified Data.Vector as V 
> import Data.Scientific 

> cToTy (Array v) = case V.toList v of 
>  [String nm, Number p, Number s] 
>  | all (==True) $ map isInteger [p,s] -- We make sure they're always integers 
>  , [pr,sc] <- map (forceEitherToInt . floatingOrInteger) [p,s] -- And then hack them out 

> forceEitherToInt :: (RealFloat r, Integral i) => Either r i -> Int 
> forceEitherToInt (Left _a) = 0 -- This shouldn't happen, so we'll default it to 0 all the time. 
> forceEitherToInt (Right a) = fromIntegral a 

但是，我得到這個警告，我不知道如何擺脫他們。

JsonUtils.lhs:76:26: Warning: 
    Defaulting the following constraint(s) to type ‘Double’ 
     (RealFloat r0) arising from a use of ‘forceEitherToInt’ 
    In the first argument of ‘(.)’, namely ‘forceEitherToInt’ 
    In the first argument of ‘map’, namely 
     ‘(forceEitherToInt . floatingOrInteger)’ 
    In a stmt of a pattern guard for 
        a case alternative: 
     [pr, sc] <- map (forceEitherToInt . floatingOrInteger) [p, s] 

有沒有人有任何想法或想法？

Answer 1

首先，如果「不應該發生」，您可以明確地導致錯誤;第二，你可以放棄RealFloat作爲@bheklilr狀態;第三你可以更具體地指定雙倍，如果你更喜歡雙倍;第四，如果你在名字中寫'A從B'而不是'B到A'，它可以幫助匈牙利語。所以，你可以，例如寫：

intFromEither :: (Integral i) => Either Double i -> Int 
intFromEither (Left d) = error $ 
    "intFromEither tried to coerce `Left " ++ show d ++ "` to an Int." 
intFromEither (Right i) = fromIntegral i 

，可隨時更換Double以上x，使之更加普遍;這裏最常用的簽名是(Integral a, Num b) => Either t a -> b。