为自定义数字类型启用 -Woverflowed-literals

Question

默认情况下，如果文字的精度对其类型而言太大，GHC 会启用 -Woverflowed-literals

 警告

发出消息：

OverflowedLiterals.hs:10:12: warning: [GHC-97441] [-Woverflowed-literals]
    Literal 258 is out of the Word8 range 0..255
   |
10 |     print (258 :: Word8)
   |            ^^^

OverflowedLiterals.hs:15:12: warning: [GHC-97441] [-Woverflowed-literals]
    Literal 9223372036854775817 is out of the Int range -9223372036854775808..9223372036854775807
   |
15 |     print (9223372036854775817 :: Int)
   |            ^^^^^^^^^^^^^^^^^^^

有没有办法为自定义数字类型启用此警告？

例如，我想要这个代码

data Word4 = Word4 Bool Bool Bool Bool
instance Num Word4 where
  ...

main = print (17 :: Word4)

导致编译器抱怨

StackoverflowExample:LINE:COL: warning: [GHC-97441] [-Woverflowed-literals]
    Literal 17 is out of the Word4 range 0..15

Answer 1

没有，或者至少在撰写本文时没有ghc

。检查此问题的代码位于

here [GitHub]：

warnAboutOverflowedLiterals dflags lit
 | wopt Opt_WarnOverflowedLiterals dflags
 , Just (i, tc) <- lit
 = if
    -- These only show up via the 'HsOverLit' route
    | sameUnique tc intTyConName        -> check i tc minInt         maxInt
    | sameUnique tc wordTyConName       -> check i tc minWord        maxWord
    | sameUnique tc int8TyConName       -> check i tc (min' @Int8)   (max' @Int8)
    | sameUnique tc int16TyConName      -> check i tc (min' @Int16)  (max' @Int16)
    | sameUnique tc int32TyConName      -> check i tc (min' @Int32)  (max' @Int32)
    | sameUnique tc int64TyConName      -> check i tc (min' @Int64)  (max' @Int64)
    | sameUnique tc word8TyConName      -> check i tc (min' @Word8)  (max' @Word8)
    | sameUnique tc word16TyConName     -> check i tc (min' @Word16) (max' @Word16)
    | sameUnique tc word32TyConName     -> check i tc (min' @Word32) (max' @Word32)
    | sameUnique tc word64TyConName     -> check i tc (min' @Word64) (max' @Word64)
    | sameUnique tc naturalTyConName    -> checkPositive i tc

    -- These only show up via the 'HsLit' route
    | sameUnique tc intPrimTyConName    -> check i tc minInt         maxInt
    | sameUnique tc wordPrimTyConName   -> check i tc minWord        maxWord
    | sameUnique tc int8PrimTyConName   -> check i tc (min' @Int8)   (max' @Int8)
    | sameUnique tc int16PrimTyConName  -> check i tc (min' @Int16)  (max' @Int16)
    | sameUnique tc int32PrimTyConName  -> check i tc (min' @Int32)  (max' @Int32)
    | sameUnique tc int64PrimTyConName  -> check i tc (min' @Int64)  (max' @Int64)
    | sameUnique tc word8PrimTyConName  -> check i tc (min' @Word8)  (max' @Word8)
    | sameUnique tc word16PrimTyConName -> check i tc (min' @Word16) (max' @Word16)
    | sameUnique tc word32PrimTyConName -> check i tc (min' @Word32) (max' @Word32)
    | sameUnique tc word64PrimTyConName -> check i tc (min' @Word64) (max' @Word64)

因此，它对不同的（隐式）数据构造函数进行硬编码，以与

Int

、

Word

、

Int16

、

Word32

 等一起使用，从而检查相应的下限和上限。

严格来说，也许有可能，但目前尚未实现。如果我们知道

17

 转换为的类型是 

Num

 和 

Bounded

 的实例，那么检查它可能会有点复杂，因为它只是将 

17

 转换为

fromInteger 17

。